draft-ietf-avt-rtp-rfc3984bis-12.txt   rfc6184.txt 
Obsoletes RFC 3984
Audio/Video Transport WG Y.-K. Wang
Internet Draft Huawei Technologies
Intended status: Standards track R. Even
Expires: April 2011 Self-employed
T. Kristensen
Tandberg
R. Jesup
WorldGate Communications
October 9, 2010
RTP Payload Format for H.264 Video Internet Engineering Task Force (IETF) Y.-K. Wang
draft-ietf-avt-rtp-rfc3984bis-12.txt Request for Comments: 6184 R. Even
Obsoletes: 3984 Huawei Technologies
Category: Standards Track T. Kristensen
ISSN: 2070-1721 Tandberg
R. Jesup
WorldGate Communications
May 2011
Status of this Memo RTP Payload Format for H.264 Video
This Internet-Draft is submitted to IETF in full conformance with Abstract
the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This memo describes an RTP Payload format for the ITU-T
Task Force (IETF), its areas, and its working groups. Note that Recommendation H.264 video codec and the technically identical
other groups may also distribute working documents as Internet- ISO/IEC International Standard 14496-10 video codec, excluding the
Drafts. Scalable Video Coding (SVC) extension and the Multiview Video Coding
extension, for which the RTP payload formats are defined elsewhere.
The RTP payload format allows for packetization of one or more
Network Abstraction Layer Units (NALUs), produced by an H.264 video
encoder, in each RTP payload. The payload format has wide
applicability, as it supports applications from simple low bitrate
conversational usage, to Internet video streaming with interleaved
transmission, to high bitrate video-on-demand.
Internet-Drafts are draft documents valid for a maximum of six This memo obsoletes RFC 3984. Changes from RFC 3984 are summarized
months and may be updated, replaced, or obsoleted by other in Section 14. Issues on backward compatibility to RFC 3984 are
documents at any time. It is inappropriate to use Internet-Drafts discussed in Section 15.
as reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at Status of This Memo
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at This is an Internet Standards Track document.
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 9, 2009. This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Copyright and License Notice Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6184.
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Abstract
This memo describes an RTP Payload format for the ITU-T
Recommendation H.264 video codec and the technically identical
ISO/IEC International Standard 14496-10 video codec, excluding the
Scalable Video Coding (SVC) extension and the Multivew Video Coding
extension, for which the RTP payload formats are defined elsewhere.
The RTP payload format allows for packetization of one or more
Network Abstraction Layer Units (NALUs), produced by an H.264 video
encoder, in each RTP payload. The payload format has wide
applicability, as it supports applications from simple low bit-rate
conversational usage, to Internet video streaming with interleaved
transmission, to high bit-rate video-on-demand.
This memo obsoletes RFC 3984. Changes from RFC 3984 are summarized
in section 15. Issues on backward compatibility to RFC 3984 are
discussed in section 14.
Table of Contents Table of Contents
Table of Contents................................................2 1. Introduction ....................................................4
1. Introduction..................................................4 1.1. The H.264 Codec ............................................4
1.1. The H.264 Codec..........................................4 1.2. Parameter Set Concept ......................................5
1.2. Parameter Set Concept....................................6 1.3. Network Abstraction Layer Unit Types .......................6
1.3. Network Abstraction Layer Unit Types.....................6 2. Conventions .....................................................7
2. Conventions...................................................7 3. Scope ...........................................................7
3. Scope.........................................................8 4. Definitions and Abbreviations ...................................7
4. Definitions and Abbreviations.................................8 4.1. Definitions ................................................7
4.1. Definitions..............................................8 4.2. Abbreviations ..............................................9
4.2. Abbreviations...........................................10 5. RTP Payload Format .............................................10
5. RTP Payload Format...........................................11 5.1. RTP Header Usage ..........................................10
5.1. RTP Header Usage........................................11 5.2. Payload Structures ........................................12
5.2. Payload Structures......................................13 5.3. NAL Unit Header Usage .....................................13
5.3. NAL Unit Header Usage...................................14 5.4. Packetization Modes .......................................16
5.4. Packetization Modes.....................................16 5.5. Decoding Order Number (DON) ...............................17
5.5. Decoding Order Number (DON).............................18 5.6. Single NAL Unit Packet ....................................19
5.6. Single NAL Unit Packet..................................20 5.7. Aggregation Packets .......................................20
5.7. Aggregation Packets.....................................21 5.7.1. Single-Time Aggregation Packet (STAP) ..............22
Table 4. Type field for STAPs and MTAPs........................22 5.7.2. Multi-Time Aggregation Packets (MTAPs) .............25
5.7.1. Single-Time Aggregation Packet.....................23 5.8. Fragmentation Units (FUs) .................................29
5.7.2. Multi-Time Aggregation Packets (MTAPs).............26 6. Packetization Rules ............................................33
5.7.3. Fragmentation Units (FUs)..........................29 6.1. Common Packetization Rules ................................33
6. Packetization Rules..........................................33 6.2. Single NAL Unit Mode ......................................34
6.1. Common Packetization Rules..............................33 6.3. Non-Interleaved Mode ......................................34
6.2. Single NAL Unit Mode....................................34 6.4. Interleaved Mode ..........................................34
6.3. Non-Interleaved Mode....................................34 7. De-Packetization Process .......................................35
6.4. Interleaved Mode........................................35 7.1. Single NAL Unit and Non-Interleaved Mode ..................35
7. De-Packetization Process.....................................35 7.2. Interleaved Mode ..........................................35
7.1. Single NAL Unit and Non-Interleaved Mode................35 7.2.1. Size of the De-Interleaving Buffer .................36
7.2. Interleaved Mode........................................36 7.2.2. De-Interleaving Process ............................36
7.2.1. Size of the De-interleaving Buffer.................36 7.3. Additional De-Packetization Guidelines ....................38
7.2.2. De-interleaving Process............................37
7.3. Additional De-Packetization Guidelines..................38
8. Payload Format Parameters....................................39
8.1. Media Type Registration.................................39
8.2. SDP Parameters..........................................58
8.2.1. Mapping of Payload Type Parameters to SDP..........58
8.2.2. Usage with the SDP Offer/Answer Model..............59
8.2.3. Usage in Declarative Session Descriptions..........69
8.3. Examples................................................70
Offer SDP:......................................................76
Answer SDP:.....................................................76
8.4. Parameter Set Considerations............................77
8.5. Decoder Refresh Point Procedure using In-Band Transport of
Parameter Sets (Informative).................................80
8.5.1. IDR Procedure to Respond to a Request for a Decoder
Refresh Point.............................................80
8.5.2. Gradual Recovery Procedure to Respond to a Request for
a Decoder Refresh Point...................................81
9. Security Considerations......................................82
10. Congestion Control..........................................82
11. IANA Consideration..........................................83
12. Informative Appendix: Application Examples..................83
12.1. Video Telephony according to ITU-T Recommendation H.241
Annex A......................................................84
12.2. Video Telephony, No Slice Data Partitioning, No NAL Unit
Aggregation..................................................84
12.3. Video Telephony, Interleaved Packetization Using NAL Unit
Aggregation..................................................84
12.4. Video Telephony with Data Partitioning.................85
12.5. Video Telephony or Streaming with FUs and Forward Error
Correction...................................................86
12.6. Low Bit-Rate Streaming.................................88
12.7. Robust Packet Scheduling in Video Streaming............89
13. Informative Appendix: Rationale for Decoding Order Number...90
13.1. Introduction...........................................90
13.2. Example of Multi-Picture Slice Interleaving............90
13.3. Example of Robust Packet Scheduling....................92
13.4. Robust Transmission Scheduling of Redundant Coded Slices96
13.5. Remarks on Other Design Possibilities..................96
14. Backward Compatibility to RFC 3984..........................97
15. Changes from RFC 3984.......................................99
16. Acknowledgements...........................................101
17. References.................................................101
17.1. Normative References..................................101
17.2. Informative References................................102
18. Authors' Addresses.........................................104
1. Introduction 8. Payload Format Parameters ......................................39
8.1. Media Type Registration ...................................39
8.2. SDP Parameters ............................................57
8.2.1. Mapping of Payload Type Parameters to SDP ..........57
8.2.2. Usage with the SDP Offer/Answer Model ..............58
8.2.3. Usage in Declarative Session Descriptions ..........66
8.3. Examples ..................................................68
8.4. Parameter Set Considerations ..............................75
8.5. Decoder Refresh Point Procedure Using In-Band
Transport of Parameter Sets (Informative)..................78
8.5.1. IDR Procedure to Respond to a Request for
a Decoder Refresh Point ............................78
8.5.2. Gradual Recovery Procedure to Respond to
a Request for a Decoder Refresh Point ..............79
9. Security Considerations ........................................79
10. Congestion Control ............................................80
11. IANA Considerations ...........................................81
12. Informative Appendix: Application Examples ....................81
12.1. Video Telephony According to Annex A of ITU-T
Recommendation H.241 .....................................81
12.2. Video Telephony, No Slice Data Partitioning, No
NAL Unit Aggregation .....................................82
12.3. Video Telephony, Interleaved Packetization Using
NAL Unit Aggregation .....................................82
12.4. Video Telephony with Data Partitioning ...................83
12.5. Video Telephony or Streaming with FUs and Forward
Error Correction .........................................83
12.6. Low Bitrate Streaming ....................................86
12.7. Robust Packet Scheduling in Video Streaming ..............86
13. Informative Appendix: Rationale for Decoding Order Number .....87
13.1. Introduction .............................................87
13.2. Example of Multi-Picture Slice Interleaving ..............88
13.3. Example of Robust Packet Scheduling ......................89
13.4. Robust Transmission Scheduling of Redundant Coded
Slices ...................................................93
13.5. Remarks on Other Design Possibilities ....................94
14. Changes from RFC 3984 .........................................94
15. Backward Compatibility to RFC 3984 ............................96
16. Acknowledgements ..............................................98
17. References ....................................................98
17.1. Normative References .....................................98
17.2. Informative References ...................................99
This memo specifies an RTP payload specification for the video 1. Introduction
coding standard known as ITU-T Recommendation H.264 [1] and ISO/IEC
International Standard 14496 Part 10 [2] (both also known as This memo specifies an RTP payload specification for the video coding
Advanced Video Coding, or AVC). In this memo the name H.264 is standard known as ITU-T Recommendation H.264 [1] and ISO/IEC
used for the codec and the standard, but the memo is equally International Standard 14496-10 [2] (both also known as Advanced
applicable to the ISO/IEC counterpart of the coding standard. Video Coding (AVC)). In this memo, the name H.264 is used for the
codec and the standard, but this memo is equally applicable to the
ISO/IEC counterpart of the coding standard.
This memo obsoletes RFC 3984. Changes from RFC 3984 are summarized This memo obsoletes RFC 3984. Changes from RFC 3984 are summarized
in section 15. Issues on backward compatibility to RFC 3984 are in Section 14. Issues on backward compatibility to RFC 3984 are
discussed in section 14. discussed in Section 15.
1.1. The H.264 Codec 1.1. The H.264 Codec
The H.264 video codec has a very broad application range that The H.264 video codec has a very broad application range that covers
covers all forms of digital compressed video, from low bit-rate all forms of digital compressed video, from low bitrate Internet
Internet streaming applications to HDTV broadcast and Digital streaming applications to HDTV broadcast and Digital Cinema
Cinema applications with nearly lossless coding. Compared to the applications with nearly lossless coding. Compared to the current
current state of technology, the overall performance of H.264 is state of technology, the overall performance of H.264 is such that
such that bit rate savings of 50% or more are reported. Digital bitrate savings of 50% or more are reported. Digital Satellite TV
Satellite TV quality, for example, was reported to be achievable at quality, for example, was reported to be achievable at 1.5 Mbit/s,
1.5 Mbit/s, compared to the current operation point of MPEG 2 video compared to the current operation point of MPEG 2 video at around 3.5
at around 3.5 Mbit/s [10]. Mbit/s [10].
The codec specification [1] itself distinguishes conceptually The codec specification [1] itself conceptually distinguishes between
between a video coding layer (VCL) and a network abstraction layer a Video Coding Layer (VCL) and a Network Abstraction Layer (NAL).
(NAL). The VCL contains the signal processing functionality of the The VCL contains the signal processing functionality of the codec;
codec; mechanisms such as transform, quantization, and motion mechanisms such as transform, quantization, and motion-compensated
compensated prediction; and a loop filter. It follows the general prediction; and a loop filter. It follows the general concept of
concept of most of today's video codecs, a macroblock-based coder most of today's video codecs, a macroblock-based coder that uses
that uses inter picture prediction with motion compensation and inter picture prediction with motion compensation and transform
transform coding of the residual signal. The VCL encoder outputs coding of the residual signal. The VCL encoder outputs slices: a bit
slices: a bit string that contains the macroblock data of an string that contains the macroblock data of an integer number of
integer number of macroblocks, and the information of the slice macroblocks and the information of the slice header (containing the
header (containing the spatial address of the first macroblock in spatial address of the first macroblock in the slice, the initial
the slice, the initial quantization parameter, and similar quantization parameter, and similar information). Macroblocks in
information). Macroblocks in slices are arranged in scan order slices are arranged in scan order unless a different macroblock
unless a different macroblock allocation is specified, by using the allocation is specified using the syntax of slice groups. In-picture
so-called Flexible Macroblock Ordering syntax. In-picture prediction is used only within a slice. More information is provided
prediction is used only within a slice. More information is in [10].
provided in [10].
The Network Abstraction Layer (NAL) encoder encapsulates the slice The NAL encoder encapsulates the slice output of the VCL encoder into
output of the VCL encoder into Network Abstraction Layer Units (NAL Network Abstraction Layer Units (NALUs), which are suitable for
units), which are suitable for transmission over packet networks or transmission over packet networks or for use in packet-oriented
use in packet oriented multiplex environments. Annex B of H.264 multiplex environments. Annex B of H.264 defines an encapsulation
defines an encapsulation process to transmit such NAL units over process to transmit such NALUs over bytestream-oriented networks. In
byte-stream oriented networks. In the scope of this memo, Annex B the scope of this memo, Annex B is not relevant.
is not relevant.
Internally, the NAL uses NAL units. A NAL unit consists of a one- Internally, the NAL uses NAL units. A NAL unit consists of a one-
byte header and the payload byte string. The header indicates the byte header and the payload byte string. The header indicates the
type of the NAL unit, the (potential) presence of bit errors or type of the NAL unit, the (potential) presence of bit errors or
syntax violations in the NAL unit payload, and information syntax violations in the NAL unit payload, and information regarding
regarding the relative importance of the NAL unit for the decoding the relative importance of the NAL unit for the decoding process.
process. This RTP payload specification is designed to be unaware This RTP payload specification is designed to be unaware of the bit
of the bit string in the NAL unit payload. string in the NAL unit payload.
One of the main properties of H.264 is the complete decoupling of One of the main properties of H.264 is the complete decoupling of the
the transmission time, the decoding time, and the sampling or transmission time, the decoding time, and the sampling or
presentation time of slices and pictures. The decoding process presentation time of slices and pictures. The decoding process
specified in H.264 is unaware of time, and the H.264 syntax does specified in H.264 is unaware of time, and the H.264 syntax does not
not carry information such as the number of skipped frames (as is carry information such as the number of skipped frames (as is common
common in the form of the Temporal Reference in earlier video in the form of the Temporal Reference in earlier video compression
compression standards). Also, there are NAL units that affect many standards). Also, there are NAL units that affect many pictures and
pictures and that are, therefore, inherently timeless. For this that are, therefore, inherently timeless. For this reason, the
reason, the handling of the RTP timestamp requires some special handling of the RTP timestamp requires some special considerations
considerations for NAL units for which the sampling or presentation for NAL units for which the sampling or presentation time is not
time is not defined or, at transmission time, unknown. defined or, at transmission time, is unknown.
1.2. Parameter Set Concept 1.2. Parameter Set Concept
One very fundamental design concept of H.264 is to generate self- One very fundamental design concept of H.264 is to generate self-
contained packets, to make mechanisms such as the header contained packets, to make mechanisms such as the header duplication
duplication of RFC 4629 [11] or MPEG-4 Visual's Header Extension of RFC 4629 [11] or MPEG-4 Visual's Header Extension Code (HEC) [12]
Code (HEC) [12] unnecessary. This was achieved by decoupling unnecessary. This was achieved by decoupling information relevant to
information relevant to more than one slice from the media stream. more than one slice from the media stream. This higher-layer meta
This higher layer meta information should be sent reliably, information should be sent reliably, asynchronously, and in advance
asynchronously, and in advance from the RTP packet stream that from the RTP packet stream that contains the slice packets.
contains the slice packets. (Provisions for sending this (Provisions for sending this information in-band are also available
information in-band are also available for applications that do not for applications that do not have an out-of-band transport channel
have an out-of-band transport channel appropriate for the purpose.) appropriate for the purpose). The combination of the higher-level
The combination of the higher-level parameters is called a parameters is called a parameter set. The H.264 specification
parameter set. The H.264 specification includes two types of includes two types of parameter sets: sequence parameter sets and
parameter sets: sequence parameter set and picture parameter set. picture parameter sets. An active sequence parameter set remains
An active sequence parameter set remains unchanged throughout a unchanged throughout a coded video sequence, and an active picture
coded video sequence, and an active picture parameter set remains parameter set remains unchanged within a coded picture. The sequence
unchanged within a coded picture. The sequence and picture and picture parameter set structures contain information such as
parameter set structures contain information such as picture size, picture size, optional coding modes employed, and macroblock to slice
optional coding modes employed, and macroblock to slice group map. group map.
To be able to change picture parameters (such as the picture size) To be able to change picture parameters (such as the picture size)
without having to transmit parameter set updates synchronously to without having to transmit parameter set updates synchronously to the
the slice packet stream, the encoder and decoder can maintain a slice packet stream, the encoder and decoder can maintain a list of
list of more than one sequence and picture parameter set. Each more than one sequence and picture parameter set. Each slice header
slice header contains a codeword that indicates the sequence and contains a codeword that indicates the sequence and picture parameter
picture parameter set to be used. set to be used.
This mechanism allows the decoupling of the transmission of This mechanism allows the decoupling of the transmission of parameter
parameter sets from the packet stream, and the transmission of them sets from the packet stream and the transmission of them by external
by external means (e.g., as a side effect of the capability means (e.g., as a side effect of the capability exchange) or through
exchange), or through a (reliable or unreliable) control protocol. a (reliable or unreliable) control protocol. It may even be possible
It may even be possible that they are never transmitted but are that they are never transmitted but are fixed by an application
fixed by an application design specification. design specification.
1.3. Network Abstraction Layer Unit Types 1.3. Network Abstraction Layer Unit Types
Tutorial information on the NAL design can be found in [13], [14], Tutorial information on the NAL design can be found in [13], [14],
and [15]. and [15].
All NAL units consist of a single NAL unit type octet, which also All NAL units consist of a single NAL unit type octet, which also
co-serves as the payload header of this RTP payload format. The co-serves as the payload header of this RTP payload format. A
payload of a NAL unit follows immediately. description of the payload of a NAL unit follows.
The syntax and semantics of the NAL unit type octet are specified The syntax and semantics of the NAL unit type octet are specified in
in [1], but the essential properties of the NAL unit type octet are [1], but the essential properties of the NAL unit type octet are
summarized below. The NAL unit type octet has the following format: summarized below. The NAL unit type octet has the following format:
+---------------+ +---------------+
|0|1|2|3|4|5|6|7| |0|1|2|3|4|5|6|7|
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|F|NRI| Type | |F|NRI| Type |
+---------------+ +---------------+
The semantics of the components of the NAL unit type octet, as The semantics of the components of the NAL unit type octet, as
specified in the H.264 specification, are described briefly below. specified in the H.264 specification, are described briefly below.
F: 1 bit F: 1 bit
forbidden_zero_bit. The H.264 specification declares a value of forbidden_zero_bit. The H.264 specification declares a
1 as a syntax violation. value of 1 as a syntax violation.
NRI: 2 bits NRI: 2 bits
nal_ref_idc. A value of 00 indicates that the content of the nal_ref_idc. A value of 00 indicates that the content of
NAL unit is not used to reconstruct reference pictures for inter the NAL unit is not used to reconstruct reference pictures
picture prediction. Such NAL units can be discarded without for inter picture prediction. Such NAL units can be
risking the integrity of the reference pictures. Values greater discarded without risking the integrity of the reference
than 00 indicate that the decoding of the NAL unit is required pictures. Values greater than 00 indicate that the decoding
to maintain the integrity of the reference pictures. of the NAL unit is required to maintain the integrity of the
reference pictures.
Type: 5 bits Type: 5 bits
nal_unit_type. This component specifies the NAL unit payload nal_unit_type. This component specifies the NAL unit
type as defined in Table 7-1 of [1], and later within this memo. payload type as defined in Table 7-1 of [1] and later within
For a reference of all currently defined NAL unit types and this memo. For a reference of all currently defined NAL
their semantics, please refer to section 7.4.1 in [1]. unit types and their semantics, please refer to Section
7.4.1 in [1].
This memo introduces new NAL unit types, which are presented in This memo introduces new NAL unit types, which are presented in
section 5.2. The NAL unit types defined in this memo are marked as Section 5.2. The NAL unit types defined in this memo are marked as
unspecified in [1]. Moreover, this specification extends the unspecified in [1]. Moreover, this specification extends the
semantics of F and NRI as described in section 5.3. semantics of F and NRI as described in Section 5.3.
2. Conventions 2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
this document are to be interpreted as described in RFC 2119 [4]. document are to be interpreted as described in RFC 2119 [4].
This specification uses the notion of setting and clearing a bit This specification uses the notion of setting and clearing a bit when
when bit fields are handled. Setting a bit is the same as bit fields are handled. Setting a bit is the same as assigning that
assigning that bit the value of 1 (On). Clearing a bit is the same bit the value of 1 (On). Clearing a bit is the same as assigning
as assigning that bit the value of 0 (Off). that bit the value of 0 (Off).
3. Scope 3. Scope
This payload specification can only be used to carry the "naked" This payload specification can only be used to carry the "naked"
H.264 NAL unit stream over RTP, and not the bitstream format H.264 NAL unit stream over RTP and not the bitstream format discussed
discussed in Annex B of H.264. Likely, the first applications of in Annex B of H.264. Likely, the first applications of this
this specification will be in the conversational multimedia field, specification will be in the conversational multimedia field, video
video telephony or video conferencing, but the payload format also telephony or video conferencing, but the payload format also covers
covers other applications, such as Internet streaming and TV over other applications, such as Internet streaming and TV over IP.
IP.
4. Definitions and Abbreviations 4. Definitions and Abbreviations
4.1. Definitions 4.1. Definitions
This document uses the definitions of [1]. The following terms, This document uses the definitions of [1]. The following terms,
defined in [1], are summed up for convenience: defined in [1], are summed up for convenience:
access unit: A set of NAL units always containing a primary access unit: A set of NAL units always containing a primary coded
coded picture. In addition to the primary coded picture, an picture. In addition to the primary coded picture, an access unit
access unit may also contain one or more redundant coded may also contain one or more redundant coded pictures or other NAL
pictures or other NAL units not containing slices or slice data units not containing slices or slice data partitions of a coded
partitions of a coded picture. The decoding of an access unit picture. The decoding of an access unit always results in a
always results in a decoded picture. decoded picture.
coded video sequence: A sequence of access units that consists, coded video sequence: A sequence of access units that consists, in
in decoding order, of an instantaneous decoding refresh (IDR) decoding order, of an instantaneous decoding refresh (IDR) access
access unit followed by zero or more non-IDR access units unit followed by zero or more non-IDR access units including all
including all subsequent access units up to but not including subsequent access units up to but not including any subsequent IDR
any subsequent IDR access unit. access unit.
IDR access unit: An access unit in which the primary coded IDR access unit: An access unit in which the primary coded picture
picture is an IDR picture. is an IDR picture.
IDR picture: A coded picture containing only slices with I or SI IDR picture: A coded picture containing only slices with I or SI
slice types that causes a "reset" in the decoding process. slice types that causes a "reset" in the decoding process. After
After the decoding of an IDR picture, all following coded the decoding of an IDR picture, all following coded pictures in
pictures in decoding order can be decoded without inter decoding order can be decoded without inter prediction from any
prediction from any picture decoded prior to the IDR picture. picture decoded prior to the IDR picture.
primary coded picture: The coded representation of a picture to primary coded picture: The coded representation of a picture to be
be used by the decoding process for a bitstream conforming to used by the decoding process for a bitstream conforming to H.264.
H.264. The primary coded picture contains all macroblocks of The primary coded picture contains all macroblocks of the picture.
the picture.
redundant coded picture: A coded representation of a picture or redundant coded picture: A coded representation of a picture or a
a part of a picture. The content of a redundant coded picture part of a picture. The content of a redundant coded picture shall
shall not be used by the decoding process for a bitstream not be used by the decoding process for a bitstream conforming to
conforming to H.264. The content of a redundant coded picture H.264. The content of a redundant coded picture may be used by
may be used by the decoding process for a bitstream that the decoding process for a bitstream that contains errors or
contains errors or losses. losses.
VCL NAL unit: A collective term used to refer to coded slice and VCL NAL unit: A collective term used to refer to coded slice and
coded data partition NAL units. coded data partition NAL units.
In addition, the following definitions apply: In addition, the following definitions apply:
decoding order number (DON): A field in the payload structure or decoding order number (DON): A field in the payload structure or a
a derived variable indicating NAL unit decoding order. Values derived variable indicating NAL unit decoding order. Values of
of DON are in the range of 0 to 65535, inclusive. After DON are in the range of 0 to 65535, inclusive. After reaching the
reaching the maximum value, the value of DON wraps around to 0. maximum value, the value of DON wraps around to 0.
NAL unit decoding order: A NAL unit order that conforms to the NAL unit decoding order: A NAL unit order that conforms to the
constraints on NAL unit order given in section 7.4.1.2 in [1]. constraints on NAL unit order given in Section 7.4.1.2 in [1].
NALU-time: The value that the RTP timestamp would have if the NALU-time: The value that the RTP timestamp would have if the NAL
NAL unit would be transported in its own RTP packet. unit would be transported in its own RTP packet.
transmission order: The order of packets in ascending RTP transmission order: The order of packets in ascending RTP sequence
sequence number order (in modulo arithmetic). Within an number order (in modulo arithmetic). Within an aggregation
aggregation packet, the NAL unit transmission order is the same packet, the NAL unit transmission order is the same as the order
as the order of appearance of NAL units in the packet. of appearance of NAL units in the packet.
media aware network element (MANE): A network element, such as a media-aware network element (MANE): A network element, such as a
middlebox or application layer gateway that is capable of middlebox or application layer gateway that is capable of parsing
parsing certain aspects of the RTP payload headers or the RTP certain aspects of the RTP payload headers or the RTP payload and
payload and reacting to the contents. reacting to the contents.
Informative note: The concept of a MANE goes beyond normal Informative note: The concept of a MANE goes beyond normal
routers or gateways in that a MANE has to be aware of the routers or gateways in that a MANE has to be aware of the
signaling (e.g., to learn about the payload type mappings of signaling (e.g., to learn about the payload type mappings of
the media streams), and in that it has to be trusted when the media streams) and that it has to be trusted when working
working with SRTP. The advantage of using MANEs is that they with Secure Real-time Transport Protocol (SRTP). The advantage
allow packets to be dropped according to the needs of the of using MANEs is that they allow packets to be dropped
media coding. For example, if a MANE has to drop packets due according to the needs of the media coding. For example, if a
to congestion on a certain link, it can identify and remove MANE has to drop packets due to congestion on a certain link,
those packets whose elimination produces the least adverse it can identify and remove those packets whose elimination
effect on the user experience. produces the least adverse effect on the user experience.
static macroblock: A certain amount of macroblocks in the video static macroblock: A certain amount of macroblocks in the video
stream can be defined as static, as defined in section 8.3.2.8 stream can be defined as static, as defined in Section 8.3.2.8 in
in [3]. Static macroblocks free up additional processing [3]. Static macroblocks free up additional processing cycles for
cycles for the handling of non-static macroblocks. Based on a the handling of non-static macroblocks. Based on a given amount
given amount of video processing resources and a given of video processing resources and a given resolution, a higher
resolution, a higher number of static macroblocks enables a number of static macroblocks enables a correspondingly higher
correspondingly higher frame rate. frame rate.
default sub-profile: The subset of coding tools, which may be default sub-profile: The subset of coding tools, which may be all
all coding tools of one profile or the common subset of coding coding tools of one profile or the common subset of coding tools
tools of more than one profile, indicated by the profile-level- of more than one profile, indicated by the profile-level-id
id parameter. parameter.
default level: The level indicated by the profile-level-id default level: The level indicated by the profile-level-id
parameter, which consists of three octets, profile_idc, profile- parameter, which consists of three octets, profile_idc, profile-
iop, and level_idc. The default level is indicated by level_idc iop, and level_idc. The default level is indicated by level_idc
in most cases, and, in some cases, additionally by profile-iop. in most cases, and, in some cases, additionally by profile-iop.
4.2. Abbreviations 4.2. Abbreviations
DON: Decoding Order Number DON: Decoding Order Number
DONB: Decoding Order Number Base DONB: Decoding Order Number Base
DOND: Decoding Order Number Difference DOND: Decoding Order Number Difference
FEC: Forward Error Correction FEC: Forward Error Correction
FU: Fragmentation Unit FU: Fragmentation Unit
IDR: Instantaneous Decoding Refresh IDR: Instantaneous Decoding Refresh
IEC: International Electrotechnical Commission IEC: International Electrotechnical Commission
ISO: International Organization for Standardization ISO: International Organization for Standardization
ITU-T: International Telecommunication Union, ITU-T: International Telecommunication Union,
Telecommunication Standardization Sector Telecommunication Standardization Sector
MANE: Media Aware Network Element MANE: Media-Aware Network Element
MTAP: Multi-Time Aggregation Packet MTAP: Multi-Time Aggregation Packet
MTAP16: MTAP with 16-bit timestamp offset MTAP16: MTAP with 16-bit timestamp offset
MTAP24: MTAP with 24-bit timestamp offset MTAP24: MTAP with 24-bit timestamp offset
NAL: Network Abstraction Layer NAL: Network Abstraction Layer
NALU: NAL Unit NALU: NAL Unit
SAR: Sample Aspect Ratio SAR: Sample Aspect Ratio
SEI: Supplemental Enhancement Information SEI: Supplemental Enhancement Information
STAP: Single-Time Aggregation Packet STAP: Single-Time Aggregation Packet
STAP-A: STAP type A STAP-A: STAP type A
STAP-B: STAP type B STAP-B: STAP type B
TS: Timestamp TS: Timestamp
VCL: Video Coding Layer VCL: Video Coding Layer
VUI: Video Usability Information VUI: Video Usability Information
5. RTP Payload Format 5. RTP Payload Format
5.1. RTP Header Usage 5.1. RTP Header Usage
The format of the RTP header is specified in RFC 3550 [5] and The format of the RTP header is specified in RFC 3550 [5] and
reprinted in Figure 1 for convenience. This payload format uses reprinted in Figure 1 for convenience. This payload format uses the
the fields of the header in a manner consistent with that fields of the header in a manner consistent with that specification.
specification.
When one NAL unit is encapsulated per RTP packet, the RECOMMENDED When one NAL unit is encapsulated per RTP packet, the RECOMMENDED RTP
RTP payload format is specified in section 5.6. The RTP payload payload format is specified in Section 5.6. The RTP payload (and the
(and the settings for some RTP header bits) for aggregation packets settings for some RTP header bits) for aggregation packets and
and fragmentation units are specified in sections 5.7 and 5.8, fragmentation units are specified in Sections 5.7.2 and 5.8,
respectively. respectively.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC |M| PT | sequence number | |V=2|P|X| CC |M| PT | sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp | | timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier | | synchronization source (SSRC) identifier |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| contributing source (CSRC) identifiers | | contributing source (CSRC) identifiers |
| .... | | .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 RTP header according to RFC 3550 Figure 1. RTP header according to RFC 3550
The RTP header information to be set according to this RTP payload The RTP header information to be set according to this RTP payload
format is set as follows: format is set as follows:
Marker bit (M): 1 bit Marker bit (M): 1 bit
Set for the very last packet of the access unit indicated by the Set for the very last packet of the access unit indicated by the
RTP timestamp, in line with the normal use of the M bit in video RTP timestamp, in line with the normal use of the M bit in video
formats, to allow an efficient playout buffer handling. For formats, to allow an efficient playout buffer handling. For
aggregation packets (STAP and MTAP), the marker bit in the RTP aggregation packets (STAP and MTAP), the marker bit in the RTP
header MUST be set to the value that the marker bit of the last header MUST be set to the value that the marker bit of the last
NAL unit of the aggregation packet would have been if it were NAL unit of the aggregation packet would have been if it were
transported in its own RTP packet. Decoders MAY use this bit as transported in its own RTP packet. Decoders MAY use this bit as
an early indication of the last packet of an access unit, but an early indication of the last packet of an access unit but MUST
MUST NOT rely on this property. NOT rely on this property.
Informative note: Only one M bit is associated with an Informative note: Only one M bit is associated with an
aggregation packet carrying multiple NAL units. Thus, if a aggregation packet carrying multiple NAL units. Thus, if a
gateway has re-packetized an aggregation packet into several gateway has re-packetized an aggregation packet into several
packets, it cannot reliably set the M bit of those packets. packets, it cannot reliably set the M bit of those packets.
Payload type (PT): 7 bits Payload type (PT): 7 bits
The assignment of an RTP payload type for this new packet format The assignment of an RTP payload type for this new packet format
is outside the scope of this document and will not be specified is outside the scope of this document and will not be specified
here. The assignment of a payload type has to be performed here. The assignment of a payload type has to be performed either
either through the profile used or in a dynamic way. through the profile used or in a dynamic way.
Sequence number (SN): 16 bits Sequence number (SN): 16 bits
Set and used in accordance with RFC 3550. For the single NALU Set and used in accordance with RFC 3550. For the single NALU and
and non-interleaved packetization mode, the sequence number is non-interleaved packetization mode, the sequence number is used to
used to determine decoding order for the NALU. determine decoding order for the NALU.
Timestamp: 32 bits Timestamp: 32 bits
The RTP timestamp is set to the sampling timestamp of the The RTP timestamp is set to the sampling timestamp of the content.
content. A 90 kHz clock rate MUST be used. A 90 kHz clock rate MUST be used.
If the NAL unit has no timing properties of its own (e.g., If the NAL unit has no timing properties of its own (e.g.,
parameter set and SEI NAL units), the RTP timestamp is set to parameter set and SEI NAL units), the RTP timestamp is set to the
the RTP timestamp of the primary coded picture of the access RTP timestamp of the primary coded picture of the access unit in
unit in which the NAL unit is included, according to section which the NAL unit is included, according to Section 7.4.1.2 of
7.4.1.2 of [1]. [1].
The setting of the RTP Timestamp for MTAPs is defined in section The setting of the RTP timestamp for MTAPs is defined in Section
5.7.2. 5.7.2.
Receivers SHOULD ignore any picture timing SEI messages included Receivers SHOULD ignore any picture timing SEI messages included
in access units that have only one display timestamp. Instead, in access units that have only one display timestamp. Instead,
receivers SHOULD use the RTP timestamp for synchronizing the receivers SHOULD use the RTP timestamp for synchronizing the
display process. display process.
If one access unit has more than one display timestamp carried If one access unit has more than one display timestamp carried in
in a picture timing SEI message, then the information in the SEI a picture timing SEI message, then the information in the SEI
message SHOULD be treated as relative to the RTP timestamp, with message SHOULD be treated as relative to the RTP timestamp, with
the earliest event occurring at the time given by the RTP the earliest event occurring at the time given by the RTP
timestamp, and subsequent events later, as given by the timestamp and subsequent events later, as given by the difference
difference in SEI message picture timing values. Let tSEI1, in picture time values carried in the picture timing SEI message.
tSEI2, ..., tSEIn be the display timestamps carried in the SEI
message of an access unit, where tSEI1 is the earliest of all Let tSEI1, tSEI2, ..., tSEIn be the display timestamps carried in
such timestamps. Let tmadjst() be a function that adjusts the the SEI message of an access unit, where tSEI1 is the earliest of
SEI messages time scale to a 90-kHz time scale. Let TS be the all such timestamps. Let tmadjst() be a function that adjusts the
RTP timestamp. Then, the display time for the event associated SEI messages time scale to a 90-kHz time scale. Let TS be the RTP
with tSEI1 is TS. The display time for the event with tSEIx, timestamp. Then, the display time for the event associated with
where x is [2..n] is TS + tmadjst (tSEIx - tSEI1). tSEI1 is TS. The display time for the event with tSEIx, where x
is [2..n], is TS + tmadjst (tSEIx - tSEI1).
Informative note: Displaying coded frames as fields is needed Informative note: Displaying coded frames as fields is needed
commonly in an operation known as 3:2 pulldown, in which film commonly in an operation known as 3:2 pulldown, in which film
content that consists of coded frames is displayed on a content that consists of coded frames is displayed on a display
display using interlaced scanning. The picture timing SEI using interlaced scanning. The picture timing SEI message
message enables carriage of multiple timestamps for the same enables carriage of multiple timestamps for the same coded
coded picture, and therefore the 3:2 pulldown process is picture, and therefore the 3:2 pulldown process is perfectly
perfectly controlled. The picture timing SEI message controlled. The picture timing SEI message mechanism is
mechanism is necessary because only one timestamp per coded necessary because only one timestamp per coded frame can be
frame can be conveyed in the RTP timestamp. conveyed in the RTP timestamp.
5.2. Payload Structures 5.2. Payload Structures
The payload format defines three different basic payload structures. The payload format defines three different basic payload structures.
A receiver can identify the payload structure by the first byte of A receiver can identify the payload structure by the first byte of
the RTP packet payload, which co-serves as the RTP payload header the RTP packet payload, which co-serves as the RTP payload header
and, in some cases, as the first byte of the payload. This byte is and, in some cases, as the first byte of the payload. This byte is
always structured as a NAL unit header. The NAL unit type field always structured as a NAL unit header. The NAL unit type field
indicates which structure is present. The possible structures are indicates which structure is present. The possible structures are as
as follows: follows.
Single NAL Unit Packet: Contains only a single NAL unit in the Single NAL Unit Packet: Contains only a single NAL unit in the
payload. The NAL header type field will be equal to the original payload. The NAL header type field is equal to the original NAL unit
NAL unit type; i.e., in the range of 1 to 23, inclusive. Specified type, i.e., in the range of 1 to 23, inclusive. Specified in Section
in section 5.6. 5.6.
Aggregation Packet: Packet type used to aggregate multiple NAL Aggregation Packet: Packet type used to aggregate multiple NAL units
units into a single RTP payload. This packet exists in four into a single RTP payload. This packet exists in four versions, the
versions, the Single-Time Aggregation Packet type A (STAP-A), the Single-Time Aggregation Packet type A (STAP-A), the Single-Time
Single-Time Aggregation Packet type B (STAP-B), Multi-Time Aggregation Packet type B (STAP-B), Multi-Time Aggregation Packet
Aggregation Packet (MTAP) with 16-bit offset (MTAP16), and Multi- (MTAP) with 16-bit offset (MTAP16), and Multi-Time Aggregation Packet
Time Aggregation Packet (MTAP) with 24-bit offset (MTAP24). The (MTAP) with 24-bit offset (MTAP24). The NAL unit type numbers
NAL unit type numbers assigned for STAP-A, STAP-B, MTAP16, and assigned for STAP-A, STAP-B, MTAP16, and MTAP24 are 24, 25, 26, and
MTAP24 are 24, 25, 26, and 27, respectively. Specified in section 27, respectively. Specified in Section 5.7.
5.7.
Fragmentation Unit: Used to fragment a single NAL unit over Fragmentation Unit: Used to fragment a single NAL unit over multiple
multiple RTP packets. Exists with two versions, FU-A and FU-B, RTP packets. Exists with two versions, FU-A and FU-B, identified
identified with the NAL unit type numbers 28 and 29, respectively. with the NAL unit type numbers 28 and 29, respectively. Specified in
Specified in section 5.8. Section 5.8.
Informative note: This specification does not limit the size of Informative note: This specification does not limit the size of
NAL units encapsulated in single NAL unit packets and NAL units encapsulated in single NAL unit packets and
fragmentation units. The maximum size of a NAL unit fragmentation units. The maximum size of a NAL unit encapsulated
encapsulated in any aggregation packet is 65535 bytes. in any aggregation packet is 65535 bytes.
Table 1 summarizes NAL unit types and the corresponding RTP packet Table 1 summarizes NAL unit types and the corresponding RTP packet
types when each of these NAL units is directly used as a packet types when each of these NAL units is directly used as a packet
payload, and where the types are described in this memo. payload, and where the types are described in this memo.
Table 1. Summary of NAL unit types and the corresponding packet Table 1. Summary of NAL unit types and the corresponding packet
types types
NAL Unit Packet Packet Type Name Section NAL Unit Packet Packet Type Name Section
Type Type Type Type
--------------------------------------------------------- -------------------------------------------------------------
0 reserved - 0 reserved -
1-23 NAL unit Single NAL unit packet 5.6 1-23 NAL unit Single NAL unit packet 5.6
24 STAP-A Single-time aggregation packet 5.7.1 24 STAP-A Single-time aggregation packet 5.7.1
25 STAP-B Single-time aggregation packet 5.7.1 25 STAP-B Single-time aggregation packet 5.7.1
26 MTAP16 Multi-time aggregation packet 5.7.2 26 MTAP16 Multi-time aggregation packet 5.7.2
27 MTAP24 Multi-time aggregation packet 5.7.2 27 MTAP24 Multi-time aggregation packet 5.7.2
28 FU-A Fragmentation unit 5.8 28 FU-A Fragmentation unit 5.8
29 FU-B Fragmentation unit 5.8 29 FU-B Fragmentation unit 5.8
30-31 reserved - 30-31 reserved -
5.3. NAL Unit Header Usage 5.3. NAL Unit Header Usage
The structure and semantics of the NAL unit header were introduced The structure and semantics of the NAL unit header were introduced in
in section 1.3. For convenience, the format of the NAL unit header Section 1.3. For convenience, the format of the NAL unit header is
is reprinted below: reprinted below:
+---------------+ +---------------+
|0|1|2|3|4|5|6|7| |0|1|2|3|4|5|6|7|
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|F|NRI| Type | |F|NRI| Type |
+---------------+ +---------------+
This section specifies the semantics of F and NRI according to this This section specifies the semantics of F and NRI according to this
specification. specification.
F: 1 bit F: 1 bit
forbidden_zero_bit. A value of 0 indicates that the NAL unit forbidden_zero_bit. A value of 0 indicates that the NAL unit
type octet and payload should not contain bit errors or other type octet and payload should not contain bit errors or other
syntax violations. A value of 1 indicates that the NAL unit syntax violations. A value of 1 indicates that the NAL unit
type octet and payload may contain bit errors or other syntax type octet and payload may contain bit errors or other syntax
violations. violations.
MANEs SHOULD set the F bit to indicate detected bit errors in MANEs SHOULD set the F bit to indicate detected bit errors in
the NAL unit. The H.264 specification requires that the F bit the NAL unit. The H.264 specification requires that the F bit
is equal to 0. When the F bit is set, the decoder is advised be equal to 0. When the F bit is set, the decoder is advised
that bit errors or any other syntax violations may be present in that bit errors or any other syntax violations may be present
the payload or in the NAL unit type octet. The simplest decoder in the payload or in the NAL unit type octet. The simplest
reaction to a NAL unit in which the F bit is equal to 1 is to decoder reaction to a NAL unit in which the F bit is equal to 1
discard such a NAL unit and to conceal the lost data in the is to discard such a NAL unit and to conceal the lost data in
discarded NAL unit. the discarded NAL unit.
NRI: 2 bits NRI: 2 bits
nal_ref_idc. The semantics of value 00 and a non-zero value nal_ref_idc. The semantics of value 00 and a non-zero value
remain unchanged from the H.264 specification. In other words, remain unchanged from the H.264 specification. In other words,
a value of 00 indicates that the content of the NAL unit is not a value of 00 indicates that the content of the NAL unit is not
used to reconstruct reference pictures for inter picture used to reconstruct reference pictures for inter picture
prediction. Such NAL units can be discarded without risking the prediction. Such NAL units can be discarded without risking
integrity of the reference pictures. Values greater than 00 the integrity of the reference pictures. Values greater than
indicate that the decoding of the NAL unit is required to 00 indicate that the decoding of the NAL unit is required to
maintain the integrity of the reference pictures. maintain the integrity of the reference pictures.
In addition to the specification above, according to this RTP In addition to the specification above, according to this RTP
payload specification, values of NRI indicate the relative payload specification, values of NRI indicate the relative
transport priority, as determined by the encoder. MANEs can use transport priority, as determined by the encoder. MANEs can
this information to protect more important NAL units better than use this information to protect more important NAL units better
they do less important NAL units. The highest transport than they do less important NAL units. The highest transport
priority is 11, followed by 10, and then by 01; finally, 00 is priority is 11, followed by 10, and then by 01; finally, 00 is
the lowest. the lowest.
Informative note: Any non-zero value of NRI is handled Informative note: Any non-zero value of NRI is handled
identically in H.264 decoders. Therefore, receivers need not identically in H.264 decoders. Therefore, receivers need
manipulate the value of NRI when passing NAL units to the not manipulate the value of NRI when passing NAL units to
decoder. the decoder.
An H.264 encoder MUST set the value of NRI according to the An H.264 encoder MUST set the value of NRI according to the
H.264 specification (subclause 7.4.1) when the value of H.264 specification (Subclause 7.4.1) when the value of
nal_unit_type is in the range of 1 to 12, inclusive. In nal_unit_type is in the range of 1 to 12, inclusive. In
particular, the H.264 specification requires that the value of particular, the H.264 specification requires that the value of
NRI SHALL be equal to 0 for all NAL units having nal_unit_type NRI SHALL be equal to 0 for all NAL units having nal_unit_type
equal to 6, 9, 10, 11, or 12. equal to 6, 9, 10, 11, or 12.
For NAL units having nal_unit_type equal to 7 or 8 (indicating a For NAL units having nal_unit_type equal to 7 or 8 (indicating
sequence parameter set or a picture parameter set, respectively), a sequence parameter set or a picture parameter set,
an H.264 encoder SHOULD set the value of NRI to 11 (in binary respectively), an H.264 encoder SHOULD set the value of NRI to
format). For coded slice NAL units of a primary coded picture 11 (in binary format). For coded slice NAL units of a primary
having nal_unit_type equal to 5 (indicating a coded slice coded picture having nal_unit_type equal to 5 (indicating a
belonging to an IDR picture), an H.264 encoder SHOULD set the coded slice belonging to an IDR picture), an H.264 encoder
value of NRI to 11 (in binary format). SHOULD set the value of NRI to 11 (in binary format).
For a mapping of the remaining nal_unit_types to NRI values, the For a mapping of the remaining nal_unit_types to NRI values,
following example MAY be used and has been shown to be efficient the following example MAY be used and has been shown to be
in a certain environment [14]. Other mappings MAY also be efficient in a certain environment [14]. Other mappings MAY
desirable, depending on the application and the H.264/AVC Annex also be desirable, depending on the application and the H.264
A profile in use. profile in use.
Informative note: Data Partitioning is not available in Informative note: Data partitioning is not available in
certain profiles; e.g., in the Main or Baseline profiles. certain profiles, e.g., in the Main or Baseline profiles.
Consequently, the NAL unit types 2, 3, and 4 can occur only Consequently, the NAL unit types 2, 3, and 4 can occur only
if the video bitstream conforms to a profile in which data if the video bitstream conforms to a profile in which data
partitioning is allowed and not in streams that conform to partitioning is allowed and not in streams that conform to
the Main or Baseline profiles. the Main or Baseline profiles.
Table 2. Example of NRI values for coded slices and coded slice Table 2. Example of NRI values for coded slices and coded slice
data partitions of primary coded reference pictures data partitions of primary coded reference pictures
NAL Unit Type Content of NAL unit NRI (binary) NAL Unit Type Content of NAL Unit NRI (binary)
---------------------------------------------------------------- ----------------------------------------------------------------
1 non-IDR coded slice 10 1 non-IDR coded slice 10
2 Coded slice data partition A 10 2 Coded slice data partition A 10
3 Coded slice data partition B 01 3 Coded slice data partition B 01
4 Coded slice data partition C 01 4 Coded slice data partition C 01
Informative note: As mentioned before, the NRI value of non- Informative note: As mentioned before, the NRI value of non-
reference pictures is 00 as mandated by H.264/AVC. reference pictures is 00 as mandated by H.264.
An H.264 encoder SHOULD set the value of NRI for coded slice and An H.264 encoder SHOULD set the value of NRI for coded slice
coded slice data partition NAL units of redundant coded and coded slice data partition NAL units of redundant coded
reference pictures equal to 01 (in binary format). reference pictures equal to 01 (in binary format).
Definitions of the values for NRI for NAL unit types 24 to 29, Definitions of the values for NRI for NAL unit types 24 to 29,
inclusive, are given in sections 5.7 and 5.8 of this memo. inclusive, are given in Sections 5.7 and 5.8 of this memo.
No recommendation for the value of NRI is given for NAL units No recommendation for the value of NRI is given for NAL units
having nal_unit_type in the range of 13 to 23, inclusive, having nal_unit_type in the range of 13 to 23, inclusive,
because these values are reserved for ITU-T and ISO/IEC. No because these values are reserved for ITU-T and ISO/IEC. No
recommendation for the value of NRI is given for NAL units recommendation for the value of NRI is given for NAL units
having nal_unit_type equal to 0 or in the range of 30 to 31, having nal_unit_type equal to 0 or in the range of 30 to 31,
inclusive, as the semantics of these values are not specified in inclusive, as the semantics of these values are not specified
this memo. in this memo.
5.4. Packetization Modes 5.4. Packetization Modes
This memo specifies three cases of packetization modes: This memo specifies three cases of packetization modes:
o Single NAL unit mode o Single NAL unit mode
o Non-interleaved mode o Non-interleaved mode
o Interleaved mode o Interleaved mode
The single NAL unit mode is targeted for conversational systems The single NAL unit mode is targeted for conversational systems that
that comply with ITU-T Recommendation H.241 [3] (see section 12.1). comply with ITU-T Recommendation H.241 [3] (see Section 12.1). The
The non-interleaved mode is targeted for conversational systems non-interleaved mode is targeted for conversational systems that may
that may not comply with ITU-T Recommendation H.241. In the non- not comply with ITU-T Recommendation H.241. In the non-interleaved
interleaved mode, NAL units are transmitted in NAL unit decoding mode, NAL units are transmitted in NAL unit decoding order. The
order. The interleaved mode is targeted for systems that do not interleaved mode is targeted for systems that do not require very low
require very low end-to-end latency. The interleaved mode allows end-to-end latency. The interleaved mode allows transmission of NAL
transmission of NAL units out of NAL unit decoding order. units out of NAL unit decoding order.
The packetization mode in use MAY be signaled by the value of the The packetization mode in use MAY be signaled by the value of the
OPTIONAL packetization-mode media type parameter. The used OPTIONAL packetization-mode media type parameter. The used
packetization mode governs which NAL unit types are allowed in RTP packetization mode governs which NAL unit types are allowed in RTP
payloads. Table 3 summarizes the allowed packet payload types for payloads. Table 3 summarizes the allowed packet payload types for
each packetization mode. Packetization modes are explained in more each packetization mode. Packetization modes are explained in more
detail in section 6. detail in Section 6.
Table 3. Summary of allowed NAL unit types for each packetization Table 3. Summary of allowed NAL unit types for each packetization
mode (yes = allowed, no = disallowed, ig = ignore) mode (yes = allowed, no = disallowed, ig = ignore)
Payload Packet Single NAL Non-Interleaved Interleaved Payload Packet Single NAL Non-Interleaved Interleaved
Type Type Unit Mode Mode Mode Type Type Unit Mode Mode Mode
------------------------------------------------------------- -------------------------------------------------------------
0 reserved ig ig ig 0 reserved ig ig ig
1-23 NAL unit yes yes no 1-23 NAL unit yes yes no
24 STAP-A no yes no 24 STAP-A no yes no
25 STAP-B no no yes 25 STAP-B no no yes
26 MTAP16 no no yes 26 MTAP16 no no yes
27 MTAP24 no no yes 27 MTAP24 no no yes
28 FU-A no yes yes 28 FU-A no yes yes
29 FU-B no no yes 29 FU-B no no yes
30-31 reserved ig ig ig 30-31 reserved ig ig ig
Some NAL unit or payload type values (indicated as reserved in Some NAL unit or payload type values (indicated as reserved in Table
Table 3) are reserved for future extensions. NAL units of those 3) are reserved for future extensions. NAL units of those types
types SHOULD NOT be sent by a sender (direct as packet payloads, or SHOULD NOT be sent by a sender (direct as packet payloads, as
as aggregation units in aggregation packets, or as fragmented units aggregation units in aggregation packets, or as fragmented units in
in FU packets) and MUST be ignored by a receiver. For example, the FU packets) and MUST be ignored by a receiver. For example, the
payload types 1-23, with the associated packet type "NAL unit", are payload types 1-23, with the associated packet type "NAL unit", are
allowed in "Single NAL Unit Mode" and in "Non-Interleaved Mode", allowed in "Single NAL Unit Mode" and in "Non-Interleaved Mode" but
but disallowed in "Interleaved Mode". However, NAL units of NAL disallowed in "Interleaved Mode". However, NAL units of NAL unit
unit types 1-23 can be used in "Interleaved Mode" as aggregation types 1-23 can be used in "Interleaved Mode" as aggregation units in
units in STAP-B, MTAP16 and MTAP24 packets as well as fragmented STAP-B, MTAP16, and MTAP24 packets as well as fragmented units in FU-
units in FU-A and FU-B packets. Similarly, NAL units of NAL unit A and FU-B packets. Similarly, NAL units of NAL unit types 1-23 can
types 1-23 can also be used in the "Non-Interleaved Mode" as also be used in the "Non-Interleaved Mode" as aggregation units in
aggregation units in STAP-A packets or fragmented units in FU-A STAP-A packets or fragmented units in FU-A packets, in addition to
packets, in addition to being directly used as packet payloads. being directly used as packet payloads.
5.5. Decoding Order Number (DON) 5.5. Decoding Order Number (DON)
In the interleaved packetization mode, the transmission order of In the interleaved packetization mode, the transmission order of NAL
NAL units is allowed to differ from the decoding order of the NAL units is allowed to differ from the decoding order of the NAL units.
units. Decoding order number (DON) is a field in the payload Decoding order number (DON) is a field in the payload structure or a
structure or a derived variable that indicates the NAL unit derived variable that indicates the NAL unit decoding order.
decoding order. Rationale and examples of use cases for Rationale and examples of use cases for transmission out of decoding
transmission out of decoding order and for the use of DON are given order and for the use of DON are given in Section 13.
in section 13.
The coupling of transmission and decoding order is controlled by The coupling of transmission and decoding order is controlled by the
the OPTIONAL sprop-interleaving-depth media type parameter as OPTIONAL sprop-interleaving-depth media type parameter as follows.
follows. When the value of the OPTIONAL sprop-interleaving-depth When the value of the OPTIONAL sprop-interleaving-depth media type
media type parameter is equal to 0 (explicitly or per default), the parameter is equal to 0 (explicitly or per default), the transmission
transmission order of NAL units MUST conform to the NAL unit order of NAL units MUST conform to the NAL unit decoding order. When
decoding order. When the value of the OPTIONAL sprop-interleaving- the value of the OPTIONAL sprop-interleaving-depth media type
depth media type parameter is greater than 0, parameter is greater than 0:
o the order of NAL units in an MTAP16 and an MTAP24 is not o the order of NAL units in an MTAP16 and an MTAP24 is not required
required to be the NAL unit decoding order, and to be the NAL unit decoding order, and
o the order of NAL units generated by de-packetizing STAP-Bs, o the order of NAL units generated by de-packetizing STAP-Bs, MTAPs,
MTAPs, and FUs in two consecutive packets is not required to be and FUs in two consecutive packets is not required to be the NAL
the NAL unit decoding order. unit decoding order.
The RTP payload structures for a single NAL unit packet, an STAP-A, The RTP payload structures for a single NAL unit packet, an STAP-A,
and an FU-A do not include DON. STAP-B and FU-B structures include and an FU-A do not include DON. STAP-B and FU-B structures include
DON, and the structure of MTAPs enables derivation of DON as DON, and the structure of MTAPs enables derivation of DON, as
specified in section 5.7.2. specified in Section 5.7.2.
Informative note: When an FU-A occurs in interleaved mode, it Informative note: When an FU-A occurs in interleaved mode, it
always follows an FU-B, which sets its DON. always follows an FU-B, which sets its DON.
Informative note: If a transmitter wants to encapsulate a single Informative note: If a transmitter wants to encapsulate a single
NAL unit per packet and transmit packets out of their decoding NAL unit per packet and transmit packets out of their decoding
order, STAP-B packet type can be used. order, STAP-B packet type can be used.
In the single NAL unit packetization mode, the transmission order In the single NAL unit packetization mode, the transmission order of
of NAL units, determined by the RTP sequence number, MUST be the NAL units, determined by the RTP sequence number, MUST be the same as
same as their NAL unit decoding order. In the non-interleaved their NAL unit decoding order. In the non-interleaved packetization
packetization mode, the transmission order of NAL units in single mode, the transmission order of NAL units in single NAL unit packets,
NAL unit packets, STAP-As, and FU-As MUST be the same as their NAL STAP-As, and FU-As MUST be the same as their NAL unit decoding order.
unit decoding order. The NAL units within an STAP MUST appear in The NAL units within an STAP MUST appear in the NAL unit decoding
the NAL unit decoding order. Thus, the decoding order is first order. Thus, the decoding order is first provided through the
provided through the implicit order within a STAP, and second implicit order within an STAP and then provided through the RTP
provided through the RTP sequence number for the order between sequence number for the order between STAPs, FUs, and single NAL unit
STAPs, FUs, and single NAL unit packets. packets.
Signaling of the value of DON for NAL units carried in STAP-B, MTAP, The signaling of the value of DON for NAL units carried in STAP-B,
and a series of fragmentation units starting with an FU-B is MTAP, and a series of fragmentation units starting with an FU-B is
specified in sections 5.7.1, 5.7.2, and 5.8, respectively. The DON specified in Sections 5.7.1, 5.7.2, and 5.8, respectively. The DON
value of the first NAL unit in transmission order MAY be set to any value of the first NAL unit in transmission order MAY be set to any
value. Values of DON are in the range of 0 to 65535, inclusive. value. Values of DON are in the range of 0 to 65535, inclusive.
After reaching the maximum value, the value of DON wraps around to After reaching the maximum value, the value of DON wraps around to 0.
0.
The decoding order of two NAL units contained in any STAP-B, MTAP, The decoding order of two NAL units contained in any STAP-B, MTAP, or
or a series of fragmentation units starting with an FU-B is a series of fragmentation units starting with an FU-B is determined
determined as follows. Let DON(i) be the decoding order number of as follows. Let DON(i) be the decoding order number of the NAL unit
the NAL unit having index i in the transmission order. Function having index i in the transmission order. Function don_diff(m,n) is
don_diff(m,n) is specified as follows: specified as follows:
If DON(m) == DON(n), don_diff(m,n) = 0 If DON(m) == DON(n), don_diff(m,n) = 0
If (DON(m) < DON(n) and DON(n) - DON(m) < 32768), If (DON(m) < DON(n) and DON(n) - DON(m) < 32768),
don_diff(m,n) = DON(n) - DON(m) don_diff(m,n) = DON(n) - DON(m)
If (DON(m) > DON(n) and DON(m) - DON(n) >= 32768), If (DON(m) > DON(n) and DON(m) - DON(n) >= 32768),
don_diff(m,n) = 65536 - DON(m) + DON(n) don_diff(m,n) = 65536 - DON(m) + DON(n)
If (DON(m) < DON(n) and DON(n) - DON(m) >= 32768), If (DON(m) < DON(n) and DON(n) - DON(m) >= 32768),
don_diff(m,n) = - (DON(m) + 65536 - DON(n)) don_diff(m,n) = - (DON(m) + 65536 - DON(n))
If (DON(m) > DON(n) and DON(m) - DON(n) < 32768), If (DON(m) > DON(n) and DON(m) - DON(n) < 32768),
don_diff(m,n) = - (DON(m) - DON(n)) don_diff(m,n) = - (DON(m) - DON(n))
A positive value of don_diff(m,n) indicates that the NAL unit A positive value of don_diff(m,n) indicates that the NAL unit having
having transmission order index n follows, in decoding order, the transmission order index n follows, in decoding order, the NAL unit
NAL unit having transmission order index m. When don_diff(m,n) is having transmission order index m. When don_diff(m,n) is equal to 0,
equal to 0, then the NAL unit decoding order of the two NAL units the NAL unit decoding order of the two NAL units can be in either
can be in either order. A negative value of don_diff(m,n) order. A negative value of don_diff(m,n) indicates that the NAL unit
indicates that the NAL unit having transmission order index n having transmission order index n precedes, in decoding order, the
precedes, in decoding order, the NAL unit having transmission order NAL unit having transmission order index m.
index m.
Values of DON related fields (DON, DONB, and DOND; see section 5.7) Values of DON-related fields (DON, DONB, and DOND; see Section 5.7)
MUST be such that the decoding order determined by the values of MUST be such that the decoding order determined by the values of DON,
DON, as specified above, conforms to the NAL unit decoding order. as specified above, conforms to the NAL unit decoding order.
If the order of two NAL units in NAL unit decoding order is If the order of two NAL units in NAL unit decoding order is switched
switched and the new order does not conform to the NAL unit and the new order does not conform to the NAL unit decoding order,
decoding order, the NAL units MUST NOT have the same value of DON. the NAL units MUST NOT have the same value of DON. If the order of
If the order of two consecutive NAL units in the NAL unit stream is two consecutive NAL units in the NAL unit stream is switched and the
switched and the new order still conforms to the NAL unit decoding new order still conforms to the NAL unit decoding order, the NAL
order, the NAL units MAY have the same value of DON. For example, units MAY have the same value of DON. For example, when arbitrary
when arbitrary slice order is allowed by the video coding profile slice order is allowed by the video coding profile in use, all the
in use, all the coded slice NAL units of a coded picture are coded slice NAL units of a coded picture are allowed to have the same
allowed to have the same value of DON. Consequently, NAL units value of DON. Consequently, NAL units having the same value of DON
having the same value of DON can be decoded in any order, and two can be decoded in any order, and two NAL units having a different
NAL units having a different value of DON should be passed to the value of DON should be passed to the decoder in the order specified
decoder in the order specified above. When two consecutive NAL above. When two consecutive NAL units in the NAL unit decoding order
units in the NAL unit decoding order have a different value of DON, have a different value of DON, the value of DON for the second NAL
the value of DON for the second NAL unit in decoding order SHOULD unit in decoding order SHOULD be the value of DON for the first,
be the value of DON for the first, incremented by one. incremented by one.
An example of the de-packetization process to recover the NAL unit An example of the de-packetization process to recover the NAL unit
decoding order is given in section 7. decoding order is given in Section 7.
Informative note: Receivers should not expect that the absolute Informative note: Receivers should not expect that the absolute
difference of values of DON for two consecutive NAL units in the difference of values of DON for two consecutive NAL units in the
NAL unit decoding order will be equal to one, even in error-free NAL unit decoding order will be equal to one, even in error-free
transmission. An increment by one is not required, as at the transmission. An increment by one is not required, as at the time
time of associating values of DON to NAL units, it may not be of associating values of DON to NAL units, it may not be known
known whether all NAL units are delivered to the receiver. For whether all NAL units are delivered to the receiver. For example,
example, a gateway may not forward coded slice NAL units of non- a gateway may not forward coded slice NAL units of non-reference
reference pictures or SEI NAL units when there is a shortage of pictures or SEI NAL units when there is a shortage of bitrate in
bit rate in the network to which the packets are forwarded. In the network to which the packets are forwarded. In another
another example, a live broadcast is interrupted by pre-encoded example, a live broadcast is interrupted by pre-encoded content,
content, such as commercials, from time to time. The first such as commercials, from time to time. The first intra picture
intra picture of a pre-encoded clip is transmitted in advance to of a pre-encoded clip is transmitted in advance to ensure that it
ensure that it is readily available in the receiver. When is readily available in the receiver. When transmitting the first
transmitting the first intra picture, the originator does not intra picture, the originator does not exactly know how many NAL
exactly know how many NAL units will be encoded before the first units will be encoded before the first intra picture of the pre-
intra picture of the pre-encoded clip follows in decoding order. encoded clip follows in decoding order. Thus, the values of DON
Thus, the values of DON for the NAL units of the first intra for the NAL units of the first intra picture of the pre-encoded
picture of the pre-encoded clip have to be estimated when they clip have to be estimated when they are transmitted, and gaps in
are transmitted, and gaps in values of DON may occur. values of DON may occur.
5.6. Single NAL Unit Packet 5.6. Single NAL Unit Packet
The single NAL unit packet defined here MUST contain only one NAL The single NAL unit packet defined here MUST contain only one NAL
unit, of the types defined in [1]. This means that neither an unit of the types defined in [1]. This means that neither an
aggregation packet nor a fragmentation unit can be used within a aggregation packet nor a fragmentation unit can be used within a
single NAL unit packet. A NAL unit stream composed by de- single NAL unit packet. A NAL unit stream composed by de-packetizing
packetizing single NAL unit packets in RTP sequence number order single NAL unit packets in RTP sequence number order MUST conform to
MUST conform to the NAL unit decoding order. The structure of the the NAL unit decoding order. The structure of the single NAL unit
single NAL unit packet is shown in Figure 2. packet is shown in Figure 2.
Informative note: The first byte of a NAL unit co-serves as the Informative note: The first byte of a NAL unit co-serves as the
RTP payload header. RTP payload header.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|NRI| Type | | |F|NRI| Type | |
+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+ |
| | | |
| Bytes 2..n of a Single NAL unit | | Bytes 2..n of a single NAL unit |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding | | :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2 RTP payload format for single NAL unit packet Figure 2. RTP payload format for single NAL unit packet
5.7. Aggregation Packets 5.7. Aggregation Packets
Aggregation packets are the NAL unit aggregation scheme of this Aggregation packets are the NAL unit aggregation scheme of this
payload specification. The scheme is introduced to reflect the payload specification. The scheme is introduced to reflect the
dramatically different MTU sizes of two key target networks: dramatically different MTU sizes of two key target networks: wireline
wireline IP networks (with an MTU size that is often limited by the IP networks (with an MTU size that is often limited by the Ethernet
Ethernet MTU size; roughly 1500 bytes), and IP or non-IP (e.g., MTU size, roughly 1500 bytes) and IP-based or non-IP-based (e.g.,
ITU-T H.324/M) based wireless communication systems with preferred ITU-T H.324/M) wireless communication systems with preferred
transmission unit sizes of 254 bytes or less. To prevent media transmission unit sizes of 254 bytes or less. To prevent media
transcoding between the two worlds, and to avoid undesirable transcoding between the two worlds, and to avoid undesirable
packetization overhead, a NAL unit aggregation scheme is introduced. packetization overhead, a NAL unit aggregation scheme is introduced.
Two types of aggregation packets are defined by this specification: Two types of aggregation packets are defined by this specification:
o Single-time aggregation packet (STAP): aggregates NAL units with o Single-time aggregation packet (STAP): aggregates NAL units with
identical NALU-time. Two types of STAPs are defined, one identical NALU-times. Two types of STAPs are defined, one without
without DON (STAP-A) and another including DON (STAP-B). DON (STAP-A) and another including DON (STAP-B).
o Multi-time aggregation packet (MTAP): aggregates NAL units with o Multi-time aggregation packet (MTAP): aggregates NAL units with
potentially differing NALU-time. Two different MTAPs are potentially differing NALU-times. Two different MTAPs are
defined, differing in the length of the NAL unit timestamp defined, differing in the length of the NAL unit timestamp offset.
offset.
Each NAL unit to be carried in an aggregation packet is Each NAL unit to be carried in an aggregation packet is encapsulated
encapsulated in an aggregation unit. Please see below for the four in an aggregation unit. Please see below for the four different
different aggregation units and their characteristics. aggregation units and their characteristics.
The structure of the RTP payload format for aggregation packets is The structure of the RTP payload format for aggregation packets is
presented in Figure 3. presented in Figure 3.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|NRI| Type | | |F|NRI| Type | |
+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+ |
| | | |
| one or more aggregation units | | one or more aggregation units |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding | | :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3 RTP payload format for aggregation packets Figure 3. RTP payload format for aggregation packets
MTAPs and STAPs share the following packetization rules: The RTP MTAPs and STAPs share the following packetization rules:
timestamp MUST be set to the earliest of the NALU-times of all the
NAL units to be aggregated. The type field of the NAL unit type o The RTP timestamp MUST be set to the earliest of the NALU-times of
octet MUST be set to the appropriate value, as indicated in Table 4. all the NAL units to be aggregated.
The F bit MUST be cleared if all F bits of the aggregated NAL units
are zero; otherwise, it MUST be set. The value of NRI MUST be the o The type field of the NAL unit type octet MUST be set to the
maximum of all the NAL units carried in the aggregation packet. appropriate value, as indicated in Table 4.
o The F bit MUST be cleared if all F bits of the aggregated NAL
units are zero; otherwise, it MUST be set.
o The value of NRI MUST be the maximum of all the NAL units carried
in the aggregation packet.
Table 4. Type field for STAPs and MTAPs Table 4. Type field for STAPs and MTAPs
Type Packet Timestamp offset DON related fields Type Packet Timestamp offset DON-related fields
field length (DON, DONB, DOND) field length (DON, DONB, DOND)
(in bits) present (in bits) present
-------------------------------------------------------- --------------------------------------------------------
24 STAP-A 0 no 24 STAP-A 0 no
25 STAP-B 0 yes 25 STAP-B 0 yes
26 MTAP16 16 yes 26 MTAP16 16 yes
27 MTAP24 24 yes 27 MTAP24 24 yes
The marker bit in the RTP header is set to the value that the The marker bit in the RTP header is set to the value that the marker
marker bit of the last NAL unit of the aggregated packet would have bit of the last NAL unit of the aggregated packet would have if it
if it were transported in its own RTP packet. were transported in its own RTP packet.
The payload of an aggregation packet consists of one or more The payload of an aggregation packet consists of one or more
aggregation units. See sections 5.7.1 and 5.7.2 for the four aggregation units. See Sections 5.7.1 and 5.7.2 for the four
different types of aggregation units. An aggregation packet can different types of aggregation units. An aggregation packet can
carry as many aggregation units as necessary; however, the total carry as many aggregation units as necessary; however, the total
amount of data in an aggregation packet obviously MUST fit into an amount of data in an aggregation packet obviously MUST fit into an IP
IP packet, and the size SHOULD be chosen so that the resulting IP packet, and the size SHOULD be chosen so that the resulting IP packet
packet is smaller than the MTU size. An aggregation packet MUST is smaller than the MTU size. An aggregation packet MUST NOT contain
NOT contain fragmentation units specified in section 5.8. fragmentation units, as specified in Section 5.8. Aggregation
Aggregation packets MUST NOT be nested; i.e., an aggregation packet packets MUST NOT be nested; that is, an aggregation packet MUST NOT
MUST NOT contain another aggregation packet. contain another aggregation packet.
5.7.1. Single-Time Aggregation Packet
Single-time aggregation packet (STAP) SHOULD be used whenever NAL 5.7.1. Single-Time Aggregation Packet (STAP)
units are aggregated that all share the same NALU-time. The
payload of an STAP-A does not include DON and consists of at least
one single-time aggregation unit, as presented in Figure 4. The
payload of an STAP-B consists of a 16-bit unsigned decoding order
number (DON) (in network byte order) followed by at least one
single-time aggregation unit, as presented in Figure 5.
0 1 2 3 A single-time aggregation packet (STAP) SHOULD be used whenever NAL
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 units are aggregated that all share the same NALU-time. The payload
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ of an STAP-A does not include DON and consists of at least one
: | single-time aggregation unit, as presented in Figure 4. The payload
+-+-+-+-+-+-+-+-+ | of an STAP-B consists of a 16-bit unsigned decoding order number
| | (DON) (in network byte order) followed by at least one single-time
| single-time aggregation units | aggregation unit, as presented in Figure 5.
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4 Payload format for STAP-A 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: |
+-+-+-+-+-+-+-+-+ |
| |
| single-time aggregation units |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3 Figure 4. Payload format for STAP-A
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
: decoding order number (DON) | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | : decoding order number (DON) | |
| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| single-time aggregation units | | |
| | | single-time aggregation units |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| : | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5 Payload format for STAP-B Figure 5. Payload format for STAP-B
The DON field specifies the value of DON for the first NAL unit in The DON field specifies the value of DON for the first NAL unit in an
an STAP-B in transmission order. For each successive NAL unit in STAP-B in transmission order. For each successive NAL unit in
appearance order in an STAP-B, the value of DON is equal to (the appearance order in an STAP-B, the value of DON is equal to (the
value of DON of the previous NAL unit in the STAP-B + 1) % 65536, value of DON of the previous NAL unit in the STAP-B + 1) % 65536, in
in which '%' stands for the modulo operation. which '%' stands for the modulo operation.
A single-time aggregation unit consists of 16-bit unsigned size A single-time aggregation unit consists of 16-bit unsigned size
information (in network byte order) that indicates the size of the information (in network byte order) that indicates the size of the
following NAL unit in bytes (excluding these two octets, but following NAL unit in bytes (excluding these two octets, but
including the NAL unit type octet of the NAL unit), followed by the including the NAL unit type octet of the NAL unit), followed by the
NAL unit itself, including its NAL unit type byte. A single-time NAL unit itself, including its NAL unit type byte. A single-time
aggregation unit is byte aligned within the RTP payload, but it may aggregation unit is byte aligned within the RTP payload, but it may
not be aligned on a 32-bit word boundary. Figure 6 presents the not be aligned on a 32-bit word boundary. Figure 6 presents the
structure of the single-time aggregation unit. structure of the single-time aggregation unit.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: NAL unit size | | : NAL unit size | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
| NAL unit | | NAL unit |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : | :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6 Structure for single-time aggregation unit Figure 6. Structure for single-time aggregation unit
Figure 7 presents an example of an RTP packet that contains an Figure 7 presents an example of an RTP packet that contains an STAP-
STAP-A. The STAP contains two single-time aggregation units, A. The STAP contains two single-time aggregation units, labeled as 1
labeled as 1 and 2 in the figure. and 2 in the figure.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTP Header | | RTP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|STAP-A NAL HDR | NALU 1 Size | NALU 1 HDR | |STAP-A NAL HDR | NALU 1 Size | NALU 1 HDR |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 1 Data | | NALU 1 Data |
: : : :
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | NALU 2 Size | NALU 2 HDR | | | NALU 2 Size | NALU 2 HDR |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 2 Data | | NALU 2 Data |
: : : :
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding | | :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7 An example of an RTP packet including an STAP-A containing Figure 7. An example of an RTP packet including an STAP-A
two single-time aggregation units containing two single-time aggregation units
Figure 8 presents an example of an RTP packet that contains an Figure 8 presents an example of an RTP packet that contains an STAP-
STAP-B. The STAP contains two single-time aggregation units, B. The STAP contains two single-time aggregation units, labeled as 1
labeled as 1 and 2 in the figure. and 2 in the figure.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTP Header | | RTP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|STAP-B NAL HDR | DON | NALU 1 Size | |STAP-B NAL HDR | DON | NALU 1 Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 1 Size | NALU 1 HDR | NALU 1 Data | | NALU 1 Size | NALU 1 HDR | NALU 1 Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
: : : :
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | NALU 2 Size | NALU 2 HDR | | | NALU 2 Size | NALU 2 HDR |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 2 Data | | NALU 2 Data |
: : : :
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding | | :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8 An example of an RTP packet including an STAP-B containing Figure 8. An example of an RTP packet including an STAP-B
two single-time aggregation units containing two single-time aggregation units
5.7.2. Multi-Time Aggregation Packets (MTAPs) 5.7.2. Multi-Time Aggregation Packets (MTAPs)
The NAL unit payload of MTAPs consists of a 16-bit unsigned The NAL unit payload of MTAPs consists of a 16-bit unsigned decoding
decoding order number base (DONB) (in network byte order) and one order number base (DONB) (in network byte order) and one or more
or more multi-time aggregation units, as presented in Figure 9. multi-time aggregation units, as presented in Figure 9. DONB MUST
DONB MUST contain the value of DON for the first NAL unit in the contain the value of DON for the first NAL unit in the NAL unit
NAL unit decoding order among the NAL units of the MTAP. decoding order among the NAL units of the MTAP.
Informative note: The first NAL unit in the NAL unit decoding Informative note: The first NAL unit in the NAL unit decoding
order is not necessarily the first NAL unit in the order in order is not necessarily the first NAL unit in the order in which
which the NAL units are encapsulated in an MTAP. the NAL units are encapsulated in an MTAP.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: decoding order number base | | : decoding order number base | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
| multi-time aggregation units | | multi-time aggregation units |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : | :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9 NAL unit payload format for MTAPs Figure 9. NAL unit payload format for MTAPs
Two different multi-time aggregation units are defined in this Two different multi-time aggregation units are defined in this
specification. Both of them consist of 16 bits unsigned size specification. Both of them consist of 16 bits of unsigned size
information of the following NAL unit (in network byte order), an information of the following NAL unit (in network byte order), an
8-bit unsigned decoding order number difference (DOND), and n bits 8-bit unsigned decoding order number difference (DOND), and n bits
(in network byte order) of timestamp offset (TS offset) for this (in network byte order) of timestamp offset (TS offset) for this NAL
NAL unit, whereby n can be 16 or 24. The choice between the unit, whereby n can be 16 or 24. The choice between the different
different MTAP types (MTAP16 and MTAP24) is application dependent: MTAP types (MTAP16 and MTAP24) is application dependent: the larger
the larger the timestamp offset is, the higher the flexibility of the timestamp offset is, the higher the flexibility of the MTAP, but
the MTAP, but the overhead is also higher. the overhead is also higher.
The structure of the multi-time aggregation units for MTAP16 and The structure of the multi-time aggregation units for MTAP16 and
MTAP24 are presented in Figures 10 and 11, respectively. The MTAP24 are presented in Figures 10 and 11, respectively. The
starting or ending position of an aggregation unit within a packet starting or ending position of an aggregation unit within a packet is
is not required to be on a 32-bit word boundary. The DON of the not required to be on a 32-bit word boundary. The DON of the NAL
NAL unit contained in a multi-time aggregation unit is equal to unit contained in a multi-time aggregation unit is equal to (DONB +
(DONB + DOND) % 65536, in which % denotes the modulo operation. DOND) % 65536, in which % denotes the modulo operation. This memo
This memo does not specify how the NAL units within an MTAP are does not specify how the NAL units within an MTAP are ordered, but,
ordered, but, in most cases, NAL unit decoding order SHOULD be used. in most cases, NAL unit decoding order SHOULD be used.
The timestamp offset field MUST be set to a value equal to the The timestamp offset field MUST be set to a value equal to the value
value of the following formula: If the NALU-time is larger than or of the following formula: if the NALU-time is larger than or equal to
equal to the RTP timestamp of the packet, then the timestamp offset the RTP timestamp of the packet, then the timestamp offset equals
equals (the NALU-time of the NAL unit - the RTP timestamp of the (the NALU-time of the NAL unit - the RTP timestamp of the packet).
packet). If the NALU-time is smaller than the RTP timestamp of the If the NALU-time is smaller than the RTP timestamp of the packet,
packet, then the timestamp offset is equal to the NALU-time + (2^32 then the timestamp offset is equal to the NALU-time + (2^32 - the RTP
- the RTP timestamp of the packet). timestamp of the packet).
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: NAL unit size | DOND | TS offset | : NAL unit size | DOND | TS offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TS offset | | | TS offset | |
+-+-+-+-+-+-+-+-+ NAL unit | +-+-+-+-+-+-+-+-+ NAL unit |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : | :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10 Multi-time aggregation unit for MTAP16 Figure 10. Multi-time aggregation unit for MTAP16
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: NAL unit size | DOND | TS offset | : NAL unit size | DOND | TS offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TS offset | | | TS offset | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| NAL unit | | NAL unit |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : | :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11 Multi-time aggregation unit for MTAP24 Figure 11. Multi-time aggregation unit for MTAP24
For the "earliest" multi-time aggregation unit in an MTAP the For the "earliest" multi-time aggregation unit in an MTAP, the
timestamp offset MUST be zero. Hence, the RTP timestamp of the timestamp offset MUST be zero. Hence, the RTP timestamp of the MTAP
MTAP itself is identical to the earliest NALU-time. itself is identical to the earliest NALU-time.
Informative note: The "earliest" multi-time aggregation unit is Informative note: The "earliest" multi-time aggregation unit is
the one that would have the smallest extended RTP timestamp the one that would have the smallest extended RTP timestamp among
among all the aggregation units of an MTAP if the NAL units all the aggregation units of an MTAP if the NAL units contained in
contained in the aggregation units were encapsulated in single the aggregation units were encapsulated in single NAL unit
NAL unit packets. An extended timestamp is a timestamp that has packets. An extended timestamp is a timestamp that has more than
more than 32 bits and is capable of counting the wraparound of 32 bits and is capable of counting the wraparound of the timestamp
the timestamp field, thus enabling one to determine the smallest field, thus enabling one to determine the smallest value if the
value if the timestamp wraps. Such an "earliest" aggregation timestamp wraps. Such an "earliest" aggregation unit may not be
unit may not be the first one in the order in which the the first one in the order in which the aggregation units are
aggregation units are encapsulated in an MTAP. The "earliest" encapsulated in an MTAP. The "earliest" NAL unit need not be the
NAL unit need not be the same as the first NAL unit in the NAL same as the first NAL unit in the NAL unit decoding order either.
unit decoding order either.
Figure 12 presents an example of an RTP packet that contains a Figure 12 presents an example of an RTP packet that contains a multi-
multi-time aggregation packet of type MTAP16 that contains two time aggregation packet of type MTAP16 that contains two multi-time
multi-time aggregation units, labeled as 1 and 2 in the figure. aggregation units, labeled as 1 and 2 in the figure.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTP Header | | RTP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MTAP16 NAL HDR | decoding order number base | NALU 1 Size | |MTAP16 NAL HDR | decoding order number base | NALU 1 Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 1 Size | NALU 1 DOND | NALU 1 TS offset | | NALU 1 Size | NALU 1 DOND | NALU 1 TS offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 1 HDR | NALU 1 DATA | | NALU 1 HDR | NALU 1 DATA |
+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+ +
: : : :
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | NALU 2 SIZE | NALU 2 DOND | | | NALU 2 SIZE | NALU 2 DOND |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 2 TS offset | NALU 2 HDR | NALU 2 DATA | | NALU 2 TS offset | NALU 2 HDR | NALU 2 DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
: : : :
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding | | :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12 An RTP packet including a multi-time aggregation packet Figure 12. An RTP packet including a multi-time aggregation
of type MTAP16 containing two multi-time aggregation units packet of type MTAP16 containing two multi-time
aggregation units
Figure 13 presents an example of an RTP packet that contains a Figure 13 presents an example of an RTP packet that contains a multi-
multi-time aggregation packet of type MTAP24 that contains two time aggregation packet of type MTAP24 that contains two multi-time
multi-time aggregation units, labeled as 1 and 2 in the figure. aggregation units, labeled as 1 and 2 in the figure.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTP Header | | RTP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MTAP24 NAL HDR | decoding order number base | NALU 1 Size | |MTAP24 NAL HDR | decoding order number base | NALU 1 Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 1 Size | NALU 1 DOND | NALU 1 TS offs | | NALU 1 Size | NALU 1 DOND | NALU 1 TS offs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|NALU 1 TS offs | NALU 1 HDR | NALU 1 DATA | |NALU 1 TS offs | NALU 1 HDR | NALU 1 DATA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
: : : :
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | NALU 2 SIZE | NALU 2 DOND | | | NALU 2 SIZE | NALU 2 DOND |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 2 TS offset | NALU 2 HDR | | NALU 2 TS offset | NALU 2 HDR |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 2 DATA | | NALU 2 DATA |
: : : :
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding | | :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13 An RTP packet including a multi-time aggregation packet Figure 13. An RTP packet including a multi-time aggregation
of type MTAP24 containing two multi-time aggregation units packet of type MTAP24 containing two multi-time
aggregation units
5.7.3. Fragmentation Units (FUs) 5.8. Fragmentation Units (FUs)
This payload type allows fragmenting a NAL unit into several RTP This payload type allows fragmenting a NAL unit into several RTP
packets. Doing so on the application layer instead of relying on packets. Doing so on the application layer instead of relying on
lower layer fragmentation (e.g., by IP) has the following lower-layer fragmentation (e.g., by IP) has the following advantages:
advantages:
o The payload format is capable of transporting NAL units bigger o The payload format is capable of transporting NAL units bigger
than 64 kbytes over an IPv4 network that may be present in pre- than 64 kbytes over an IPv4 network that may be present in pre-
recorded video, particularly in High Definition formats (there recorded video, particularly in High-Definition formats (there is
is a limit of the number of slices per picture, which results in a limit of the number of slices per picture, which results in a
a limit of NAL units per picture, which may result in big NAL limit of NAL units per picture, which may result in big NAL
units). units).
o The fragmentation mechanism allows fragmenting a single NAL unit o The fragmentation mechanism allows fragmenting a single NAL unit
and applying generic forward error correction as described in and applying generic forward error correction as described in
section 12.5. Section 12.5.
Fragmentation is defined only for a single NAL unit and not for any Fragmentation is defined only for a single NAL unit and not for any
aggregation packets. A fragment of a NAL unit consists of an aggregation packets. A fragment of a NAL unit consists of an integer
integer number of consecutive octets of that NAL unit. Each octet number of consecutive octets of that NAL unit. Each octet of the NAL
of the NAL unit MUST be part of exactly one fragment of that NAL unit MUST be part of exactly one fragment of that NAL unit.
unit. Fragments of the same NAL unit MUST be sent in consecutive Fragments of the same NAL unit MUST be sent in consecutive order with
order with ascending RTP sequence numbers (with no other RTP ascending RTP sequence numbers (with no other RTP packets within the
packets within the same RTP packet stream being sent between the same RTP packet stream being sent between the first and last
first and last fragment). Similarly, a NAL unit MUST be fragment). Similarly, a NAL unit MUST be reassembled in RTP sequence
reassembled in RTP sequence number order. number order.
When a NAL unit is fragmented and conveyed within fragmentation When a NAL unit is fragmented and conveyed within fragmentation units
units (FUs), it is referred to as a fragmented NAL unit. STAPs and (FUs), it is referred to as a fragmented NAL unit. STAPs and MTAPs
MTAPs MUST NOT be fragmented. FUs MUST NOT be nested; i.e., an FU MUST NOT be fragmented. FUs MUST NOT be nested; that is, an FU MUST
MUST NOT contain another FU. NOT contain another FU.
The RTP timestamp of an RTP packet carrying an FU is set to the The RTP timestamp of an RTP packet carrying an FU is set to the NALU-
NALU-time of the fragmented NAL unit. time of the fragmented NAL unit.
Figure 14 presents the RTP payload format for FU-As. An FU-A Figure 14 presents the RTP payload format for FU-As. An FU-A
consists of a fragmentation unit indicator of one octet, a consists of a fragmentation unit indicator of one octet, a
fragmentation unit header of one octet, and a fragmentation unit fragmentation unit header of one octet, and a fragmentation unit
payload. payload.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FU indicator | FU header | | | FU indicator | FU header | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
| FU payload | | FU payload |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding | | :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14 RTP payload format for FU-A Figure 14. RTP payload format for FU-A
Figure 15 presents the RTP payload format for FU-Bs. An FU-B Figure 15 presents the RTP payload format for FU-Bs. An FU-B
consists of a fragmentation unit indicator of one octet, a consists of a fragmentation unit indicator of one octet, a
fragmentation unit header of one octet, a decoding order number fragmentation unit header of one octet, a decoding order number (DON)
(DON) (in network byte order), and a fragmentation unit payload. (in network byte order), and a fragmentation unit payload. In other
In other words, the structure of FU-B is the same as the structure words, the structure of FU-B is the same as the structure of FU-A,
of FU-A, except for the additional DON field. except for the additional DON field.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FU indicator | FU header | DON | | FU indicator | FU header | DON |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| | | |
| FU payload | | FU payload |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding | | :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15 RTP payload format for FU-B Figure 15. RTP payload format for FU-B
NAL unit type FU-B MUST be used in the interleaved packetization NAL unit type FU-B MUST be used in the interleaved packetization mode
mode for the first fragmentation unit of a fragmented NAL unit. for the first fragmentation unit of a fragmented NAL unit. NAL unit
NAL unit type FU-B MUST NOT be used in any other case. In other type FU-B MUST NOT be used in any other case. In other words, in the
words, in the interleaved packetization mode, each NALU that is interleaved packetization mode, each NALU that is fragmented has an
fragmented has an FU-B as the first fragment, followed by one or FU-B as the first fragment, followed by one or more FU-A fragments.
more FU-A fragments.
The FU indicator octet has the following format: The FU indicator octet has the following format:
+---------------+ +---------------+
|0|1|2|3|4|5|6|7| |0|1|2|3|4|5|6|7|
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|F|NRI| Type | |F|NRI| Type |
+---------------+ +---------------+
Values equal to 28 and 29 in the Type field of the FU indicator Values equal to 28 and 29 in the type field of the FU indicator octet
octet identify an FU-A and an FU-B, respectively. The use of the F identify an FU-A and an FU-B, respectively. The use of the F bit is
bit is described in section 5.3. The value of the NRI field MUST described in Section 5.3. The value of the NRI field MUST be set
be set according to the value of the NRI field in the fragmented according to the value of the NRI field in the fragmented NAL unit.
NAL unit.
The FU header has the following format: The FU header has the following format:
+---------------+ +---------------+
|0|1|2|3|4|5|6|7| |0|1|2|3|4|5|6|7|
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|S|E|R| Type | |S|E|R| Type |
+---------------+ +---------------+
S: 1 bit S: 1 bit
When set to one, the Start bit indicates the start of a When set to one, the Start bit indicates the start of a
fragmented NAL unit. When the following FU payload is not the fragmented NAL unit. When the following FU payload is not the
start of a fragmented NAL unit payload, the Start bit is set to start of a fragmented NAL unit payload, the Start bit is set
zero. to zero.
E: 1 bit E: 1 bit
When set to one, the End bit indicates the end of a fragmented When set to one, the End bit indicates the end of a fragmented
NAL unit, i.e., the last byte of the payload is also the last NAL unit, i.e., the last byte of the payload is also the last
byte of the fragmented NAL unit. When the following FU payload byte of the fragmented NAL unit. When the following FU
is not the last fragment of a fragmented NAL unit, the End bit payload is not the last fragment of a fragmented NAL unit, the
is set to zero. End bit is set to zero.
R: 1 bit R: 1 bit
The Reserved bit MUST be equal to 0 and MUST be ignored by the The Reserved bit MUST be equal to 0 and MUST be ignored by the
receiver. receiver.
Type: 5 bits Type: 5 bits
The NAL unit payload type as defined in Table 7-1 of [1]. The NAL unit payload type as defined in Table 7-1 of [1].
The value of DON in FU-Bs is selected as described in section 5.5. The value of DON in FU-Bs is selected as described in Section 5.5.
Informative note: The DON field in FU-Bs allows gateways to Informative note: The DON field in FU-Bs allows gateways to
fragment NAL units to FU-Bs without organizing the incoming NAL fragment NAL units to FU-Bs without organizing the incoming NAL
units to the NAL unit decoding order. units to the NAL unit decoding order.
A fragmented NAL unit MUST NOT be transmitted in one FU; i.e., the A fragmented NAL unit MUST NOT be transmitted in one FU; that is, the
Start bit and End bit MUST NOT both be set to one in the same FU Start bit and End bit MUST NOT both be set to one in the same FU
header. header.
The FU payload consists of fragments of the payload of the The FU payload consists of fragments of the payload of the fragmented
fragmented NAL unit so that if the fragmentation unit payloads of NAL unit so that if the fragmentation unit payloads of consecutive
consecutive FUs are sequentially concatenated, the payload of the FUs are sequentially concatenated, the payload of the fragmented NAL
fragmented NAL unit can be reconstructed. The NAL unit type octet unit can be reconstructed. The NAL unit type octet of the fragmented
of the fragmented NAL unit is not included as such in the NAL unit is not included as such in the fragmentation unit payload,
fragmentation unit payload, but rather the information of the NAL but rather the information of the NAL unit type octet of the
unit type octet of the fragmented NAL unit is conveyed in F and NRI fragmented NAL unit is conveyed in the F and NRI fields of the FU
fields of the FU indicator octet of the fragmentation unit and in indicator octet of the fragmentation unit and in the type field of
the type field of the FU header. An FU payload MAY have any number the FU header. An FU payload MAY have any number of octets and MAY
of octets and MAY be empty. be empty.
Informative note: Empty FUs are allowed to reduce the latency of Informative note: Empty FUs are allowed to reduce the latency of a
a certain class of senders in nearly lossless environments. certain class of senders in nearly lossless environments. These
These senders can be characterized in that they packetize NALU senders can be characterized in that they packetize NALU fragments
fragments before the NALU is completely generated and, hence, before the NALU is completely generated and, hence, before the
before the NALU size is known. If zero-length NALU fragments NALU size is known. If zero-length NALU fragments were not
were not allowed, the sender would have to generate at least one allowed, the sender would have to generate at least one bit of
bit of data of the following fragment before the current data of the following fragment before the current fragment could
fragment could be sent. Due to the characteristics of H.264, be sent. Due to the characteristics of H.264, where sometimes
where sometimes several macroblocks occupy zero bits, this is several macroblocks occupy zero bits, this is undesirable and can
undesirable and can add delay. However, the (potential) use of add delay. However, the (potential) use of zero-length NALU
zero-length NALU fragments should be carefully weighed against fragments should be carefully weighed against the increased risk
the increased risk of the loss of at least a part of the NALU of the loss of at least a part of the NALU because of the
because of the additional packets employed for its transmission. additional packets employed for its transmission.
If a fragmentation unit is lost, the receiver SHOULD discard all If a fragmentation unit is lost, the receiver SHOULD discard all
following fragmentation units in transmission order corresponding following fragmentation units in transmission order corresponding to
to the same fragmented NAL unit. the same fragmented NAL unit.
A receiver in an endpoint or in a MANE MAY aggregate the first n-1 A receiver in an endpoint or in a MANE MAY aggregate the first n-1
fragments of a NAL unit to an (incomplete) NAL unit, even if fragments of a NAL unit to an (incomplete) NAL unit, even if fragment
fragment n of that NAL unit is not received. In this case, the n of that NAL unit is not received. In this case, the
forbidden_zero_bit of the NAL unit MUST be set to one to indicate a forbidden_zero_bit of the NAL unit MUST be set to one to indicate a
syntax violation. syntax violation.
6. Packetization Rules 6. Packetization Rules
The packetization modes are introduced in section 5.2. The The packetization modes are introduced in Section 5.2. The
packetization rules common to more than one of the packetization packetization rules common to more than one of the packetization
modes are specified in section 6.1. The packetization rules for modes are specified in Section 6.1. The packetization rules for the
the single NAL unit mode, the non-interleaved mode, and the single NAL unit mode, the non-interleaved mode, and the interleaved
interleaved mode are specified in sections 6.2, 6.3, and 6.4, mode are specified in Sections 6.2, 6.3, and 6.4, respectively.
respectively.
6.1. Common Packetization Rules 6.1. Common Packetization Rules
All senders MUST enforce the following packetization rules All senders MUST enforce the following packetization rules,
regardless of the packetization mode in use: regardless of the packetization mode in use:
o Coded slice NAL units or coded slice data partition NAL units o Coded slice NAL units or coded slice data partition NAL units
belonging to the same coded picture (and thus sharing the same belonging to the same coded picture (and thus sharing the same RTP
RTP timestamp value) MAY be sent in any order; however, for timestamp value) MAY be sent in any order; however, for delay-
delay-critical systems, they SHOULD be sent in their original critical systems, they SHOULD be sent in their original decoding
decoding order to minimize the delay. Note that the decoding order to minimize the delay. Note that the decoding order is the
order is the order of the NAL units in the bitstream. order of the NAL units in the bitstream.
o Parameter sets are handled in accordance with the rules and o Parameter sets are handled in accordance with the rules and
recommendations given in section 8.4. recommendations given in Section 8.4.
o MANEs MUST NOT duplicate any NAL unit except for sequence or o MANEs MUST NOT duplicate any NAL unit except for sequence or
picture parameter set NAL units, as neither this memo nor the picture parameter set NAL units, as neither this memo nor the
H.264 specification provides means to identify duplicated NAL H.264 specification provides means to identify duplicated NAL
units. Sequence and picture parameter set NAL units MAY be units. Sequence and picture parameter set NAL units MAY be
duplicated to make their correct reception more probable, but duplicated to make their correct reception more probable, but any
any such duplication MUST NOT affect the contents of any active such duplication MUST NOT affect the contents of any active
sequence or picture parameter set. Duplication SHOULD be sequence or picture parameter set. Duplication SHOULD be
performed on the application layer and not by duplicating RTP performed on the application layer and not by duplicating RTP
packets (with identical sequence numbers). packets (with identical sequence numbers).
Senders using the non-interleaved mode and the interleaved mode Senders using the non-interleaved mode and the interleaved mode MUST
MUST enforce the following packetization rule: enforce the following packetization rule:
o MANEs MAY convert single NAL unit packets into one aggregation o In an RTP translator, MANEs MAY convert single NAL unit packets
packet, convert an aggregation packet into several single NAL into one aggregation packet, convert an aggregation packet into
unit packets, or mix both concepts, in an RTP translator. The several single NAL unit packets, or mix both concepts. The RTP
RTP translator SHOULD take into account at least the following translator SHOULD take into account at least the following
parameters: path MTU size, unequal protection mechanisms (e.g., parameters: path MTU size, unequal protection mechanisms (e.g.,
through packet-based FEC according to RFC 2733 [18], especially through packet-based FEC according to RFC 5109 [18], especially
for sequence and picture parameter set NAL units and coded slice for sequence and picture parameter set NAL units and coded slice
data partition A NAL units), bearable latency of the system, and data partition A NAL units), bearable latency of the system, and
buffering capabilities of the receiver. buffering capabilities of the receiver.
Informative note: An RTP translator is required to handle Informative note: An RTP translator is required to handle RTP
RTCP as per RFC 3550. Control Protocol (RTCP) as per RFC 3550.
6.2. Single NAL Unit Mode 6.2. Single NAL Unit Mode
This mode is in use when the value of the OPTIONAL packetization- This mode is in use when the value of the OPTIONAL packetization-mode
mode media type parameter is equal to 0 or the packetization-mode media type parameter is equal to 0 or the packetization-mode is not
is not present. All receivers MUST support this mode. It is present. All receivers MUST support this mode. It is primarily
primarily intended for low-delay applications that are compatible intended for low-delay applications that are compatible with systems
with systems using ITU-T Recommendation H.241 [3] (see section using ITU-T Recommendation H.241 [3] (see Section 12.1). Only single
12.1). Only single NAL unit packets MAY be used in this mode. NAL unit packets MAY be used in this mode. STAPs, MTAPs, and FUs
STAPs, MTAPs, and FUs MUST NOT be used. The transmission order of MUST NOT be used. The transmission order of single NAL unit packets
single NAL unit packets MUST comply with the NAL unit decoding MUST comply with the NAL unit decoding order.
order.
6.3. Non-Interleaved Mode 6.3. Non-Interleaved Mode
This mode is in use when the value of the OPTIONAL packetization- This mode is in use when the value of the OPTIONAL packetization-mode
mode media type parameter is equal to 1. This mode SHOULD be media type parameter is equal to 1. This mode SHOULD be supported.
supported. It is primarily intended for low-delay applications. It is primarily intended for low-delay applications. Only single NAL
Only single NAL unit packets, STAP-As, and FU-As MAY be used in unit packets, STAP-As, and FU-As MAY be used in this mode. STAP-Bs,
this mode. STAP-Bs, MTAPs, and FU-Bs MUST NOT be used. The MTAPs, and FU-Bs MUST NOT be used. The transmission order of NAL
transmission order of NAL units MUST comply with the NAL unit units MUST comply with the NAL unit decoding order.
decoding order.
6.4. Interleaved Mode 6.4. Interleaved Mode
This mode is in use when the value of the OPTIONAL packetization- This mode is in use when the value of the OPTIONAL packetization-mode
mode media type parameter is equal to 2. Some receivers MAY media type parameter is equal to 2. Some receivers MAY support this
support this mode. STAP-Bs, MTAPs, FU-As, and FU-Bs MAY be used. mode. STAP-Bs, MTAPs, FU-As, and FU-Bs MAY be used. STAP-As and
STAP-As and single NAL unit packets MUST NOT be used. The single NAL unit packets MUST NOT be used. The transmission order of
transmission order of packets and NAL units is constrained as packets and NAL units is constrained as specified in Section 5.5.
specified in section 5.5.
7. De-Packetization Process 7. De-Packetization Process
The de-packetization process is implementation dependent. The de-packetization process is implementation dependent. Therefore,
Therefore, the following description should be seen as an example the following description should be seen as an example of a suitable
of a suitable implementation. Other schemes may be used as well as implementation. Other schemes may also be used as long as the output
long as the output for the same input is the same as the process for the same input is the same as the process described below. The
described below. The same output means that the resulting NAL same output means that the resulting NAL units and their order are
units, and their order, are identical. Optimizations relative to identical. Optimizations relative to the described algorithms are
the described algorithms are likely possible. Section 7.1 presents likely possible. Section 7.1 presents the de-packetization process
the de-packetization process for the single NAL unit and non- for the single NAL unit and non-interleaved packetization modes,
interleaved packetization modes, whereas section 7.2 describes the whereas Section 7.2 describes the process for the interleaved mode.
process for the interleaved mode. Section 7.3 includes additional Section 7.3 includes additional de-packetization guidelines for
de-packetization guidelines for intelligent receivers. intelligent receivers.
All normal RTP mechanisms related to buffer management apply. In All normal RTP mechanisms related to buffer management apply. In
particular, duplicated or outdated RTP packets (as indicated by the particular, duplicated or outdated RTP packets (as indicated by the
RTP sequence number and the RTP timestamp) are removed. To RTP sequence number and the RTP timestamp) are removed. To determine
determine the exact time for decoding, factors such as a possible the exact time for decoding, factors such as a possible intentional
intentional delay to allow for proper inter-stream synchronization delay to allow for proper inter-stream synchronization must be
must be factored in. factored in.
7.1. Single NAL Unit and Non-Interleaved Mode 7.1. Single NAL Unit and Non-Interleaved Mode
The receiver includes a receiver buffer to compensate for The receiver includes a receiver buffer to compensate for
transmission delay jitter. The receiver stores incoming packets in transmission delay jitter. The receiver stores incoming packets in
reception order into the receiver buffer. Packets are de- reception order into the receiver buffer. Packets are de-packetized
packetized in RTP sequence number order. If a de-packetized packet in RTP sequence number order. If a de-packetized packet is a single
is a single NAL unit packet, the NAL unit contained in the packet NAL unit packet, the NAL unit contained in the packet is passed
is passed directly to the decoder. If a de-packetized packet is an directly to the decoder. If a de-packetized packet is an STAP-A, the
STAP-A, the NAL units contained in the packet are passed to the NAL units contained in the packet are passed to the decoder in the
decoder in the order in which they are encapsulated in the packet. order in which they are encapsulated in the packet. For all the FU-A
For all the FU-A packets containing fragments of a single NAL unit, packets containing fragments of a single NAL unit, the de-packetized
the de-packetized fragments are concatenated in their sending order fragments are concatenated in their sending order to recover the NAL
to recover the NAL unit, which is then passed to the decoder. unit, which is then passed to the decoder.
Informative note: If the decoder supports Arbitrary Slice Order, Informative note: If the decoder supports arbitrary slice order,
coded slices of a picture can be passed to the decoder in any coded slices of a picture can be passed to the decoder in any
order regardless of their reception and transmission order. order, regardless of their reception and transmission order.
7.2. Interleaved Mode 7.2. Interleaved Mode
The general concept behind these de-packetization rules is to The general concept behind these de-packetization rules is to reorder
reorder NAL units from transmission order to the NAL unit decoding NAL units from transmission order to the NAL unit decoding order.
order.
The receiver includes a receiver buffer, which is used to The receiver includes a receiver buffer, which is used to compensate
compensate for transmission delay jitter and to reorder NAL units for transmission delay jitter and to reorder NAL units from
from transmission order to the NAL unit decoding order. In this transmission order to the NAL unit decoding order. In this section,
section, the receiver operation is described under the assumption the receiver operation is described under the assumption that there
that there is no transmission delay jitter. To make a difference is no transmission delay jitter. To differentiate the receiver
from a practical receiver buffer that is also used for compensation buffer from a practical receiver buffer that is also used for
of transmission delay jitter, the receiver buffer is here after compensation of transmission delay jitter, the receiver buffer is
called the de-interleaving buffer in this section. Receivers hereafter called the de-interleaving buffer in this section.
SHOULD also prepare for transmission delay jitter; i.e., either Receivers SHOULD also prepare for transmission delay jitter, i.e.,
reserve separate buffers for transmission delay jitter buffering either reserve separate buffers for transmission delay jitter
and de-interleaving buffering or use a receiver buffer for both buffering and de-interleaving buffering or use a receiver buffer for
transmission delay jitter and de-interleaving. Moreover, receivers both transmission delay jitter and de-interleaving. Moreover,
SHOULD take transmission delay jitter into account in the buffering receivers SHOULD take transmission delay jitter into account in the
operation; e.g., by additional initial buffering before starting of buffering operation, e.g., by additional initial buffering before
decoding and playback. starting of decoding and playback.
This section is organized as follows: subsection 7.2.1 presents how This section is organized as follows: Subsection 7.2.1 presents how
to calculate the size of the de-interleaving buffer. Subsection to calculate the size of the de-interleaving buffer. Subsection
7.2.2 specifies the receiver process on how to organize received 7.2.2 specifies the receiver process on how to organize received NAL
NAL units to the NAL unit decoding order. units to the NAL unit decoding order.
7.2.1. Size of the De-interleaving Buffer 7.2.1. Size of the De-Interleaving Buffer
In either Offer/Answer or declarative SDP usage, the sprop-deint- In either Offer/Answer or declarative Session Description Protocol
buf-req media type parameter signals the requirement for the de- (SDP) usage, the sprop-deint-buf-req media type parameter signals the
interleaving buffer size. It is therefore RECOMMENDED to set the requirement for the de-interleaving buffer size. Therefore, it is
de-interleaving buffer size, in terms of number of bytes, equal to RECOMMENDED to set the de-interleaving buffer size, in terms of
or greater than the value of sprop-deint-buf-req media type number of bytes, equal to or greater than the value of the sprop-
parameter. deint-buf-req media type parameter.
When the SDP Offer/Answer model or any other capability exchange When the SDP Offer/Answer model or any other capability exchange
procedure is used in session setup, the properties of the received procedure is used in session setup, the properties of the received
stream SHOULD be such that the receiver capabilities are not stream SHOULD be such that the receiver capabilities are not
exceeded. In the SDP Offer/Answer model, the receiver can indicate exceeded. In the SDP Offer/Answer model, the receiver can indicate
its capabilities to allocate a de-interleaving buffer with the its capabilities to allocate a de-interleaving buffer with the deint-
deint-buf-cap media type parameter. See section 8.1 for further buf-cap media type parameter. See Section 8.1 for further
information on deint-buf-cap and sprop-deint-buf-req media type information on the deint-buf-cap and sprop-deint-buf-req media type
parameters and section 8.2.2 for further information on their use parameters and Section 8.2.2 for further information on their use in
in the SDP Offer/Answer model. the SDP Offer/Answer model.
7.2.2. De-interleaving Process 7.2.2. De-Interleaving Process
There are two buffering states in the receiver: initial buffering There are two buffering states in the receiver: initial buffering and
and buffering while playing. Initial buffering occurs when the RTP buffering while playing. Initial buffering occurs when the RTP
session is initialized. After initial buffering, decoding and session is initialized. After initial buffering, decoding and
playback are started, and the buffering-while-playing mode is used. playback are started, and the buffering-while-playing mode is used.
Regardless of the buffering state, the receiver stores incoming NAL Regardless of the buffering state, the receiver stores incoming NAL
units, in reception order, in the de-interleaving buffer as follows. units, in reception order, in the de-interleaving buffer as follows.
NAL units of aggregation packets are stored in the de-interleaving NAL units of aggregation packets are stored in the de-interleaving
buffer individually. The value of DON is calculated and stored for buffer individually. The value of DON is calculated and stored for
each NAL unit. each NAL unit.
The receiver operation is described below with the help of the The receiver operation is described below with the help of the
following functions and constants: following functions and constants:
o Function AbsDON is specified in section 8.1. o Function AbsDON is specified in Section 8.1.
o Function don_diff is specified in section 5.5. o Function don_diff is specified in Section 5.5.
o Constant N is the value of the OPTIONAL sprop-interleaving-depth o Constant N is the value of the OPTIONAL sprop-interleaving-depth
media type parameter (see section 8.1) incremented by 1. media type parameter (see Section 8.1) incremented by 1.
Initial buffering lasts until one of the following conditions is Initial buffering lasts until one of the following conditions is
fulfilled: fulfilled:
o There are N or more VCL NAL units in the de-interleaving buffer. o There are N or more VCL NAL units in the de-interleaving buffer.
o If sprop-max-don-diff is present, don_diff(m,n) is greater than o If sprop-max-don-diff is present, don_diff(m,n) is greater than
the value of sprop-max-don-diff, in which n corresponds to the the value of sprop-max-don-diff, in which n corresponds to the NAL
NAL unit having the greatest value of AbsDON among the received unit having the greatest value of AbsDON among the received NAL
NAL units and m corresponds to the NAL unit having the smallest units and m corresponds to the NAL unit having the smallest value
value of AbsDON among the received NAL units. of AbsDON among the received NAL units.
o Initial buffering has lasted for the duration equal to or o Initial buffering has lasted for the duration equal to or greater
greater than the value of the OPTIONAL sprop-init-buf-time media than the value of the OPTIONAL sprop-init-buf-time media type
type parameter. parameter.
The NAL units to be removed from the de-interleaving buffer are The NAL units to be removed from the de-interleaving buffer are
determined as follows: determined as follows:
o If the de-interleaving buffer contains at least N VCL NAL units, o If the de-interleaving buffer contains at least N VCL NAL units,
NAL units are removed from the de-interleaving buffer and passed NAL units are removed from the de-interleaving buffer and passed
to the decoder in the order specified below until the buffer to the decoder in the order specified below until the buffer
contains N-1 VCL NAL units. contains N-1 VCL NAL units.
o If sprop-max-don-diff is present, all NAL units m for which o If sprop-max-don-diff is present, all NAL units m for which
don_diff(m,n) is greater than sprop-max-don-diff are removed don_diff(m,n) is greater than sprop-max-don-diff are removed from
from the de-interleaving buffer and passed to the decoder in the the de-interleaving buffer and passed to the decoder in the order
order specified below. Herein, n corresponds to the NAL unit specified below. Herein, n corresponds to the NAL unit having the
having the greatest value of AbsDON among the NAL units in the greatest value of AbsDON among the NAL units in the de-
de-interleaving buffer. interleaving buffer.
The order in which NAL units are passed to the decoder is specified The order in which NAL units are passed to the decoder is specified
as follows: as follows:
o Let PDON be a variable that is initialized to 0 at the beginning o Let PDON be a variable that is initialized to 0 at the beginning
of the RTP session. of the RTP session.
o For each NAL unit associated with a value of DON, a DON distance o For each NAL unit associated with a value of DON, a DON distance
is calculated as follows. If the value of DON of the NAL unit is calculated as follows. If the value of DON of the NAL unit is
is larger than the value of PDON, the DON distance is equal to larger than the value of PDON, the DON distance is equal to DON -
DON - PDON. Otherwise, the DON distance is equal to 65535 - PDON. Otherwise, the DON distance is equal to 65535 - PDON + DON
PDON + DON + 1. + 1.
o NAL units are delivered to the decoder in ascending order of DON o NAL units are delivered to the decoder in ascending order of DON
distance. If several NAL units share the same value of DON distance. If several NAL units share the same value of DON
distance, they can be passed to the decoder in any order. distance, they can be passed to the decoder in any order.
o When a desired number of NAL units have been passed to the o When a desired number of NAL units have been passed to the
decoder, the value of PDON is set to the value of DON for the decoder, the value of PDON is set to the value of DON for the last
last NAL unit passed to the decoder. NAL unit passed to the decoder.
7.3. Additional De-Packetization Guidelines 7.3. Additional De-Packetization Guidelines
The following additional de-packetization rules may be used to The following additional de-packetization rules may be used to
implement an operational H.264 de-packetizer: implement an operational H.264 de-packetizer:
o Intelligent RTP receivers (e.g., in gateways) may identify lost o Intelligent RTP receivers (e.g., in gateways) may identify lost
coded slice data partitions A (DPAs). If a lost DPA is detected, coded slice data partitions A (DPAs). If a lost DPA is detected,
after taking into account possible retransmission and FEC, a after taking into account possible retransmission and FEC, a
gateway may decide not to send the corresponding coded slice gateway may decide not to send the corresponding coded slice data
data partitions B and C, as their information is meaningless for partitions B and C, as their information is meaningless for H.264
H.264 decoders. In this way a MANE can reduce network load by decoders. In this way, a MANE can reduce network load by
discarding useless packets without parsing a complex bitstream. discarding useless packets without parsing a complex bitstream.
o Intelligent RTP receivers (e.g., in gateways) may identify lost o Intelligent RTP receivers (e.g., in gateways) may identify lost
FUs. If a lost FU is found, a gateway may decide not to send FUs. If a lost FU is found, a gateway may decide not to send the
the following FUs of the same fragmented NAL unit, as their following FUs of the same fragmented NAL unit, as their
information is meaningless for H.264 decoders. In this way a information is meaningless for H.264 decoders. In this way, a
MANE can reduce network load by discarding useless packets MANE can reduce network load by discarding useless packets without
without parsing a complex bitstream. parsing a complex bitstream.
o Intelligent receivers having to discard packets or NALUs should o Intelligent receivers having to discard packets or NALUs should
first discard all packets/NALUs in which the value of the NRI first discard all packets/NALUs in which the value of the NRI
field of the NAL unit type octet is equal to 0. This will field of the NAL unit type octet is equal to 0. This will
minimize the impact on user experience and keep the reference minimize the impact on user experience and keep the reference
pictures intact. If more packets have to be discarded, then pictures intact. If more packets have to be discarded, then
packets with a numerically lower NRI value should be discarded packets with a numerically lower NRI value should be discarded
before packets with a numerically higher NRI value. However, before packets with a numerically higher NRI value. However,
discarding any packets with an NRI bigger than 0 very likely discarding any packets with an NRI bigger than 0 very likely leads
leads to decoder drift and SHOULD be avoided. to decoder drift and SHOULD be avoided.
8. Payload Format Parameters 8. Payload Format Parameters
This section specifies the parameters that MAY be used to select This section specifies the parameters that MAY be used to select
optional features of the payload format and certain features of the optional features of the payload format and certain features of the
bitstream. The parameters are specified here as part of the media bitstream. The parameters are specified here as part of the media
subtype registration for the ITU-T H.264 | ISO/IEC 14496-10 codec. subtype registration for the ITU-T H.264 | ISO/IEC 14496-10 codec. A
A mapping of the parameters into the Session Description Protocol mapping of the parameters into the Session Description Protocol (SDP)
(SDP) [6] is also provided for applications that use SDP. [6] is also provided for applications that use SDP. Equivalent
Equivalent parameters could be defined elsewhere for use with parameters could be defined elsewhere for use with control protocols
control protocols that do not use SDP. that do not use SDP.
Some parameters provide a receiver with the properties of the Some parameters provide a receiver with the properties of the stream
stream that will be sent. The names of all these parameters start that will be sent. The names of all these parameters start with
with "sprop" for stream properties. Some of these "sprop" "sprop" for stream properties. Some of these "sprop" parameters are
parameters are limited by other payload or codec configuration limited by other payload or codec configuration parameters. For
parameters. For example, the sprop-parameter-sets parameter is example, the sprop-parameter-sets parameter is constrained by the
constrained by the profile-level-id parameter. profile-level-id parameter.
8.1. Media Type Registration 8.1. Media Type Registration
The media subtype for the ITU-T H.264 | ISO/IEC 14496-10 codec is The media subtype for the ITU-T H.264 | ISO/IEC 14496-10 codec has
allocated from the IETF tree. been allocated from the IETF tree.
Media Type name: video Media Type name: video
Media subtype name: H264 Media subtype name: H264
Required parameters: none Required parameters: none
OPTIONAL parameters: OPTIONAL parameters:
profile-level-id: profile-level-id:
A base16 [7] (hexadecimal) representation of the following A base16 [7] (hexadecimal) representation of the following
three bytes in the sequence parameter set NAL unit specified three bytes in the sequence parameter set NAL unit is specified
in [1]: 1) profile_idc, 2) a byte herein referred to as in [1]: 1) profile_idc, 2) a byte herein referred to as
profile-iop, composed of the values of constraint_set0_flag, profile-iop, composed of the values of constraint_set0_flag,
constraint_set1_flag,constraint_set2_flag, constraint_set1_flag, constraint_set2_flag,
constraint_set3_flag, and reserved_zero_4bits in bit- constraint_set3_flag, constraint_set4_flag,
significance order, starting from the most significant bit, constraint_set5_flag, and reserved_zero_2bits in bit-
and 3) level_idc. Note that reserved_zero_4bits is required significance order, starting from the most-significant bit, and
to be equal to 0 in [1], but other values for it may be 3) level_idc. Note that reserved_zero_2bits is required to be
specified in the future by ITU-T or ISO/IEC. equal to 0 in [1], but other values for it may be specified in
the future by ITU-T or ISO/IEC.
The profile-level-id parameter indicates the default sub- The profile-level-id parameter indicates the default sub-
profile, i.e. the subset of coding tools that may have been profile (i.e., the subset of coding tools that may have been
used to generate the stream or that the receiver supports, used to generate the stream or that the receiver supports) and
and the default level of the stream or the receiver supports. the default level of the stream or the receiver supports.
The default sub-profile is indicated collectively by the The default sub-profile is indicated collectively by the
profile_idc byte and some fields in the profile-iop byte. profile_idc byte and some fields in the profile-iop byte.
Depending on the values of the fields in the profile-iop byte, Depending on the values of the fields in the profile-iop byte,
the default sub-profile may be the set of coding tools the default sub-profile may be the set of coding tools
supported by one profile, or a common subset of coding tools supported by one profile, or a common subset of coding tools of
of multiple profiles, as specified in subsection 7.4.2.1.1 of multiple profiles, as specified in Section 7.4.2.1.1 of [1].
[1]. The default level is indicated by the level_idc byte, The default level is indicated by the level_idc byte, and, when
and, when profile_idc is equal to 66, 77 or 88 (the Baseline, profile_idc is equal to 66, 77, or 88 (the Baseline, Main, or
Main, or Extended profile) and level_idc is equal to 11, Extended profile) and level_idc is equal to 11, additionally by
additionally by bit 4 (constraint_set3_flag) of the profile- bit 4 (constraint_set3_flag) of the profile-iop byte. When
iop byte. When profile_idc is equal to 66, 77 or 88 (the profile_idc is equal to 66, 77, or 88 (the Baseline, Main, or
Baseline, Main, or Extended profile) and level_idc is equal Extended profile), level_idc is equal to 11, and bit 4
to 11, and bit 4 (constraint_set3_flag) of the profile-iop (constraint_set3_flag) of the profile-iop byte is equal to 1,
byte is equal to 1, the default level is level 1b. the default level is Level 1b.
Table 5 lists all profiles defined in Annex A of [1] and, for Table 5 lists all profiles defined in Annex A of [1] and, for
each of the profiles, the possible combinations of each of the profiles, the possible combinations of profile_idc
profile_idc and profile-iop that represent the same sub- and profile-iop that represent the same sub-profile.
profile.
Table 5. Combinations of profile_idc and profile-iop Table 5. Combinations of profile_idc and profile-iop
representing the same sub-profile corresponding to the representing the same sub-profile corresponding to the full
full set of coding tools supported by one profile. In set of coding tools supported by one profile. In the
the following, x may be either 0 or 1, while the profile following, x may be either 0 or 1, while the profile names
names are indicated as follows. CB: Constrained Baseline are indicated as follows. CB: Constrained Baseline profile,
profile, B: Baseline profile, M: Main profile, E: B: Baseline profile, M: Main profile, E: Extended profile,
Extended profile, H: High profile, H10: High 10 profile, H: High profile, H10: High 10 profile, H42: High 4:2:2
H42: High 4:2:2 profile, H44: High 4:4:4 Predictive profile, H44: High 4:4:4 Predictive profile, H10I: High 10
profile, H10I: High 10 Intra profile, H42I: High 4:2:2 Intra profile, H42I: High 4:2:2 Intra profile, H44I: High
Intra profile, H44I: High 4:4:4 Intra profile, and C44I: 4:4:4 Intra profile, and C44I: CAVLC 4:4:4 Intra profile.
CAVLC 4:4:4 Intra profile.
Profile profile_idc profile-iop Profile profile_idc profile-iop
(hexadecimal) (binary) (hexadecimal) (binary)
CB 42 (B) x1xx0000 CB 42 (B) x1xx0000
same as: 4D (M) 1xxx0000 same as: 4D (M) 1xxx0000
same as: 58 (E) 11xx0000 same as: 58 (E) 11xx0000
same as: 64 (H), 6E (H10), 1xx00000 B 42 (B) x0xx0000
7A (H42), or F4 (H44) same as: 58 (E) 10xx0000
B 42 (B) x0xx0000 M 4D (M) 0x0x0000
same as: 58 (E) 10xx0000 E 58 00xx0000
M 4D (M) 0x0x0000 H 64 00000000
same as: 64 (H), 6E (H10), 01000000 H10 6E 00000000
7A (H42), or F4 (H44) H42 7A 00000000
E 58 00xx0000 H44 F4 00000000
H 64 00000000 H10I 6E 00010000
H10 6E 00000000 H42I 7A 00010000
H42 7A 00000000 H44I F4 00010000
H44 F4 00000000 C44I 2C 00010000
H10I 64 00010000
H42I 7A 00010000
H44I F4 00010000
C44I 2C 00010000
For example, in the table above, profile_idc equal to 58 For example, in the table above, profile_idc equal to 58
(Extended) with profile-iop equal to 11xx0000 indicates the (Extended) with profile-iop equal to 11xx0000 indicates the
same sub-profile corresponding to profile_idc equal to 42 same sub-profile corresponding to profile_idc equal to 42
(Baseline) with profile-iop equal to x1xx0000. Note that (Baseline) with profile-iop equal to x1xx0000. Note that other
other combinations of profile_idc and profile-iop (not listed combinations of profile_idc and profile-iop (not listed in
in Table 5) may represent a sub-profile equivalent to the Table 5) may represent a sub-profile equivalent to the common
common subset of coding tools for more than one profile. subset of coding tools for more than one profile. Note also
Note also that a decoder conforming to a certain profile may that a decoder conforming to a certain profile may be able to
be able to decode bitstreams conforming to other profiles. decode bitstreams conforming to other profiles.
For example, a decoder conforming to the High 4:4:4 profile
at certain level must be able to decode bitstreams conforming
to the Constrained Baseline, Main, High, High 10 or High
4:2:2 profile at the same or a lower level.
If the profile-level-id parameter is used to indicate If the profile-level-id parameter is used to indicate
properties of a NAL unit stream, it indicates that, to decode properties of a NAL unit stream, it indicates that, to decode
the stream, the minimum subset of coding tools a decoder has the stream, the minimum subset of coding tools a decoder has to
to support is the default sub-profile, and the lowest level support is the default sub-profile, and the lowest level the
the decoder has to support is the default level. decoder has to support is the default level.
If the profile-level-id parameter is used for capability If the profile-level-id parameter is used for capability
exchange or session setup procedure, it indicates the subset exchange or session setup, it indicates the subset of coding
of coding tools, which is equal to the default sub-profile, tools, which is equal to the default sub-profile, that the
that the codec supports for both receiving and sending. If codec supports for both receiving and sending. If max-recv-
max-recv-level is not present, the default level from level is not present, the default level from profile-level-id
profile-level-id indicates the highest level the codec wishes indicates the highest level the codec wishes to support. If
to support. If max-recv-level is present it indicates the max-recv-level is present, it indicates the highest level the
highest level the codec supports for receiving. For either codec supports for receiving. For either receiving or sending,
receiving or sending, all levels that are lower than the all levels that are lower than the highest level supported MUST
highest level supported MUST also be supported. also be supported.
Informative note: Capability exchange and session setup Informative note: Capability exchange and session setup
procedures should provide means to list the capabilities procedures should provide means to list the capabilities for
for each supported sub-profile separately. For example, each supported sub-profile separately. For example, the
the one-of-N codec selection procedure of the SDP one-of-N codec selection procedure of the SDP Offer/Answer
Offer/Answer model can be used (section 10.2 of [8]). model can be used (Section 10.2 of [8]). The one-of-N codec
The one-of-N codec selection procedure may also be used selection procedure may also be used to provide different
to provide different combinations of profile_idc and combinations of profile_idc and profile-iop that represent
profile-iop that represent the same sub-profile. When the same sub-profile. When there are many different
there are many different combinations of profile_idc and combinations of profile_idc and profile-iop that represent
profile-iop that represent the same sub-profile, using the same sub-profile, using the one-of-N codec selection
the one-of-N codec selection procedure may result into a procedure may result in a fairly large SDP message.
fairly large SDP message. Therefore, a receiver should Therefore, a receiver should understand the different
understand the different equivalent combinations of equivalent combinations of profile_idc and profile-iop that
profile_idc and profile-iop that represent the same sub- represent the same sub-profile and be ready to accept an
profile, and be ready to accept an offer using any of the offer using any of the equivalent combinations.
equivalent combinations.
If no profile-level-id is present, the Baseline Profile If no profile-level-id is present, the Baseline profile,
without additional constraints at Level 1 MUST be inferred. without additional constraints at Level 1, MUST be inferred.
max-recv-level: max-recv-level:
This parameter MAY be used to indicate the highest level a This parameter MAY be used to indicate the highest level a
receiver supports when the highest level is higher than the receiver supports when the highest level is higher than the
default level (the level indicated by profile-level-id). The default level (the level indicated by profile-level-id). The
value of max-recv-level is a base16 (hexadecimal) value of max-recv-level is a base16 (hexadecimal)
representation of the two bytes after the syntax element representation of the two bytes after the syntax element
profile_idc in the sequence parameter set NAL unit specified profile_idc in the sequence parameter set NAL unit specified in
in [1]: profile-iop (as defined above) and level_idc. If [1]: profile-iop (as defined above) and level_idc. If the
(the level_idc byte of max-recv-level is equal to 11 and bit level_idc byte of max-recv-level is equal to 11 and bit 4 of
4 of the profile-iop byte of max-recv-level is equal to 1) or the profile-iop byte of max-recv-level is equal to 1 or if the
(the level_idc byte of max-recv-level is equal to 9 and bit 4 level_idc byte of max-recv-level is equal to 9 and bit 4 of the
of the profile-iop byte of max-recv-level is equal to 0), the profile-iop byte of max-recv-level is equal to 0, the highest
highest level the receiver supports is level 1b. Otherwise, level the receiver supports is Level 1b. Otherwise, the
the highest level the receiver supports is equal to the highest level the receiver supports is equal to the level_idc
level_idc byte of max-recv-level divided by 10. byte of max-recv-level divided by 10.
max-recv-level MUST NOT be present if the highest level the max-recv-level MUST NOT be present if the highest level the
receiver supports is not higher than the default level. receiver supports is not higher than the default level.
max-mbps, max-smbps, max-fs, max-cpb, max-dpb, and max-br: max-mbps, max-smbps, max-fs, max-cpb, max-dpb, and max-br:
These parameters MAY be used to signal the capabilities of a These parameters MAY be used to signal the capabilities of a
receiver implementation. These parameters MUST NOT be used receiver implementation. These parameters MUST NOT be used for
for any other purpose. The highest level conveyed in the any other purpose. The highest level conveyed in the value of
value of the profile-level-id parameter or the max-recv-level the profile-level-id parameter or the max-recv-level parameter
parameter MUST be such that the receiver is fully capable of MUST be such that the receiver is fully capable of supporting.
supporting. max-mbps, max-smbps, max-fs, max-cpb, max-dpb, max-mbps, max-smbps, max-fs, max-cpb, max-dpb, and max-br MAY
and max-br MAY be used to indicate capabilities of the be used to indicate capabilities of the receiver that extend
receiver that extend the required capabilities of the the required capabilities of the signaled highest level, as
signaled highest level, as specified below. specified below.
When more than one parameter from the set (max-mbps, max- When more than one parameter from the set (max-mbps, max-smbps,
smbps , max-fs, max-cpb, max-dpb, max-br) is present, the max-fs, max-cpb, max-dpb, max-br) is present, the receiver MUST
receiver MUST support all signaled capabilities support all signaled capabilities simultaneously. For example,
simultaneously. For example, if both max-mbps and max-br are if both max-mbps and max-br are present, the signaled highest
present, the signaled highest level with the extension of level with the extension of both the frame rate and bitrate is
both the frame rate and bit rate is supported. That is, the supported. That is, the receiver is able to decode NAL unit
receiver is able to decode NAL unit streams in which the streams in which the macroblock processing rate is up to max-
macroblock processing rate is up to max-mbps (inclusive), the mbps (inclusive), the bitrate is up to max-br (inclusive), the
bit rate is up to max-br (inclusive), the coded picture coded picture buffer size is derived as specified in the
buffer size is derived as specified in the semantics of the semantics of the max-br parameter below, and the other
max-br parameter below, and other properties comply with the properties comply with the highest level specified in the value
highest level specified in the value of the profile-level-id of the profile-level-id parameter or the max-recv-level
parameter or the max-recv-level parameter. parameter.
If a receiver can support all the properties of level A, the If a receiver can support all the properties of Level A, the
highest level specified in the value of the profile-level-id highest level specified in the value of the profile-level-id
parameter or the max-recv-level parameter MUST be level A parameter or the max-recv-level parameter MUST be Level A
(i.e. MUST NOT be lower than level A). In other words, a (i.e., MUST NOT be lower than Level A). In other words, a
receiver MUST NOT signal values of max-mbps, max-fs, max-cpb, receiver MUST NOT signal values of max-mbps, max-fs, max-cpb,
max-dpb, and max-br that taken together meet the requirements max-dpb, and max-br that taken together meet the requirements
of a higher level compared to the highest level specified in of a higher level compared to the highest level specified in
the value of the profile-level-id parameter or the max-recv- the value of the profile-level-id parameter or the max-recv-
level parameter. level parameter.
Informative note: When the OPTIONAL media type parameters Informative note: When the OPTIONAL media type parameters
are used to signal the properties of a NAL unit stream, are used to signal the properties of a NAL unit stream, max-
max-mbps, max-smbps, max-fs, max-cpb, max-dpb, and max-br mbps, max-smbps, max-fs, max-cpb, max-dpb, and max-br are
are not present, and the value of profile-level-id must not present, and the value of profile-level-id must always
always be such that the NAL unit stream complies fully be such that the NAL unit stream complies fully with the
with the specified profile and level. specified profile and level.
max-mbps: The value of max-mbps is an integer indicating the max-mbps: The value of max-mbps is an integer indicating the
maximum macroblock processing rate in units of macroblocks maximum macroblock processing rate in units of macroblocks per
per second. The max-mbps parameter signals that the receiver second. The max-mbps parameter signals that the receiver is
is capable of decoding video at a higher rate than is capable of decoding video at a higher rate than is required by
required by the signaled highest level conveyed in the value the signaled highest level conveyed in the value of the
of the profile-level-id parameter or the max-recv-level profile-level-id parameter or the max-recv-level parameter.
parameter. When max-mbps is signaled, the receiver MUST be
able to decode NAL unit streams that conform to the signaled
highest level, with the exception that the MaxMBPS value in
Table A-1 of [1] for the signaled highest level is replaced
with the value of max-mbps. The value of max-mbps MUST be
greater than or equal to the value of MaxMBPS given in Table
A-1 of [1] for the highest level. Senders MAY use this
knowledge to send pictures of a given size at a higher
picture rate than is indicated in the signaled highest level.
max-smbps: The value of max-smbps is an integer indicating the When max-mbps is signaled, the receiver MUST be able to decode
maximum static macroblock processing rate in units of static NAL unit streams that conform to the signaled highest level,
macroblocks per second, under the hypothetical assumption with the exception that the MaxMBPS value in Table A-1 of [1]
that all macroblocks are static macroblocks. When max-smbps for the signaled highest level is replaced with the value of
is signaled the MaxMBPS value in Table A-1 of [1] should be max-mbps. The value of max-mbps MUST be greater than or equal
replaced with the result of the following computation: to the value of MaxMBPS given in Table A-1 of [1] for the
highest level. Senders MAY use this knowledge to send pictures
of a given size at a higher picture rate than is indicated in
the signaled highest level.
o If the parameter max-mbps is signaled, set a variable max-smbps: The value of max-smbps is an integer indicating the
maximum static macroblock processing rate in units of static
macroblocks per second, under the hypothetical assumption that
all macroblocks are static macroblocks. When max-smbps is
signaled, the MaxMBPS value in Table A-1 of [1] should be
replaced with the result of the following computation:
o If the parameter max-mbps is signaled, set a variable
MaxMacroblocksPerSecond to the value of max-mbps. MaxMacroblocksPerSecond to the value of max-mbps.
Otherwise, set MaxMacroblocksPerSecond equal to the value Otherwise, set MaxMacroblocksPerSecond equal to the value of
of MaxMBPS in Table A-1 [1] for the signaled highest level MaxMBPS in Table A-1 [1] for the signaled highest level
conveyed in the value of the profile-level-id parameter or conveyed in the value of the profile-level-id parameter or
the max-recv-level parameter. the max-recv-level parameter.
o Set a variable P_non-static to the proportion of non- o Set a variable P_non-static to the proportion of non-static
static macroblocks in picture n. macroblocks in picture n.
o Set a variable P_static to the proportion of static o Set a variable P_static to the proportion of static
macroblocks in picture n. macroblocks in picture n.
o The value of MaxMBPS in Table A-1 of [1] should be o The value of MaxMBPS in Table A-1 of [1] should be
considered by the encoder to be equal to: considered by the encoder to be equal to:
MaxMacroblocksPerSecond * max-smbps / (P_non-static * MaxMacroblocksPerSecond * max-smbps / (P_non-static *
max-smbps + P_static * MaxMacroblocksPerSecond) max-smbps + P_static * MaxMacroblocksPerSecond)
The encoder should recompute this value for each picture. The
value of max-smbps MUST be greater than or equal to the value
of MaxMBPS given explicitly as the value of the max-mbps
parameter or implicitly in Table A-1 of [1] for the signaled
highest level. Senders MAY use this knowledge to send
pictures of a given size at a higher picture rate than is
indicated in the signaled highest level.
max-fs: The value of max-fs is an integer indicating the maximum The encoder should recompute this value for each picture. The
frame size in units of macroblocks. The max-fs parameter value of max-smbps MUST be greater than or equal to the value
signals that the receiver is capable of decoding larger of MaxMBPS given explicitly as the value of the max-mbps
picture sizes than are required by the signaled highest level parameter or implicitly in Table A-1 of [1] for the signaled
conveyed in the value of the profile-level-id parameter or highest level. Senders MAY use this knowledge to send pictures
the max-recv-level parameter. When max-fs is signaled, the of a given size at a higher picture rate than is indicated in
receiver MUST be able to decode NAL unit streams that conform the signaled highest level.
to the signaled highest level, with the exception that the
MaxFS value in Table A-1 of [1] for the signaled highest
level is replaced with the value of max-fs. The value of
max-fs MUST be greater than or equal to the value of MaxFS
given in Table A-1 of [1] for the highest level. Senders MAY
use this knowledge to send larger pictures at a
proportionally lower frame rate than is indicated in the
signaled highest level.
max-cpb: The value of max-cpb is an integer indicating the max-fs: The value of max-fs is an integer indicating the maximum
maximum coded picture buffer size in units of 1000 bits for frame size in units of macroblocks. The max-fs parameter
the VCL HRD parameters (see A.3.1 item i of [1]) and in units signals that the receiver is capable of decoding larger picture
of 1200 bits for the NAL HRD parameters (see A.3.1 item j of sizes than are required by the signaled highest level conveyed
[1]). The max-cpb parameter signals that the receiver has in the value of the profile-level-id parameter or the max-recv-
more memory than the minimum amount of coded picture buffer level parameter. When max-fs is signaled, the receiver MUST be
memory required by the signaled highest level conveyed in the able to decode NAL unit streams that conform to the signaled
value of the profile-level-id parameter or the max-recv-level highest level, with the exception that the MaxFS value in Table
parameter. When max-cpb is signaled, the receiver MUST be A-1 of [1] for the signaled highest level is replaced with the
able to decode NAL unit streams that conform to the signaled value of max-fs. The value of max-fs MUST be greater than or
highest level, with the exception that the MaxCPB value in equal to the value of MaxFS given in Table A-1 of [1] for the
Table A-1 of [1] for the signaled highest level is replaced highest level. Senders MAY use this knowledge to send larger
with the value of max-cpb. The value of max-cpb MUST be pictures at a proportionally lower frame rate than is indicated
greater than or equal to the value of MaxCPB given in Table in the signaled highest level.
A-1 of [1] for the highest level. Senders MAY use this
knowledge to construct coded video streams with greater
variation of bit rate than can be achieved with the MaxCPB
value in Table A-1 of [1].
Informative note: The coded picture buffer is used in the max-cpb: The value of max-cpb is an integer indicating the maximum
hypothetical reference decoder (Annex C) of H.264. The coded picture buffer size in units of 1000 bits for the VCL HRD
use of the hypothetical reference decoder is recommended parameters and in units of 1200 bits for the NAL HRD
in H.264 encoders to verify that the produced bitstream parameters. Note that this parameter does not use units of
conforms to the standard and to control the output cpbBrVclFactor and cpbBrNALFactor (see Table A-1 of [1]). The
bitrate. Thus, the coded picture buffer is conceptually max-cpb parameter signals that the receiver has more memory
independent of any other potential buffers in the than the minimum amount of coded picture buffer memory required
receiver, including de-interleaving and de-jitter buffers. by the signaled highest level conveyed in the value of the
The coded picture buffer need not be implemented in profile-level-id parameter or the max-recv-level parameter.
decoders as specified in Annex C of H.264, but rather When max-cpb is signaled, the receiver MUST be able to decode
standard-compliant decoders can have any buffering NAL unit streams that conform to the signaled highest level,
arrangements provided that they can decode standard- with the exception that the MaxCPB value in Table A-1 of [1]
compliant bitstreams. Thus, in practice, the input for the signaled highest level is replaced with the value of
buffer for video decoder can be integrated with de- max-cpb (after taking cpbBrVclFactor and cpbBrNALFactor into
interleaving and de-jitter buffers of the receiver. consideration when needed). The value of max-cpb (after taking
cpbBrVclFactor and cpbBrNALFactor into consideration when
needed) MUST be greater than or equal to the value of MaxCPB
given in Table A-1 of [1] for the highest level. Senders MAY
use this knowledge to construct coded video streams with
greater variation of bitrate than can be achieved with the
MaxCPB value in Table A-1 of [1].
max-dpb: The value of max-dpb is an integer indicating the Informative note: The coded picture buffer is used in the
maximum decoded picture buffer size in units of 1024 bytes. hypothetical reference decoder (Annex C of H.264). The use
The max-dpb parameter signals that the receiver has more of the hypothetical reference decoder is recommended in
memory than the minimum amount of decoded picture buffer H.264 encoders to verify that the produced bitstream
memory required by the signaled highest level conveyed in the conforms to the standard and to control the output bitrate.
value of the profile-level-id parameter or the max-recv-level Thus, the coded picture buffer is conceptually independent
parameter. When max-dpb is signaled, the receiver MUST be of any other potential buffers in the receiver, including
able to decode NAL unit streams that conform to the signaled de-interleaving and de-jitter buffers. The coded picture
highest level, with the exception that the MaxDPB value in buffer need not be implemented in decoders as specified in
Table A-1 of [1] for the signaled highest level is replaced Annex C of H.264, but rather standard-compliant decoders can
with the value of max-dpb. Consequently, a receiver that have any buffering arrangements provided that they can
signals max-dpb MUST be capable of storing the following decode standard-compliant bitstreams. Thus, in practice,
number of decoded frames, complementary field pairs, and non- the input buffer for a video decoder can be integrated with
paired fields in its decoded picture buffer: de-interleaving and de-jitter buffers of the receiver.
Min(1024 * max-dpb / ( PicWidthInMbs * FrameHeightInMbs * max-dpb: The value of max-dpb is an integer indicating the maximum
256 * ChromaFormatFactor ), 16) decoded picture buffer size in units of 8/3 macroblocks. The
max-dpb parameter signals that the receiver has more memory
than the minimum amount of decoded picture buffer memory
required by the signaled highest level conveyed in the value of
the profile-level-id parameter or the max-recv-level parameter.
When max-dpb is signaled, the receiver MUST be able to decode
NAL unit streams that conform to the signaled highest level,
with the exception that the MaxDpbMbs value in Table A-1 of [1]
for the signaled highest level is replaced with the value of
max-dpb * 3 / 8. Consequently, a receiver that signals max-dpb
MUST be capable of storing the following number of decoded
frames, complementary field pairs, and non-paired fields in its
decoded picture buffer:
PicWidthInMbs, FrameHeightInMbs, and ChromaFormatFactor are Min(max-dpb * 3 / 8 / ( PicWidthInMbs * FrameHeightInMbs),
defined in [1]. 16)
The value of max-dpb MUST be greater than or equal to the Wherein PicWidthInMbs and FrameHeightInMbs are defined in [1].
value of MaxDPB given in Table A-1 of [1] for the highest
level. Senders MAY use this knowledge to construct coded
video streams with improved compression.
Informative note: This parameter was added primarily to The value of max-dpb MUST be greater than or equal to the value
complement a similar codepoint in the ITU-T of MaxDpbMbs * 3 / 8, wherein the value of MaxDpbMbs is given
Recommendation H.245, so as to facilitate signaling in Table A-1 of [1] for the highest level. Senders MAY use
gateway designs. The decoded picture buffer stores this knowledge to construct coded video streams with improved
reconstructed samples. There is no relationship between compression.
the size of the decoded picture buffer and the buffers
used in RTP, especially de-interleaving and de-jitter
buffers.
max-br: The value of max-br is an integer indicating the maximum Informative note: This parameter was added primarily to
video bit rate in units of 1000 bits per second for the VCL complement a similar codepoint in the ITU-T Recommendation
HRD parameters (see A.3.1 item i of [1]) and in units of 1200 H.245, so as to facilitate signaling gateway designs. The
bits per second for the NAL HRD parameters (see A.3.1 item j decoded picture buffer stores reconstructed samples. There
of [1]). is no relationship between the size of the decoded picture
buffer and the buffers used in RTP, especially
de-interleaving and de-jitter buffers.
The max-br parameter signals that the video decoder of the Informative note: In RFC 3984, which this document
receiver is capable of decoding video at a higher bit rate obsoletes, the unit of this parameter was 1024 bytes. The
than is required by the signaled highest level conveyed in unit has been changed to 8/3 macroblocks in this document.
the value of the profile-level-id parameter or the max-recv- The reason for this change was due to the changes from the
level parameter. 2003 version of the H.264 specification referenced by RFC
3984 to the 2010 version of the H.264 specification
referenced by this document, particularly the changes to
Table A-1 in the H.264 specification due to addition of
color formats and bit depths not supported earlier. The
changed semantics of this parameter keeps backward
compatibility to RFC 3984 and supports all profiles defined
in the 2010 version of the H.264 specification.
When max-br is signaled, the video codec of the receiver MUST max-br: The value of max-br is an integer indicating the maximum
be able to decode NAL unit streams that conform to the video bitrate in units of 1000 bits per second for the VCL HRD
signaled highest level, with the following exceptions in the parameters and in units of 1200 bits per second for the NAL HRD
limits specified by the highest level: parameters. Note that this parameter does not use units of
cpbBrVclFactor and cpbBrNALFactor (see Table A-1 of [1]).
o The value of max-br replaces the MaxBR value in Table A-1 The max-br parameter signals that the video decoder of the
of [1] for the highest level. receiver is capable of decoding video at a higher bitrate than
is required by the signaled highest level conveyed in the value
of the profile-level-id parameter or the max-recv-level
parameter.
o When the max-cpb parameter is not present, the result of When max-br is signaled, the video codec of the receiver MUST
the following formula replaces the value of MaxCPB in be able to decode NAL unit streams that conform to the signaled
Table A-1 of [1]: (MaxCPB of the signaled level) * max-br highest level, with the following exceptions in the limits
/ (MaxBR of the signaled highest level). specified by the highest level:
For example, if a receiver signals capability for Level 1.2 o The value of max-br (after taking cpbBrVclFactor and
with max-br equal to 1550, this indicates a maximum video cpbBrNALFactor into consideration when needed) replaces the
bitrate of 1550 kbits/sec for VCL HRD parameters, a maximum MaxBR value in Table A-1 of [1] for the highest level.
video bitrate of 1860 kbits/sec for NAL HRD parameters, and a
CPB size of 4036458 bits (1550000 / 384000 * 1000 * 1000).
The value of max-br MUST be greater than or equal to the o When the max-cpb parameter is not present, the result of the
value MaxBR given in Table A-1 of [1] for the signaled following formula replaces the value of MaxCPB in Table A-1
highest level. of [1]: (MaxCPB of the signaled level) * max-br / (MaxBR of
the signaled highest level).
Senders MAY use this knowledge to send higher bitrate video For example, if a receiver signals capability for Main profile
as allowed in the level definition of Annex A of H.264, to Level 1.2 with max-br equal to 1550, this indicates a maximum
achieve improved video quality. video bitrate of 1550 kbits/sec for VCL HRD parameters, a
maximum video bitrate of 1860 kbits/sec for NAL HRD parameters,
and a CPB size of 4036458 bits (1550000 / 384000 * 1000 *
1000).
Informative note: This parameter was added primarily to The value of max-br (after taking cpbBrVclFactor and
complement a similar codepoint in the ITU-T cpbBrNALFactor into consideration when needed) MUST be greater
Recommendation H.245, so as to facilitate signaling than or equal to the value MaxBR given in Table A-1 of [1] for
gateway designs. No assumption can be made from the the signaled highest level.
value of this parameter that the network is capable of
handling such bit rates at any given time. In particular,
no conclusion can be drawn that the signaled bit rate is
possible under congestion control constraints.
redundant-pic-cap: Senders MAY use this knowledge to send higher bitrate video as
This parameter signals the capabilities of a receiver allowed in the level definition of Annex A of H.264 to achieve
implementation. When equal to 0, the parameter indicates improved video quality.
that the receiver makes no attempt to use redundant coded
pictures to correct incorrectly decoded primary coded
pictures. When equal to 0, the receiver is not capable of
using redundant slices; therefore, a sender SHOULD avoid
sending redundant slices to save bandwidth. When equal to 1,
the receiver is capable of decoding any such redundant slice
that covers a corrupted area in a primary decoded picture (at
least partly), and therefore a sender MAY send redundant
slices. When the parameter is not present, then a value of 0
MUST be used for redundant-pic-cap. When present, the value
of redundant-pic-cap MUST be either 0 or 1.
When the profile-level-id parameter is present in the same Informative note: This parameter was added primarily to
signaling as the redundant-pic-cap parameter, and the profile complement a similar codepoint in the ITU-T Recommendation
indicated in profile-level-id is such that it disallows the H.245, so as to facilitate signaling gateway designs. The
use of redundant coded pictures (e.g., Main Profile), the assumption that the network is capable of handling such
value of redundant-pic-cap MUST be equal to 0. When a bitrates at any given time cannot be made from the value of
receiver indicates redundant-pic-cap equal to 0, the received this parameter. In particular, no conclusion can be drawn
stream SHOULD NOT contain redundant coded pictures. that the signaled bitrate is possible under congestion
control constraints.
Informative note: Even if redundant-pic-cap is equal to 0, redundant-pic-cap:
the decoder is able to ignore redundant codec pictures This parameter signals the capabilities of a receiver
provided that the decoder supports such a profile implementation. When equal to 0, the parameter indicates that
(Baseline, Extended) in which redundant coded pictures the receiver makes no attempt to use redundant coded pictures
are allowed. to correct incorrectly decoded primary coded pictures. When
equal to 0, the receiver is not capable of using redundant
slices; therefore, a sender SHOULD avoid sending redundant
slices to save bandwidth. When equal to 1, the receiver is
capable of decoding any such redundant slice that covers a
corrupted area in a primary decoded picture (at least partly),
and therefore a sender MAY send redundant slices. When the
parameter is not present, a value of 0 MUST be used for
redundant-pic-cap. When present, the value of redundant-pic-
cap MUST be either 0 or 1.
Informative note: Even if redundant-pic-cap is equal to 1, When the profile-level-id parameter is present in the same
the receiver may also choose other error concealment signaling as the redundant-pic-cap parameter and the profile
strategies to replace or complement decoding of redundant indicated in profile-level-id is such that it disallows the use
slices. of redundant coded pictures (e.g., Main profile), the value of
redundant-pic-cap MUST be equal to 0. When a receiver
indicates redundant-pic-cap equal to 0, the received stream
SHOULD NOT contain redundant coded pictures.
sprop-parameter-sets: Informative note: Even if redundant-pic-cap is equal to 0,
This parameter MAY be used to convey any sequence and picture the decoder is able to ignore redundant codec pictures
parameter set NAL units (herein referred to as the initial provided that the decoder supports a profile (Baseline,
parameter set NAL units) that can be placed in the NAL unit Extended) in which redundant coded pictures are allowed.
stream to precede any other NAL units in decoding order. The
parameter MUST NOT be used to indicate codec capability in
any capability exchange procedure. The value of the
parameter is a comma (',') separated list of base64 [7]
representations of parameter set NAL units as specified in
sections 7.3.2.1 and 7.3.2.2 of [1]. Note that the number of
bytes in a parameter set NAL unit is typically less than 10,
but a picture parameter set NAL unit can contain several
hundreds of bytes.
Informative note: When several payload types are offered Informative note: Even if redundant-pic-cap is equal to 1,
in the SDP Offer/Answer model, each with its own sprop- the receiver may also choose other error concealment
parameter-sets parameter, then the receiver cannot assume strategies to replace or complement decoding of redundant
that those parameter sets do not use conflicting storage slices.
locations (i.e., identical values of parameter set
identifiers). Therefore, a receiver should buffer all
sprop-parameter-sets and make them available to the
decoder instance that decodes a certain payload type.
The "sprop-parameter-sets" parameter MUST only contain sprop-parameter-sets:
parameter sets that are conforming to the profile-level-id, This parameter MAY be used to convey any sequence and picture
i.e., the subset of coding tools indicated by any of the parameter set NAL units (herein referred to as the initial
parameter sets MUST be equal to the default sub-profile, and parameter set NAL units) that can be placed in the NAL unit
the level indicated by any of the parameter sets MUST be stream to precede any other NAL units in decoding order. The
equal to the default level. parameter MUST NOT be used to indicate codec capability in any
capability exchange procedure. The value of the parameter is a
comma-separated (',') list of base64 [7] representations of
parameter set NAL units as specified in Sections 7.3.2.1 and
7.3.2.2 of [1]. Note that the number of bytes in a parameter
set NAL unit is typically less than 10, but a picture parameter
set NAL unit can contain several hundred bytes.
sprop-level-parameter-sets: Informative note: When several payload types are offered in
This parameter MAY be used to convey any sequence and picture the SDP Offer/Answer model, each with its own sprop-
parameter set NAL units (herein referred to as the initial parameter-sets parameter, the receiver cannot assume that
parameter set NAL units) that can be placed in the NAL unit those parameter sets do not use conflicting storage
stream to precede any other NAL units in decoding order and locations (i.e., identical values of parameter set
that are associated with one or more levels different than identifiers). Therefore, a receiver should buffer all
the default level. The parameter MUST NOT be used to sprop-parameter-sets and make them available to the decoder
indicate codec capability in any capability exchange instance that decodes a certain payload type.
procedure.
The sprop-level-parameter-sets parameter contains parameter The sprop-parameter-sets parameter MUST only contain parameter
sets for one or more levels which are different than the sets that are conforming to the profile-level-id, i.e., the
default level. All parameter sets associated with one level subset of coding tools indicated by any of the parameter sets
are clustered and prefixed with a three-byte field which has MUST be equal to the default sub-profile, and the level
the same syntax as profile-level-id. This enables the indicated by any of the parameter sets MUST be equal to the
receiver to install the parameter sets for one level and default level.
discard the rest. The three-byte field is named PLId, and
all parameter sets associated with one level are named PSL,
which has the same syntax as sprop-parameter-sets. Parameter
sets for each level are represented in the form of PLId:PSL,
i.e., PLId followed by a colon (':') and the base64 [7]
representation of the initial parameter set NAL units for the
level. Each pair of PLId:PSL is also separated by a colon.
Note that a PSL can contain multiple parameter sets for that
level, separated with commas (',').
The subset of coding tools indicated by each PLId field MUST sprop-level-parameter-sets:
be equal to the default sub-profile, and the level indicated This parameter MAY be used to convey any sequence and picture
by each PLId field MUST be different than the default level. parameter set NAL units (herein referred to as the initial
All sequence parameter sets contained in each PSL MUST have parameter set NAL units) that can be placed in the NAL unit
the three bytes from profile_idc to level_idc, inclusive, stream to precede any other NAL units in decoding order and
equal to the preceding PLId. that are associated with one or more levels different than the
default level. The parameter MUST NOT be used to indicate
codec capability in any capability exchange procedure.
Informative note: This parameter allows for efficient The sprop-level-parameter-sets parameter contains parameter
level downgrade or upgrade in SDP Offer/Answer and out- sets for one or more levels that are different than the default
of-band transport of parameter sets, simultaneously. level. All parameter sets associated with one level are
clustered and prefixed with a three-byte field that has the
same syntax as profile-level-id. This enables the receiver to
install the parameter sets for one level and discard the rest.
The three-byte field is named PLId, and all parameter sets
associated with one level are named PSL, which has the same
syntax as sprop-parameter-sets. Parameter sets for each level
are represented in the form of PLId:PSL, i.e., PLId followed by
a colon (':') and the base64 [7] representation of the initial
parameter set NAL units for the level. Each pair of PLId:PSLs
is also separated by a colon. Note that a PSL can contain
multiple parameter sets for that level, separated with commas
(',').
use-level-src-parameter-sets: The subset of coding tools indicated by each PLId field MUST be
This parameter MAY be used to indicate a receiver capability. equal to the default sub-profile, and the level indicated by
The value MAY be equal to either 0 or 1. When the parameter each PLId field MUST be different than the default level. All
is not present, the value MUST be inferred to be equal to 0. sequence parameter sets contained in each PSL MUST have the
The value 0 indicates that the receiver does not understand three bytes from profile_idc to level_idc, inclusive, equal to
the sprop-level-parameter-sets parameter, and does not the preceding PLId.
understand the "fmtp" source attribute as specified in
section 6.3 of [9], and will ignore sprop-level-parameter-
sets when present, and will ignore sprop-parameter-sets when
conveyed using the "fmtp" source attribute. The value 1
indicates that the receiver understands the sprop-level-
parameter-sets parameter, and understands the "fmtp" source
attribute as specified in section 6.3 of [9], and is capable
of using parameter sets contained in the sprop-level-
parameter-sets or contained in the sprop-parameter-sets that
is conveyed using the "fmtp" source attribute.
Informative note: An RFC 3984 receiver does not Informative note: This parameter allows for efficient level
understand sprop-level-parameter-sets, use-level-src- downgrade or upgrade in SDP Offer/Answer and out-of-band
parameter-sets, or the "fmtp" source attribute as transport of parameter sets simultaneously.
specified in section 6.3 of [9]. Therefore, during SDP
Offer/Answer, an RFC 3984 receiver as the answerer will
simply ignore sprop-level-parameter-sets, when present in
an offer, and sprop-parameter-sets conveyed using the
"fmtp" source attribute as specified in section 6.3 of
[9]. Assume that the offered payload type was accepted use-level-src-parameter-sets:
at a level lower than the default level. If the offered This parameter MAY be used to indicate a receiver capability.
payload type included sprop-level-parameter-sets or The value MAY be equal to either 0 or 1. When the parameter is
included sprop-parameter-sets conveyed using the "fmtp" not present, the value MUST be inferred to be equal to 0. The
source attribute, and the offerer sees that the answerer value 0 indicates that the receiver does not understand the
has not included use-level-src-parameter-sets equal to 1 sprop-level-parameter-sets parameter, does not understand the
in the answer, the offerer knows that in-band transport "fmtp" source attribute as specified in Section 6.3 of [9],
of parameter sets is needed. will ignore sprop-level-parameter-sets when present, and will
ignore sprop-parameter-sets when conveyed using the "fmtp"
source attribute. The value 1 indicates that the receiver
understands the sprop-level-parameter-sets parameter,
understands the "fmtp" source attribute as specified in Section
6.3 of [9], and is capable of using parameter sets contained in
the sprop-level-parameter-sets or contained in the sprop-
parameter-sets that is conveyed using the "fmtp" source
attribute.
in-band-parameter-sets: Informative note: An RFC 3984 receiver does not understand
This parameter MAY be used to indicate a receiver capability. sprop-level-parameter-sets, use-level-src-parameter-sets, or
The value MAY be equal to either 0 or 1. The value 1 the "fmtp" source attribute as specified in Section 6.3 of
indicates that the receiver discards out-of-band parameter [9]. Therefore, during SDP Offer/Answer, an RFC 3984
sets in sprop-parameter-sets and sprop-level-parameter-sets, receiver as the answerer will simply ignore sprop-level-
therefore the sender MUST transmit all parameter sets in-band. parameter-sets when present in an offer and sprop-parameter-
The value 0 indicates that the receiver utilizes out-of-band sets conveyed using the "fmtp" source attribute, as
parameter sets included in sprop-parameter-sets and/or sprop- specified in Section 6.3 of [9]. Assume that the offered
level-parameter-sets. However, in this case, the sender MAY payload type was accepted at a level lower than the default
still choose to send parameter sets in-band. When in-band- level. If the offered payload type included sprop-level-
parameter-sets is equal to 1, use-level-src-parameter-sets parameter-sets or included sprop-parameter-sets conveyed
MUST NOT be present or MUST be equal to 0. When the using the "fmtp" source attribute and if the offerer sees
parameter is not present, this receiver capability is not that the answerer has not included use-level-src-parameter-
specified, and therefore the sender MAY send out-of-band sets equal to 1 in the answer, the offerer knows that
parameter sets only, or it MAY send in-band-parameter-sets in-band transport of parameter sets is needed.
only, or it MAY send both.
level-asymmetry-allowed: in-band-parameter-sets:
This parameter MAY be used in SDP Offer/Answer to indicate This parameter MAY be used to indicate a receiver capability.
whether level asymmetry, i.e., sending media encoded at a The value MAY be equal to either 0 or 1. The value 1 indicates
different level in the offerer-to-answerer direction than the that the receiver discards out-of-band parameter sets in sprop-
level in the answerer-to-offerer direction, is allowed. The parameter-sets and sprop-level-parameter-sets; therefore, the
value MAY be equal to either 0 or 1. When the parameter is sender MUST transmit all parameter sets in-band. The value 0
not present, the value MUST be inferred to be equal to 0. indicates that the receiver utilizes out-of-band parameter sets
The value 1 in both the offer and the answer indicates that included in sprop-parameter-sets and/or sprop-level-parameter-
level asymmetry is allowed. The value of 0 in either the sets. However, in this case, the sender MAY still choose to
offer or the answer indicates the level asymmetry is not send parameter sets in-band. When in-band-parameter-sets is
allowed. equal to 1, use-level-src-parameter-sets MUST NOT be present or
MUST be equal to 0. When the parameter is not present, this
receiver capability is not specified, and therefore the sender
MAY send out-of-band parameter sets only, it MAY send in-band-
parameter-sets only, or it MAY send both.
If "level-asymmetry-allowed" is equal to 0 (or not present) level-asymmetry-allowed:
in either the offer or the answer, level asymmetry is not This parameter MAY be used in SDP Offer/Answer to indicate
allowed. In this case, the level to use in the direction whether level asymmetry, i.e., sending media encoded at a
from the offerer to the answerer MUST be the same as the different level in the offerer-to-answerer direction than the
level to use in the opposite direction. level in the answerer-to-offerer direction, is allowed. The
value MAY be equal to either 0 or 1. When the parameter is not
present, the value MUST be inferred to be equal to 0. The
value 1 in both the offer and the answer indicates that level
asymmetry is allowed. The value of 0 in either the offer or
the answer indicates that level asymmetry is not allowed.
packetization-mode: If level-asymmetry-allowed is equal to 0 (or not present) in
This parameter signals the properties of an RTP payload type either the offer or the answer, level asymmetry is not allowed.
or the capabilities of a receiver implementation. Only a In this case, the level to use in the direction from the
single configuration point can be indicated; thus, when offerer to the answerer MUST be the same as the level to use in
capabilities to support more than one packetization-mode are the opposite direction.
declared, multiple configuration points (RTP payload types)
must be used.
When the value of packetization-mode is equal to 0 or packetization-mode:
packetization-mode is not present, the single NAL mode MUST This parameter signals the properties of an RTP payload type or
be used. This mode is in use in standards using ITU-T the capabilities of a receiver implementation. Only a single
Recommendation H.241 [3] (see section 12.1). When the value configuration point can be indicated; thus, when capabilities
of packetization-mode is equal to 1, the non-interleaved mode to support more than one packetization-mode are declared,
MUST be used. When the value of packetization-mode is equal multiple configuration points (RTP payload types) must be used.
to 2, the interleaved mode MUST be used. The value of
packetization-mode MUST be an integer in the range of 0 to 2,
inclusive.
sprop-interleaving-depth: When the value of packetization-mode is equal to 0 or
This parameter MUST NOT be present when packetization-mode is packetization-mode is not present, the single NAL mode MUST be
not present or the value of packetization-mode is equal to 0 used. This mode is in use in standards using ITU-T
or 1. This parameter MUST be present when the value of Recommendation H.241 [3] (see Section 12.1). When the value of
packetization-mode is equal to 2. packetization-mode is equal to 1, the non-interleaved mode MUST
be used. When the value of packetization-mode is equal to 2,
the interleaved mode MUST be used. The value of packetization-
mode MUST be an integer in the range of 0 to 2, inclusive.
This parameter signals the properties of an RTP packet stream. sprop-interleaving-depth:
It specifies the maximum number of VCL NAL units that precede This parameter MUST NOT be present when packetization-mode is
any VCL NAL unit in the RTP packet stream in transmission not present or the value of packetization-mode is equal to 0 or
order and follow the VCL NAL unit in decoding order. 1. This parameter MUST be present when the value of
Consequently, it is guaranteed that receivers can reconstruct packetization-mode is equal to 2.
NAL unit decoding order when the buffer size for NAL unit
decoding order recovery is at least the value of sprop-
interleaving-depth + 1 in terms of VCL NAL units.
The value of sprop-interleaving-depth MUST be an integer in This parameter signals the properties of an RTP packet stream.
the range of 0 to 32767, inclusive. It specifies the maximum number of VCL NAL units that precede
any VCL NAL unit in the RTP packet stream in transmission order
and that follow the VCL NAL unit in decoding order.
Consequently, it is guaranteed that receivers can reconstruct
NAL unit decoding order when the buffer size for NAL unit
decoding order recovery is at least the value of sprop-
interleaving-depth + 1 in terms of VCL NAL units.
sprop-deint-buf-req: The value of sprop-interleaving-depth MUST be an integer in the
This parameter MUST NOT be present when packetization-mode is range of 0 to 32767, inclusive.
not present or the value of packetization-mode is equal to 0
or 1. It MUST be present when the value of packetization-
mode is equal to 2.
sprop-deint-buf-req signals the required size of the de- sprop-deint-buf-req:
interleaving buffer for the RTP packet stream. The value of This parameter MUST NOT be present when packetization-mode is
the parameter MUST be greater than or equal to the maximum not present or the value of packetization-mode is equal to 0 or
buffer occupancy (in units of bytes) required in such a de- 1. It MUST be present when the value of packetization-mode is
interleaving buffer that is specified in section 7.2. It is equal to 2.
guaranteed that receivers can perform the de-interleaving of
interleaved NAL units into NAL unit decoding order, when the
de-interleaving buffer size is at least the value of sprop-
deint-buf-req in terms of bytes.
The value of sprop-deint-buf-req MUST be an integer in the sprop-deint-buf-req signals the required size of the
range of 0 to 4294967295, inclusive. de-interleaving buffer for the RTP packet stream. The value of
the parameter MUST be greater than or equal to the maximum
buffer occupancy (in units of bytes) required in such a
de-interleaving buffer that is specified in Section 7.2. It is
guaranteed that receivers can perform the de-interleaving of
interleaved NAL units into NAL unit decoding order, when the
de-interleaving buffer size is at least the value of sprop-
deint-buf-req in terms of bytes.
Informative note: sprop-deint-buf-req indicates the The value of sprop-deint-buf-req MUST be an integer in the
required size of the de-interleaving buffer only. When range of 0 to 4294967295, inclusive.
network jitter can occur, an appropriately sized jitter
buffer has to be provisioned for as well.
deint-buf-cap: Informative note: sprop-deint-buf-req indicates the required
This parameter signals the capabilities of a receiver size of the de-interleaving buffer only. When network
implementation and indicates the amount of de-interleaving jitter can occur, an appropriately sized jitter buffer has
buffer space in units of bytes that the receiver has to be provisioned for as well.
available for reconstructing the NAL unit decoding order. A
receiver is able to handle any stream for which the value of
the sprop-deint-buf-req parameter is smaller than or equal to
this parameter.
If the parameter is not present, then a value of 0 MUST be deint-buf-cap:
used for deint-buf-cap. The value of deint-buf-cap MUST be This parameter signals the capabilities of a receiver
an integer in the range of 0 to 4294967295, inclusive. implementation and indicates the amount of de-interleaving
buffer space in units of bytes that the receiver has available
for reconstructing the NAL unit decoding order. A receiver is
able to handle any stream for which the value of the sprop-
deint-buf-req parameter is smaller than or equal to this
parameter.
Informative note: deint-buf-cap indicates the maximum If the parameter is not present, then a value of 0 MUST be used
possible size of the de-interleaving buffer of the for deint-buf-cap. The value of deint-buf-cap MUST be an
receiver only. When network jitter can occur, an integer in the range of 0 to 4294967295, inclusive.
appropriately sized jitter buffer has to be provisioned
for as well.
sprop-init-buf-time: Informative note: deint-buf-cap indicates the maximum
This parameter MAY be used to signal the properties of an RTP possible size of the de-interleaving buffer of the receiver
packet stream. The parameter MUST NOT be present, if the only. When network jitter can occur, an appropriately sized
value of packetization-mode is equal to 0 or 1. jitter buffer has to be provisioned for as well.
The parameter signals the initial buffering time that a sprop-init-buf-time:
receiver MUST wait before starting decoding to recover the This parameter MAY be used to signal the properties of an RTP
NAL unit decoding order from the transmission order. The packet stream. The parameter MUST NOT be present if the value
parameter is the maximum value of (decoding time of the NAL of packetization-mode is equal to 0 or 1.
unit - transmission time of a NAL unit), assuming reliable
and instantaneous transmission, the same timeline for
transmission and decoding, and that decoding starts when the
first packet arrives.
An example of specifying the value of sprop-init-buf-time The parameter signals the initial buffering time that a
follows. A NAL unit stream is sent in the following receiver MUST wait before starting decoding to recover the NAL
interleaved order, in which the value corresponds to the unit decoding order from the transmission order. The parameter
decoding time and the transmission order is from left to is the maximum value of (decoding time of the NAL unit -
right: transmission time of a NAL unit), assuming reliable and
instantaneous transmission, the same timeline for transmission
and decoding, and commencement of decoding when the first
packet arrives.
0 2 1 3 5 4 6 8 7 ... An example of specifying the value of sprop-init-buf-time
follows. A NAL unit stream is sent in the following
interleaved order, in which the value corresponds to the
decoding time and the transmission order is from left to right:
Assuming a steady transmission rate of NAL units, the 0 2 1 3 5 4 6 8 7 ...
transmission times are:
0 1 2 3 4 5 6 7 8 ... Assuming a steady transmission rate of NAL units, the
transmission times are:
Subtracting the decoding time from the transmission time 0 1 2 3 4 5 6 7 8 ...
column-wise results in the following series:
0 -1 1 0 -1 1 0 -1 1 ... Subtracting the decoding time from the transmission time
column-wise results in the following series:
Thus, in terms of intervals of NAL unit transmission times, 0 -1 1 0 -1 1 0 -1 1 ...
the value of sprop-init-buf-time in this example is 1. The
parameter is coded as a non-negative base10 integer
representation in clock ticks of a 90-kHz clock. If the
parameter is not present, then no initial buffering time
value is defined. Otherwise the value of sprop-init-buf-time
MUST be an integer in the range of 0 to 4294967295, inclusive.
In addition to the signaled sprop-init-buf-time, receivers Thus, in terms of intervals of NAL unit transmission times, the
SHOULD take into account the transmission delay jitter value of sprop-init-buf-time in this example is 1. The
buffering, including buffering for the delay jitter caused by parameter is coded as a non-negative base10 integer
mixers, translators, gateways, proxies, traffic-shapers, and representation in clock ticks of a 90-kHz clock. If the
other network elements. parameter is not present, then no initial buffering time value
is defined. Otherwise, the value of sprop-init-buf-time MUST
be an integer in the range of 0 to 4294967295, inclusive.
sprop-max-don-diff: In addition to the signaled sprop-init-buf-time, receivers
This parameter MAY be used to signal the properties of an RTP SHOULD take into account the transmission delay jitter
packet stream. It MUST NOT be used to signal transmitter or buffering, including buffering for the delay jitter caused by
receiver or codec capabilities. The parameter MUST NOT be mixers, translators, gateways, proxies, traffic-shapers, and
present if the value of packetization-mode is equal to 0 or 1. other network elements.
sprop-max-don-diff is an integer in the range of 0 to 32767,
inclusive. If sprop-max-don-diff is not present, the value
of the parameter is unspecified. sprop-max-don-diff is
calculated as follows:
sprop-max-don-diff = max{AbsDON(i) - AbsDON(j)}, sprop-max-don-diff:
for any i and any j>i, This parameter MAY be used to signal the properties of an RTP
packet stream. It MUST NOT be used to signal transmitter,
receiver, or codec capabilities. The parameter MUST NOT be
present if the value of packetization-mode is equal to 0 or 1.
sprop-max-don-diff is an integer in the range of 0 to 32767,
inclusive. If sprop-max-don-diff is not present, the value of
the parameter is unspecified. sprop-max-don-diff is calculated
as follows:
where i and j indicate the index of the NAL unit in the sprop-max-don-diff = max{AbsDON(i) - AbsDON(j)},
transmission order and AbsDON denotes a decoding order number for any i and any j>i,
of the NAL unit that does not wrap around to 0 after 65535.
In other words, AbsDON is calculated as follows: Let m and n
be consecutive NAL units in transmission order. For the very
first NAL unit in transmission order (whose index is 0),
AbsDON(0) = DON(0). For other NAL units, AbsDON is
calculated as follows:
If DON(m) == DON(n), AbsDON(n) = AbsDON(m) where i and j indicate the index of the NAL unit in the
transmission order and AbsDON denotes a decoding order number
of the NAL unit that does not wrap around to 0 after 65535. In
other words, AbsDON is calculated as follows: let m and n be
consecutive NAL units in transmission order. For the very
first NAL unit in transmission order (whose index is 0),
AbsDON(0) = DON(0). For other NAL units, AbsDON is calculated
as follows:
If (DON(m) < DON(n) and DON(n) - DON(m) < 32768), If DON(m) == DON(n), AbsDON(n) = AbsDON(m)
AbsDON(n) = AbsDON(m) + DON(n) - DON(m)
If (DON(m) > DON(n) and DON(m) - DON(n) >= 32768), If (DON(m) < DON(n) and DON(n) - DON(m) < 32768),
AbsDON(n) = AbsDON(m) + 65536 - DON(m) + DON(n) AbsDON(n) = AbsDON(m) + DON(n) - DON(m)
If (DON(m) < DON(n) and DON(n) - DON(m) >= 32768), If (DON(m) > DON(n) and DON(m) - DON(n) >= 32768),
AbsDON(n) = AbsDON(m) - (DON(m) + 65536 - DON(n)) AbsDON(n) = AbsDON(m) + 65536 - DON(m) + DON(n)
If (DON(m) > DON(n) and DON(m) - DON(n) < 32768), If (DON(m) < DON(n) and DON(n) - DON(m) >= 32768),
AbsDON(n) = AbsDON(m) - (DON(m) - DON(n)) AbsDON(n) = AbsDON(m) - (DON(m) + 65536 - DON(n))
where DON(i) is the decoding order number of the NAL unit If (DON(m) > DON(n) and DON(m) - DON(n) < 32768),
having index i in the transmission order. The decoding order AbsDON(n) = AbsDON(m) - (DON(m) - DON(n))
number is specified in section 5.5.
Informative note: Receivers may use sprop-max-don-diff to where DON(i) is the decoding order number of the NAL unit
trigger which NAL units in the receiver buffer can be having index i in the transmission order. The decoding order
passed to the decoder. number is specified in Section 5.5.
max-rcmd-nalu-size: Informative note: Receivers may use sprop-max-don-diff to
This parameter MAY be used to signal the capabilities of a trigger which NAL units in the receiver buffer can be passed
receiver. The parameter MUST NOT be used for any other to the decoder.
purposes. The value of the parameter indicates the largest
NALU size in bytes that the receiver can handle efficiently.
The parameter value is a recommendation, not a strict upper
boundary. The sender MAY create larger NALUs but must be
aware that the handling of these may come at a higher cost
than NALUs conforming to the limitation.
The value of max-rcmd-nalu-size MUST be an integer in the max-rcmd-nalu-size:
range of 0 to 4294967295, inclusive. If this parameter is This parameter MAY be used to signal the capabilities of a
not specified, no known limitation to the NALU size exists. receiver. The parameter MUST NOT be used for any other
Senders still have to consider the MTU size available between purposes. The value of the parameter indicates the largest
the sender and the receiver and SHOULD run MTU discovery for NALU size in bytes that the receiver can handle efficiently.
this purpose. The parameter value is a recommendation, not a strict upper
boundary. The sender MAY create larger NALUs but must be aware
that the handling of these may come at a higher cost than NALUs
conforming to the limitation.
This parameter is motivated by, for example, an IP to H.223 The value of max-rcmd-nalu-size MUST be an integer in the range
video telephony gateway, where NALUs smaller than the H.223 of 0 to 4294967295, inclusive. If this parameter is not
transport data unit will be more efficient. A gateway may specified, no known limitation to the NALU size exists.
terminate IP; thus, MTU discovery will normally not work Senders still have to consider the MTU size available between
beyond the gateway. the sender and the receiver and SHOULD run MTU discovery for
this purpose.
Informative note: Setting this parameter to a lower than This parameter is motivated by, for example, an IP to H.223
necessary value may have a negative impact. video telephony gateway, where NALUs smaller than the H.223
transport data unit will be more efficient. A gateway may
terminate IP; thus, MTU discovery will normally not work beyond
the gateway.
sar-understood: Informative note: Setting this parameter to a lower than
This parameter MAY be used to indicate a receiver capability necessary value may have a negative impact.
and not anything else. The parameter indicates the maximum
value of aspect_ratio_idc (specified in [1]) smaller than 255
that the receiver understands. Table E-1 of [1] specifies
aspect_ratio_idc equal to 0 as "unspecified", 1 to 16,
inclusive, as specific Sample Aspect Ratios (SARs), 17 to 254,
inclusive, as "reserved", and 255 as the Extended SAR, for
which SAR width and SAR height are explicitly signaled.
Therefore, a receiver with a decoder according to [1]
understands aspect_ratio_idc in the range of 1 to 16,
inclusive and aspect_ratio_idc equal to 255, in the sense
that the receiver knows what exactly the SAR is. For such a
receiver, the value of sar-understood is 16. If in the
future Table E-1 of [1] is extended, e.g., such that the SAR
for aspect_ratio_idc equal to 17 is specified, then for a
receiver with a decoder that understands the extension, the
value of sar-understood is 17. For a receiver with a decoder
according to the 2003 version of [1], the value of sar-
understood is 13, as the minimum reserved aspect_ratio_idc
therein is 14.
When sar-understood is not present, the value MUST be sar-understood:
inferred to be equal to 13. This parameter MAY be used to indicate a receiver capability
and nothing else. The parameter indicates the maximum value of
aspect_ratio_idc (specified in [1]) smaller than 255 that the
receiver understands. Table E-1 of [1] specifies
aspect_ratio_idc equal to 0 as "unspecified"; 1 to 16,
inclusive, as specific Sample Aspect Ratios (SARs); 17 to 254,
inclusive, as "reserved"; and 255 as the Extended SAR, for
which SAR width and SAR height are explicitly signaled.
Therefore, a receiver with a decoder according to [1]
understands aspect_ratio_idc in the range of 1 to 16,
inclusive, and aspect_ratio_idc equal to 255, in the sense that
the receiver knows exactly what the SAR is. For such a
receiver, the value of sar-understood is 16. In the future, if
Table E-1 of [1] is extended, e.g., such that the SAR for
aspect_ratio_idc equal to 17 is specified, then for a receiver
with a decoder that understands the extension, the value of
sar-understood is 17. For a receiver with a decoder according
to the 2003 version of [1], the value of sar-understood is 13,
as the minimum reserved aspect_ratio_idc therein is 14.
sar-supported: When sar-understood is not present, the value MUST be inferred
This parameter MAY be used to indicate a receiver capability to be equal to 13.
and not anything else. The value of this parameter is an
integer in the range of 1 to sar-understood, inclusive, equal
to 255. The value of sar-supported equal to N smaller than
255 indicates that the receiver supports all the SARs
corresponding to H.264 aspect_ratio_idc values (see Table E-1
of [1]) in the range from 1 to N, inclusive, without
geometric distortion. The value of sar-supported equal to
255 indicates that the receiver supports all sample aspect
ratios which are expressible using two 16-bit integer values
as the numerator and denominator, i.e., those that are
expressible using the H.264 aspect_ratio_idc value of 255
(Extended_SAR, see Table E-1 of [1]), without geometric
distortion.
H.264 compliant encoders SHOULD NOT send an aspect_ratio_idc sar-supported:
equal to 0, or an aspect_ratio_idc larger than sar-understood This parameter MAY be used to indicate a receiver capability
and smaller than 255. H.264 compliant encoders SHOULD send and nothing else. The value of this parameter is an integer in
an aspect_ratio_idc that the receiver is able to display the range of 1 to sar-understood, inclusive, equal to 255. The
without geometrical distortion. However, H.264 compliant value of sar-supported equal to N smaller than 255 indicates
encoders MAY choose to send pictures using any SAR. that the receiver supports all the SARs corresponding to H.264
aspect_ratio_idc values (see Table E-1 of [1]) in the range
from 1 to N, inclusive, without geometric distortion. The
value of sar-supported equal to 255 indicates that the receiver
supports all sample aspect ratios that are expressible using
two 16-bit integer values as the numerator and denominator,
i.e., those that are expressible using the H.264
aspect_ratio_idc value of 255 (Extended_SAR, see Table E-1 of
[1]), without geometric distortion.
Note that the actual sample aspect ratio or extended sample H.264-compliant encoders SHOULD NOT send an aspect_ratio_idc
aspect ratio, when present, of the stream is conveyed in the equal to 0 or an aspect_ratio_idc larger than sar-understood
Video Usability Information (VUI) part of the sequence and smaller than 255. H.264-compliant encoders SHOULD send an
parameter set. aspect_ratio_idc that the receiver is able to display without
geometrical distortion. However, H.264-compliant encoders MAY
choose to send pictures using any SAR.
Encoding considerations: Note that the actual sample aspect ratio or extended sample
This type is only defined for transfer via RTP (RFC 3550). aspect ratio, when present, of the stream is conveyed in the
Video Usability Information (VUI) part of the sequence
parameter set.
Security considerations: Encoding considerations:
See section 9 of RFC xxxx. This type is only defined for transfer via RTP (RFC 3550).
Public specification: Security considerations:
Please refer to RFC xxxx and its section 15. See Section 9 of RFC 6184.
Additional information: Public specification:
None Please refer to RFC 6184 and its Section 17.
File extensions: none Additional information:
None
Macintosh file type code: none File extensions: none
Macintosh file type code: none
Object identifier or OID: none Object identifier or OID: none
Person & email address to contact for further information: Person & email address to contact for further information:
Ye-Kui Wang, yekuiwang@huawei.com Ye-Kui Wang, yekui.wang@huawei.com
Intended usage: COMMON Intended usage: COMMON
Author: Author:
Ye-Kui Wang, yekuiwang@huawei.com Ye-Kui Wang, yekui.wang@huawei.com
Change controller: Change controller:
IETF Audio/Video Transport working group delegated from the IETF Audio/Video Transport working group delegated from the
IESG. IESG.
8.2. SDP Parameters 8.2. SDP Parameters
The receiver MUST ignore any parameter unspecified in this memo. The receiver MUST ignore any parameter unspecified in this memo.
8.2.1. Mapping of Payload Type Parameters to SDP 8.2.1. Mapping of Payload Type Parameters to SDP
The media type video/H264 string is mapped to fields in the Session The media type video/H264 string is mapped to fields in the Session
Description Protocol (SDP) [6] as follows: Description Protocol (SDP) [6] as follows:
o The media name in the "m=" line of SDP MUST be video. o The media name in the "m=" line of SDP MUST be video.
o The encoding name in the "a=rtpmap" line of SDP MUST be H264 o The encoding name in the "a=rtpmap" line of SDP MUST be H264 (the
(the media subtype). media subtype).
o The clock rate in the "a=rtpmap" line MUST be 90000. o The clock rate in the "a=rtpmap" line MUST be 90000.
o The OPTIONAL parameters "profile-level-id", "max-recv-level", o The OPTIONAL parameters profile-level-id, max-recv-level, max-
"max-mbps", "max-smbps", "max-fs", "max-cpb", "max-dpb", "max- mbps, max-smbps, max-fs, max-cpb, max-dpb, max-br, redundant-pic-
br", "redundant-pic-cap", "use-level-src-parameter-sets", "in- cap, use-level-src-parameter-sets, in-band-parameter-sets, level-
band-parameter-sets", "level-asymmetry-allowed", "packetization- asymmetry-allowed, packetization-mode, sprop-interleaving-depth,
mode", "sprop-interleaving-depth", "sprop-deint-buf-req", sprop-deint-buf-req, deint-buf-cap, sprop-init-buf-time, sprop-
"deint-buf-cap", "sprop-init-buf-time", "sprop-max-don-diff", max-don-diff, max-rcmd-nalu-size, sar-understood, and sar-
"max-rcmd-nalu-size", "sar-understood", and "sar-supported", supported, when present, MUST be included in the "a=fmtp" line of
when present, MUST be included in the "a=fmtp" line of SDP. SDP. These parameters are expressed as a media type string, in
These parameters are expressed as a media type string, in the the form of a semicolon-separated list of parameter=value pairs.
form of a semicolon separated list of parameter=value pairs.
o The OPTIONAL parameters "sprop-parameter-sets" and "sprop-level- o The OPTIONAL parameters sprop-parameter-sets and sprop-level-
parameter-sets", when present, MUST be included in the "a=fmtp" parameter-sets, when present, MUST be included in the "a=fmtp"
line of SDP or conveyed using the "fmtp" source attribute as line of SDP or conveyed using the "fmtp" source attribute as
specified in section 6.3 of [9]. For a particular media format specified in Section 6.3 of [9]. For a particular media format
(i.e., RTP payload type), a "sprop-parameter-sets" or "sprop- (i.e., RTP payload type), a sprop-parameter-sets or sprop-level-
level-parameter-sets" MUST NOT be both included in the "a=fmtp" parameter-sets MUST NOT be both included in the "a=fmtp" line of
line of SDP and conveyed using the "fmtp" source attribute. SDP and conveyed using the "fmtp" source attribute. When included
When included in the "a=fmtp" line of SDP, these parameters are in the "a=fmtp" line of SDP, these parameters are expressed as a
expressed as a media type string, in the form of a semicolon media type string, in the form of a semicolon-separated list of
separated list of parameter=value pairs. When conveyed using parameter=value pairs. When conveyed using the "fmtp" source
the "fmtp" source attribute, these parameters are only attribute, these parameters are only associated with the given
associated with the given source and payload type as parts of source and payload type as parts of the "fmtp" source attribute.
the "fmtp" source attribute.
Informative note: Conveyance of "sprop-parameter-sets" and Informative note: Conveyance of sprop-parameter-sets and sprop-
"sprop-level-parameter-sets" using the "fmtp" source level-parameter-sets using the "fmtp" source attribute allows
attribute allows for out-of-band transport of parameter sets for out-of-band transport of parameter sets in topologies like
in topologies like Topo-Video-switch-MCU [29]. Topo-Video-switch-MCU [29].
An example of media representation in SDP is as follows (Baseline An example of media representation in SDP is as follows (Baseline
Profile, Level 3.0, some of the constraints of the Main profile may profile, Level 3.0, some of the constraints of the Main profile may
not be obeyed): not be obeyed):
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; a=fmtp:98 profile-level-id=42A01E;
packetization-mode=1; packetization-mode=1;
sprop-parameter-sets=<parameter sets data> sprop-parameter-sets=<parameter sets data>
8.2.2. Usage with the SDP Offer/Answer Model 8.2.2. Usage with the SDP Offer/Answer Model
When H.264 is offered over RTP using SDP in an Offer/Answer model When H.264 is offered over RTP using SDP in an Offer/Answer model [8]
[8] for negotiation for unicast usage, the following limitations for negotiation for unicast usage, the following limitations and
and rules apply: rules apply:
o The parameters identifying a media format configuration for o The parameters identifying a media format configuration for H.264
H.264 are "profile-level-id" and "packetization-mode". These are profile-level-id and packetization-mode. These media format
media format configuration parameters (except for the level part configuration parameters (except for the level part of profile-
of "profile-level-id") MUST be used symmetrically; i.e., the level-id) MUST be used symmetrically; that is, the answerer MUST
answerer MUST either maintain all configuration parameters or either maintain all configuration parameters or remove the media
remove the media format (payload type) completely, if one or format (payload type) completely if one or more of the parameter
more of the parameter values are not supported. Note that the values are not supported. Note that the level part of profile-
level part of "profile-level-id" includes level_idc, and, for level-id includes level_idc, and, for indication of Level 1b when
indication of level 1b when profile_idc is equal to 66, 77 or 88, profile_idc is equal to 66, 77, or 88, bit 4
bit 4 (constraint_set3_flag) of profile-iop. The level part of (constraint_set3_flag) of profile-iop. The level part of profile-
"profile-level-id" is changeable. level-id is changeable.
Informative note: The requirement for symmetric use does not Informative note: The requirement for symmetric use does not
apply for the level part of "profile-level-id", and does not apply for the level part of profile-level-id and does not apply
apply for the other stream properties and capability for the other stream properties and capability parameters.
parameters.
Informative note: In H.264 [1], all the levels except for Informative note: In H.264 [1], all the levels except for Level
level 1b are equal to the value of level_idc divided by 10. 1b are equal to the value of level_idc divided by 10. Level 1b
Level 1b is a level higher than level 1.0 but lower than is a level higher than Level 1.0 but lower than Level 1.1 and
level 1.1, and is signaled in an ad-hoc manner, due to that is signaled in an ad hoc manner, because the level was
the level was specified after level 1.0 and level 1.1. For specified after Level 1.0 and Level 1.1. For the Baseline,
the Baseline, Main and Extended profiles (with profile_idc Main, and Extended profiles (with profile_idc equal to 66, 77,
equal to 66, 77 and 88, respectively), level 1b is indicated and 88, respectively), Level 1b is indicated by level_idc equal
by level_idc equal to 11 (i.e. same as level 1.1) and to 11 (i.e., same as Level 1.1) and constraint_set3_flag equal
constraint_set3_flag equal to 1. For other profiles, level to 1. For other profiles, Level 1b is indicated by level_idc
1b is indicated by level_idc equal to 9 (but note that level equal to 9 (but note that Level 1b for these profiles are still
1b for these profiles are still higher than level 1, which higher than Level 1, which has level_idc equal to 10 and lower
has level_idc equal to 10, and lower than level 1.1). In SDP than Level 1.1). In SDP Offer/Answer, an answer to an offer
Offer/Answer, an answer to an offer may indicate a level may indicate a level equal to or lower than the level indicated
equal to or lower than the level indicated in the offer. Due in the offer. Due to the ad hoc indication of Level 1b,
to the ad-hoc indication of level 1b, offerers and answerers offerers and answerers must check the value of bit 4
must check the value of bit 4 (constraint_set3_flag) of the (constraint_set3_flag) of the middle octet of the parameter
middle octet of the parameter "profile-level-id", when profile-level-id, when profile_idc is equal to 66, 77, or 88
profile_idc is equal to 66, 77 or 88 and level_idc is equal and level_idc is equal to 11.
to 11.
To simplify handling and matching of these configurations, the To simplify the handling and matching of these configurations, the
same RTP payload type number used in the offer SHOULD also be same RTP payload type number used in the offer SHOULD also be used
used in the answer, as specified in [8]. An answer MUST NOT in the answer, as specified in [8]. An answer MUST NOT contain
contain a payload type number used in the offer unless the the payload type number used in the offer unless the configuration
configuration is exactly the same as in the offer. is exactly the same as in the offer.
Informative note: When an offerer receives an answer, it has Informative note: When an offerer receives an answer, it has to
to compare payload types not declared in the offer based on compare payload types not declared in the offer based on the
the media type (i.e., video/H264) and the above media media type (i.e., video/H264) and the above media configuration
configuration parameters with any payload types it has parameters with any payload types it has already declared.
already declared. This will enable it to determine whether This will enable it to determine whether the configuration in
the configuration in question is new or if it is equivalent question is new or if it is equivalent to configuration already
to configuration already offered, since a different payload offered, since a different payload type number may be used in
type number may be used in the answer. the answer.
o The parameter "max-recv-level", when present, declares the o When present, the parameter max-recv-level declares the highest
highest level supported for receiving. In case "max-recv-level" level supported for receiving. In case max-recv-level is not
is not present, the highest level supported for receiving is present, the highest level supported for receiving is equal to the
equal to the default level indicated by the level part of default level indicated by the level part of profile-level-id.
"profile-level-id". "max-recv-level", when present, MUST be When present, max-recv-level MUST be higher than the default
higher than the default level. level.
o The parameter "level-asymmetry-allowed" indicates whether level o The parameter level-asymmetry-allowed indicates whether level
asymmetry is allowed. asymmetry is allowed.
If "level-asymmetry-allowed" is equal to 0 (or not present) in If level-asymmetry-allowed is equal to 0 (or not present) in
either the offer or the answer, level asymmetry is not allowed. either the offer or the answer, level asymmetry is not allowed.
In this case, the level to use in the direction from the offerer In this case, the level to use in the direction from the offerer
to the answerer MUST be the same as the level to use in the to the answerer MUST be the same as the level to use in the
opposite direction, and the common level to use is equal to the opposite direction, and the common level to use is equal to the
lower value of the default level in the offer and the default lower value of the default level in the offer and the default
level in the answer. level in the answer.
Otherwise ("level-asymmetry-allowed" equals to 1 in both the Otherwise, level-asymmetry-allowed equals 1 in both the offer and
offer and the answer), level asymmetry is allowed. In this case, the answer, and level asymmetry is allowed. In this case, the
the level to use in the offerer-to-answerer direction MUST be level to use in the offerer-to-answerer direction MUST be equal to
equal to the highest level the answerer supports for receiving, the highest level the answerer supports for receiving, and the
and the level to use in the answerer-to-offerer direction MUST level to use in the answerer-to-offerer direction MUST be equal to
be equal to the highest level the offerer supports for receiving. the highest level the offerer supports for receiving.
When level asymmetry is not allowed, level upgrade is not When level asymmetry is not allowed, level upgrade is not allowed,
allowed, i.e. the default level in the answer MUST be equal to i.e., the default level in the answer MUST be equal to or lower
or lower than the default level in the offer. than the default level in the offer.
o The parameters "sprop-deint-buf-req", "sprop-interleaving-depth", o The parameters sprop-deint-buf-req, sprop-interleaving-depth,
"sprop-max-don-diff", and "sprop-init-buf-time" describe the sprop-max-don-diff, and sprop-init-buf-time describe the
properties of the RTP packet stream that the offerer or answerer properties of the RTP packet stream that the offerer or answerer
is sending for the media format configuration. This differs is sending for the media format configuration. This differs from
from the normal usage of the Offer/Answer parameters: normally the normal usage of the Offer/Answer parameters: normally such
such parameters declare the properties of the stream that the parameters declare the properties of the stream that the offerer
offerer or the answerer is able to receive. When dealing with or the answerer is able to receive. When dealing with H.264, the
H.264, the offerer assumes that the answerer will be able to offerer assumes that the answerer will be able to receive media
receive media encoded using the configuration being offered. encoded using the configuration being offered.
Informative note: The above parameters apply for any stream Informative note: The above parameters apply for any stream
sent by the declaring entity with the same configuration; sent by a declaring entity with the same configuration; i.e.,
i.e., they are dependent on their source. Rather than being they are dependent on their source. Rather than being bound to
bound to the payload type, the values may have to be applied the payload type, the values may have to be applied to another
to another payload type when being sent, as they apply for payload type when being sent, as they apply for the
the configuration. configuration.
o The capability parameters "max-mbps", "max-smbps", "max-fs", o The capability parameters max-mbps, max-smbps, max-fs, max-cpb,
"max-cpb", "max-dpb", "max-br", ,"redundant-pic-cap", "max-rcmd- max-dpb, max-br, redundant-pic-cap, max-rcmd-nalu-size, sar-
nalu-size", "sar-understood", "sar-supported" MAY be used to understood, and sar-supported MAY be used to declare further
declare further capabilities of the offerer or answerer for capabilities of the offerer or answerer for receiving. These
receiving. These parameters MUST NOT be present when the parameters MUST NOT be present when the direction attribute is
direction attribute is sendonly, and the parameters describe the "sendonly" and when the parameters describe the limitations of
limitations of what the offerer or answerer accepts for what the offerer or answerer accepts for receiving streams.
receiving streams.
o An offerer has to include the size of the de-interleaving buffer, o An offerer has to include the size of the de-interleaving buffer,
"sprop-deint-buf-req", in the offer for an interleaved H.264 sprop-deint-buf-req, in the offer for an interleaved H.264 stream.
stream. To enable the offerer and answerer to inform each other To enable the offerer and answerer to inform each other about
about their capabilities for de-interleaving buffering in their capabilities for de-interleaving buffering in receiving
receiving streams, both parties are RECOMMENDED to include streams, both parties are RECOMMENDED to include deint-buf-cap.
"deint-buf-cap". For interleaved streams, it is also For interleaved streams, it is also RECOMMENDED to consider
RECOMMENDED to consider offering multiple payload types with offering multiple payload types with different buffering
different buffering requirements when the capabilities of the requirements when the capabilities of the receiver are unknown.
receiver are unknown.
o The "sprop-parameter-sets" or "sprop-level-parameter-sets" o The sprop-parameter-sets or sprop-level-parameter-sets parameter,
parameter, when present (included in the "a=fmtp" line of SDP or when present (included in the "a=fmtp" line of SDP or conveyed
conveyed using the "fmtp" source attribute as specified in using the "fmtp" source attribute as specified in Section 6.3 of
section 6.3 of [9]), is used for out-of-band transport of
parameter sets. However, when out-of-band transport of [9]), is used for out-of-band transport of parameter sets.
parameter sets is used, parameter sets MAY still be additionally However, when out-of-band transport of parameter sets is used,
transported in-band. parameter sets MAY still be additionally transported in-band.
The answerer MAY use either out-of-band or in-band transport of The answerer MAY use either out-of-band or in-band transport of
parameter sets for the stream it is sending, regardless of parameter sets for the stream it is sending, regardless of whether
whether out-of-band parameter sets transport has been used in out-of-band parameter sets transport has been used in the offerer-
the offerer-to-answerer direction. Parameter sets included in to-answerer direction. Parameter sets included in an answer are
an answer are independent of those parameter sets included in independent of those parameter sets included in the offer, as they
the offer, as they are used for decoding two different video are used for decoding two different video streams, one from the
streams, one from the answerer to the offerer, and the other in answerer to the offerer and the other in the opposite direction.
the opposite direction.
The following rules apply to transport of parameter sets in the The following rules apply to transport of parameter sets in the
offerer-to-answerer direction. offerer-to-answerer direction.
o An offer MAY include either or both of "sprop-parameter- o An offer MAY include either or both of sprop-parameter-sets
sets" and "sprop-level-parameter-sets". If neither "sprop- and sprop-level-parameter-sets. If neither sprop-parameter-
parameter-sets" nor "sprop-level-parameter-sets" is present sets nor sprop-level-parameter-sets is present in the offer,
in the offer, then only in-band transport of parameter sets then only in-band transport of parameter sets is used.
is used.
o If the answer includes "in-band-parameter-sets" equal to 1, o If the answer includes in-band-parameter-sets equal to 1,
then the offerer MUST transmit parameter sets in-band. then the offerer MUST transmit parameter sets in-band.
Otherwise, the following applies. Otherwise, the following applies.
o If the level to use in the offerer-to-answerer o If the level to use in the offerer-to-answerer
direction is equal to the default level in the offer, direction is equal to the default level in the offer,
the following applies. the following applies.
When there is a "sprop-parameter-sets" included When there is a sprop-parameter-sets included in
in the "a=fmtp" line in the offer, the answerer the "a=fmtp" line in the offer, the answerer MUST
MUST be prepared to use the parameter sets be prepared to use the parameter sets included in
included in the "sprop-parameter-sets" for the sprop-parameter-sets for decoding the incoming
decoding the incoming NAL unit stream. NAL unit stream.
When there is a "sprop-parameter-sets" conveyed When there is a sprop-parameter-sets conveyed using
using the "fmtp" source attribute in the offer, the "fmtp" source attribute in the offer, the
the following applies. If the answer includes following applies. If the answer includes use-
"use-level-src-parameter-sets" equal to 1 or the level-src-parameter-sets equal to 1 or the "fmtp"
"fmtp" source attribute, the answerer MUST be source attribute, the answerer MUST be prepared to
prepared to use the parameter sets included in use the parameter sets included in the sprop-
the "sprop-parameter-sets" for decoding the parameter-sets for decoding the incoming NAL unit
incoming NAL unit stream; Otherwise, the offerer stream; otherwise, the offerer MUST transmit
MUST transmit parameter sets in-band. parameter sets in-band.
When "sprop-parameter-sets" is not present in the When sprop-parameter-sets is not present in the
offer, the offerer MUST transmit parameter sets offer, the offerer MUST transmit parameter sets in-
in-band. band.
The answerer MUST ignore "sprop-level-parameter- The answerer MUST ignore sprop-level-parameter-
sets", when present (either included in the sets, when present (either included in the "a=fmtp"
"a=fmtp" line or conveyed using the "fmtp" source line or conveyed using the "fmtp" source attribute)
attribute) in the offer. in the offer.
o Otherwise (the level to use in the offerer-to-answerer o Otherwise, the level to use in the offerer-to-answerer
direction is not equal to the default level in the direction is not equal to the default level in the
offer), the following applies. offer, and the following applies.
The answerer MUST ignore "sprop-parameter-sets", The answerer MUST ignore sprop-parameter-sets, when
when present (either included in the "a=fmtp" present (either included in the "a=fmtp" line or
line or conveyed using the "fmtp" source conveyed using the "fmtp" source attribute) in the
attribute) in the offer. offer.
When neither "use-level-src-parameter-sets" equal When neither use-level-src-parameter-sets is equal
to 1 nor the "fmtp" source attribute is present to 1 nor the "fmtp" source attribute is present in
in the answer, the answerer MUST ignore "sprop- the answer, the answerer MUST ignore sprop-level-
level-parameter-sets", when present in the offer, parameter-sets, when present in the offer, and the
and the offerer MUST transmit parameter sets in- offerer MUST transmit parameter sets in-band.
band.
When either "use-level-src-parameter-sets" equal When either use-level-src-parameter-sets is equal
to 1 or the "fmtp" source attribute is present in to 1 or the "fmtp" source attribute is present in
the answer, the answerer MUST be prepared to use the answer, the answerer MUST be prepared to use
the parameter sets that are included in "sprop- the parameter sets that are included in sprop-
level-parameter-sets" for the accepted level (i.e. level-parameter-sets for the accepted level (i.e.,
the default level in the answer), when present in the default level in the answer), when present in
the offer, for decoding the incoming NAL unit the offer, for decoding the incoming NAL unit
stream, and ignore all other parameter sets stream, and ignore all other parameter sets
included in "sprop-level-parameter-sets". included in sprop-level-parameter-sets.
When no parameter sets for the level to use in When no parameter sets for the level to use in the
the offerer-to-answerer direction are present in offerer-to-answerer direction are present in sprop-
"sprop-level-parameter-sets" in the offer, the level-parameter-sets in the offer, the offerer MUST
offerer MUST transmit parameter sets in-band. transmit parameter sets in-band.
The following rules apply to transport of parameter sets in the The following rules apply to the transport of parameter sets in
answerer-to-offerer direction. the answerer-to-offerer direction.
o An answer MAY include either "sprop-parameter-sets" or o An answer MAY include either sprop-parameter-sets or sprop-
"sprop-level-parameter-sets", but MUST NOT include both of level-parameter-sets but MUST NOT include both. If neither
the two. If neither "sprop-parameter-sets" nor "sprop- sprop-parameter-sets nor sprop-level-parameter-sets is
level-parameter-sets" is present in the answer, then only present in the answer, then only in-band transport of
in-band transport of parameter sets is used. parameter sets is used.
o If the offer includes "in-band-parameter-sets" equal to 1, o If the offer includes in-band-parameter-sets equal to 1, the
the answerer MUST NOT include "sprop-parameter-sets" or answerer MUST NOT include sprop-parameter-sets or sprop-
"sprop-level-parameter-sets" in the answer and MUST level-parameter-sets in the answer and MUST transmit
transmit parameter sets in-band. Otherwise, the following parameter sets in-band. Otherwise, the following applies.
applies.
o If the level to use in the answerer-to-offerer o If the level to use in the answerer-to-offerer
direction is equal to the default level in the answer, direction is equal to the default level in the answer,
the following applies. the following applies.
When there is a "sprop-parameter-sets" included When there is a sprop-parameter-sets included in
in the "a=fmtp" line in the answer, the offerer the "a=fmtp" line in the answer, the offerer MUST
MUST be prepared to use the parameter sets be prepared to use the parameter sets included in
included in the "sprop-parameter-sets" for the sprop-parameter-sets for decoding the incoming
decoding the incoming NAL unit stream. NAL unit stream.
When there is a "sprop-parameter-sets" conveyed When there is a sprop-parameter-sets conveyed using
using the "fmtp" source attribute in the answer, the "fmtp" source attribute in the answer, the
the following applies. If the offer includes following applies. If the offer includes use-
"use-level-src-parameter-sets" equal to 1 or the level-src-parameter-sets equal to 1 or the "fmtp"
"fmtp" source attribute, the offerer MUST be source attribute, the offerer MUST be prepared to
prepared to use the parameter sets included in use the parameter sets included in the sprop-
the "sprop-parameter-sets" for decoding the parameter-sets for decoding the incoming NAL unit
incoming NAL unit stream; Otherwise, the stream; otherwise, the answerer MUST transmit
answerer MUST transmit parameter sets in-band. parameter sets in-band.
When "sprop-parameter-sets" is not present in the When sprop-parameter-sets is not present in the
answer, the answerer MUST transmit parameter sets answer, the answerer MUST transmit parameter sets
in-band. in-band.
The offerer MUST ignore "sprop-level-parameter- The offerer MUST ignore sprop-level-parameter-sets,
sets", when present (either included in the when present (either included in the "a=fmtp" line
"a=fmtp" line or conveyed using the "fmtp" source or conveyed using the "fmtp" source attribute) in
attribute) in the answer. the answer.
o Otherwise (the level to use in the answerer-to-offerer o Otherwise, the level to use in the answerer-to-offerer
direction is not equal to the default level in the direction is not equal to the default level in the
answer), the following applies. answer, and the following applies.
The offerer MUST ignore "sprop-parameter-sets", The offerer MUST ignore sprop-parameter-sets when
when present (either included in the "a=fmtp" present (either included in the "a=fmtp" line of
line of SDP or conveyed using the "fmtp" source SDP or conveyed using the "fmtp" source attribute)
attribute) in the answer. in the answer.
When neither "use-level-src-parameter-sets" equal When neither use-level-src-parameter-sets is equal
to 1 nor the "fmtp" source attribute is present to 1 nor the "fmtp" source attribute is present in
in the offer, the offerer MUST ignore "sprop- the offer, the offerer MUST ignore sprop-level-
level-parameter-sets", when present, and the parameter-sets, when present, and the answerer MUST
answerer MUST transmit parameter sets in-band. transmit parameter sets in-band.
When either "use-level-src-parameter-sets" equal When either use-level-src-parameter-sets is equal
to 1 or the "fmtp" source attribute is present in to 1 or the "fmtp" source attribute is present in
the offer, the offerer MUST be prepared to use the offer, the offerer MUST be prepared to use the
the parameter sets that are included in "sprop- parameter sets that are included in sprop-level-
level-parameter-sets" for the level to use in the parameter-sets for the level to use in the
answerer-to-offerer direction, when present in answerer-to-offerer direction, when present in the
the answer, for decoding the incoming NAL unit answer, for decoding the incoming NAL unit stream,
stream, and ignore all other parameter sets and ignore all other parameter sets included in
included in "sprop-level-parameter-sets" in the sprop-level-parameter-sets in the answer.
answer.
When no parameter sets for the level to use in When no parameter sets for the level to use in the
the answerer-to-offerer direction are present in answerer-to-offerer direction are present in sprop-
"sprop-level-parameter-sets" in the answer, the level-parameter-sets in the answer, the answerer
answerer MUST transmit parameter sets in-band. MUST transmit parameter sets in-band.
When "sprop-parameter-sets" or "sprop-level-parameter-sets" is When sprop-parameter-sets or sprop-level-parameter-sets is
conveyed using the "fmtp" source attribute as specified in conveyed using the "fmtp" source attribute as specified in Section
section 6.3 of [9], the receiver of the parameters MUST store 6.3 of [9], the receiver of the parameters MUST store the
the parameter sets included in the "sprop-parameter-sets" or parameter sets included in the sprop-parameter-sets or sprop-
"sprop-level-parameter-sets" for the accepted level and level-parameter-sets for the accepted level and associate them
associate them to the source given as a part of the "fmtp" with the source given as a part of the "fmtp" source attribute.
source attribute. Parameter sets associated with one source Parameter sets associated with one source MUST only be used to
MUST only be used to decode NAL units conveyed in RTP packets decode NAL units conveyed in RTP packets from the same source.
from the same source. When this mechanism is in use, SSRC When this mechanism is in use, SSRC collision detection and
collision detection and resolution MUST be performed as resolution MUST be performed as specified in [9].
specified in [9].
Informative note: Conveyance of "sprop-parameter-sets" and Informative note: Conveyance of sprop-parameter-sets and sprop-
"sprop-level-parameter-sets" using the "fmtp" source level-parameter-sets using the "fmtp" source attribute may be
attribute may be used in topologies like Topo-Video-switch- used in topologies like Topo-Video-switch-MCU [29] to enable
MCU [29] to enable out-of-band transport of parameter sets. out-of-band transport of parameter sets.
For streams being delivered over multicast, the following rules For streams being delivered over multicast, the following rules
apply: apply:
o The media format configuration is identified by "profile-level- o The media format configuration is identified by "profile-level-
id", including the level part, and "packetization-mode". These id", including the level part, and packetization-mode. These
media format configuration parameters (including the level part media format configuration parameters (including the level part of
of "profile-level-id") MUST be used symmetrically; i.e., the profile-level-id) MUST be used symmetrically; that is, the
answerer MUST either maintain all configuration parameters or answerer MUST either maintain all configuration parameters or
remove the media format (payload type) completely. Note that remove the media format (payload type) completely. Note that this
this implies that the level part of "profile-level-id" for implies that the level part of profile-level-id for Offer/Answer
Offer/Answer in multicast is not changeable. in multicast is not changeable.
To simplify handling and matching of these configurations, the To simplify the handling and matching of these configurations, the
same RTP payload type number used in the offer SHOULD also be same RTP payload type number used in the offer SHOULD also be used
used in the answer, as specified in [8]. An answer MUST NOT in the answer, as specified in [8]. An answer MUST NOT contain a
contain a payload type number used in the offer unless the payload type number used in the offer unless the configuration is
configuration is the same as in the offer. the same as in the offer.
o Parameter sets received MUST be associated with the originating o Parameter sets received MUST be associated with the originating
source, and MUST be only used in decoding the incoming NAL unit source and MUST only be used in decoding the incoming NAL unit
stream from the same source. stream from the same source.
o The rules for other parameters are the same as above for unicast o The rules for other parameters are the same as above for unicast
as long as the above rules are obeyed. as long as the above rules are obeyed.
Table 6 lists the interpretation of all the media type parameters Table 6 lists the interpretation of all the media type parameters
that MUST be used for the different direction attributes. that MUST be used for the different direction attributes.
Table 6. Interpretation of parameters for different direction Table 6. Interpretation of parameters for different direction
attributes. attributes
sendonly --+ sendonly --+
recvonly --+ | recvonly --+ |
sendrecv --+ | | sendrecv --+ | |
| | | | | |
profile-level-id C C P profile-level-id C C P
max-recv-level R R - max-recv-level R R -
packetization-mode C C P packetization-mode C C P
sprop-deint-buf-req P - P sprop-deint-buf-req P - P
sprop-interleaving-depth P - P sprop-interleaving-depth P - P
skipping to change at page 68, line 5 skipping to change at page 65, line 49
sprop-parameter-sets S - S sprop-parameter-sets S - S
sprop-level-parameter-sets S - S sprop-level-parameter-sets S - S
Legend: Legend:
C: configuration for sending and receiving streams C: configuration for sending and receiving streams
O: offer/answer mode O: offer/answer mode
P: properties of the stream to be sent P: properties of the stream to be sent
R: receiver capabilities R: receiver capabilities
S: out-of-band parameter sets S: out-of-band parameter sets
-: not usable, when present SHOULD be ignored -: not usable (when present, SHOULD be ignored)
Parameters used for declaring receiver capabilities are in general Parameters used for declaring receiver capabilities are in general
downgradable; i.e., they express the upper limit for a sender's downgradable; that is, they express the upper limit for a sender's
possible behavior. Thus a sender MAY select to set its encoder possible behavior. Thus, a sender MAY select to set its encoder
using only lower/less or equal values of these parameters. using only lower/less or equal values of these parameters.
Parameters declaring a configuration point are not changeable, with Parameters declaring a configuration point are not changeable, with
the exception of the level part of the "profile-level-id" parameter the exception of the level part of the profile-level-id parameter for
for unicast usage. These express values a receiver expects to be unicast usage.
used and must be used verbatim on the sender side.
When a sender's capabilities are declared, and non-downgradable When a sender's capabilities are declared and non-downgradable
parameters are used in this declaration, then these parameters parameters are used in this declaration, these parameters express a
express a configuration that is acceptable for the sender to configuration that is acceptable for the sender to receive streams.
receive streams. In order to achieve high interoperability levels, In order to achieve high interoperability levels, it is often
it is often advisable to offer multiple alternative configurations; advisable to offer multiple alternative configurations, e.g., for the
e.g., for the packetization mode. It is impossible to offer packetization mode. It is impossible to offer multiple
multiple configurations in a single payload type. Thus, when configurations in a single payload type. Thus, when multiple
multiple configuration offers are made, each offer requires its own configuration offers are made, each offer requires its own RTP
RTP payload type associated with the offer. payload type associated with the offer.
A receiver SHOULD understand all media type parameters, even if it A receiver SHOULD understand all media type parameters, even if it
only supports a subset of the payload format's functionality. This only supports a subset of the payload format's functionality. This
ensures that a receiver is capable of understanding when an offer ensures that a receiver is capable of understanding when an offer to
to receive media can be downgraded to what is supported by the receive media can be downgraded to what is supported by the receiver
receiver of the offer. of the offer.
An answerer MAY extend the offer with additional media format An answerer MAY extend the offer with additional media format
configurations. However, to enable their usage, in most cases a configurations. However, to enable their usage, in most cases, a
second offer is required from the offerer to provide the stream second offer is required from the offerer to provide the stream
property parameters that the media sender will use. This also has property parameters that the media sender will use. This also has
the effect that the offerer has to be able to receive this media the effect that the offerer has to be able to receive this media
format configuration, not only to send it. format configuration, not only to send it.
If an offerer wishes to have non-symmetric capabilities between If an offerer wishes to have non-symmetric capabilities between
sending and receiving, the offerer can allow asymmetric levels via sending and receiving, the offerer can allow asymmetric levels via
"level-asymmetry-allowed" equal to 1. Alternatively, the offerer level-asymmetry-allowed being equal to 1. Alternatively, the offerer
could offer different RTP sessions; i.e., different media lines could offer different RTP sessions, i.e., different media lines
declared as "recvonly" and "sendonly", respectively. This may have declared as "recvonly" and "sendonly", respectively. This may have
further implications on the system, and may require additional further implications on the system and may require additional
external semantics to associate the two media lines. external semantics to associate the two media lines.
8.2.3. Usage in Declarative Session Descriptions 8.2.3. Usage in Declarative Session Descriptions
When H.264 over RTP is offered with SDP in a declarative style, as When H.264 over RTP is offered with SDP in a declarative style, as in
in RTSP [27] or SAP [28], the following considerations are Real Time Streaming Protocol (RTSP) [27] or Session Announcement
necessary. Protocol (SAP) [28], the following considerations are necessary.
o All parameters capable of indicating both stream properties and o All parameters capable of indicating both stream properties and
receiver capabilities are used to indicate only stream receiver capabilities are used to indicate only stream properties.
properties. For example, in this case, the parameter "profile- For example, in this case, the parameter profile-level-id declares
level-id" declares only the values used by the stream, not the only the values used by the stream, not the capabilities for
capabilities for receiving streams. This results in that the receiving streams. The result of this is that the following
following interpretation of the parameters MUST be used: interpretation of the parameters MUST be used:
Declaring actual configuration or stream properties: Declaring actual configuration or stream properties:
- profile-level-id - profile-level-id
- packetization-mode - packetization-mode
- sprop-interleaving-depth - sprop-interleaving-depth
- sprop-deint-buf-req - sprop-deint-buf-req
- sprop-max-don-diff - sprop-max-don-diff
- sprop-init-buf-time - sprop-init-buf-time
Out-of-band transporting of parameter sets: Out-of-band transporting of parameter sets:
- sprop-parameter-sets - sprop-parameter-sets
- sprop-level-parameter-sets - sprop-level-parameter-sets
Not usable(when present, they SHOULD be ignored): Not usable (when present, they SHOULD be ignored):
- max-mbps - max-mbps
- max-smbps - max-smbps
- max-fs - max-fs
- max-cpb - max-cpb
- max-dpb - max-dpb
- max-br - max-br
- max-recv-level - max-recv-level
- redundant-pic-cap - redundant-pic-cap
- max-rcmd-nalu-size - max-rcmd-nalu-size
- deint-buf-cap - deint-buf-cap
- sar-understood - sar-understood
- sar-supported - sar-supported
- in-band-parameter-sets - in-band-parameter-sets
- level-asymmetry-allowed - level-asymmetry-allowed
- use-level-src-parameter-sets - use-level-src-parameter-sets
o A receiver of the SDP is required to support all parameters and o A receiver of the SDP is required to support all parameters and
values of the parameters provided; otherwise, the receiver MUST values of the parameters provided; otherwise, the receiver MUST
reject (RTSP) or not participate in (SAP) the session. It falls reject (RTSP) or not participate in (SAP) the session. It falls
on the creator of the session to use values that are expected to on the creator of the session to use values that are expected to
be supported by the receiving application. be supported by the receiving application.
8.3. Examples 8.3. Examples
An SDP Offer/Answer exchange wherein both parties are expected to An SDP Offer/Answer exchange wherein both parties are expected to
both send and receive could look like the following. Only the both send and receive could look like the following. Only the media-
media codec specific parts of the SDP are shown. Some lines are codec-specific parts of the SDP are shown. Some lines are wrapped
wrapped due to text constraints. due to text constraints.
Offerer -> Answerer SDP message: Offerer -> Answerer SDP message:
m=video 49170 RTP/AVP 100 99 98 m=video 49170 RTP/AVP 100 99 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; packetization-mode=0; a=fmtp:98 profile-level-id=42A01E; packetization-mode=0;
sprop-parameter-sets=<parameter sets data#0> sprop-parameter-sets=<parameter sets data#0>
a=rtpmap:99 H264/90000 a=rtpmap:99 H264/90000
a=fmtp:99 profile-level-id=42A01E; packetization-mode=1; a=fmtp:99 profile-level-id=42A01E; packetization-mode=1;
sprop-parameter-sets=<parameter sets data#1> sprop-parameter-sets=<parameter sets data#1>
a=rtpmap:100 H264/90000 a=rtpmap:100 H264/90000
a=fmtp:100 profile-level-id=42A01E; packetization-mode=2; a=fmtp:100 profile-level-id=42A01E; packetization-mode=2;
sprop-parameter-sets=<parameter sets data#2>; sprop-parameter-sets=<parameter sets data#2>;
sprop-interleaving-depth=45; sprop-deint-buf-req=64000; sprop-interleaving-depth=45; sprop-deint-buf-req=64000;
sprop-init-buf-time=102478; deint-buf-cap=128000 sprop-init-buf-time=102478; deint-buf-cap=128000
The above offer presents the same codec configuration in three The above offer presents the same codec configuration in three
different packetization formats. PT 98 represents single NALU mode, different packetization formats. Payload type 98 represents single
PT 99 represents non-interleaved mode, and PT 100 indicates the NALU mode, payload type 99 represents non-interleaved mode, and
interleaved mode. In the interleaved mode case, the interleaving payload type 100 indicates the interleaved mode. In the interleaved
parameters that the offerer would use if the answer indicates mode case, the interleaving parameters that the offerer would use if
support for PT 100 are also included. In all three cases the the answer indicates support for payload type 100 are also included.
parameter "sprop-parameter-sets" conveys the initial parameter sets In all three cases, the parameter sprop-parameter-sets conveys the
that are required by the answerer when receiving a stream from the initial parameter sets that are required by the answerer when
offerer when this configuration is accepted. Note that the value receiving a stream from the offerer when this configuration is
for "sprop-parameter-sets" could be different for each payload type. accepted. Note that the value for sprop-parameter-sets could be
different for each payload type.
Answerer -> Offerer SDP message: Answerer -> Offerer SDP message:
m=video 49170 RTP/AVP 100 99 97 m=video 49170 RTP/AVP 100 99 97
a=rtpmap:97 H264/90000 a=rtpmap:97 H264/90000
a=fmtp:97 profile-level-id=42A01E; packetization-mode=0; a=fmtp:97 profile-level-id=42A01E; packetization-mode=0;
sprop-parameter-sets=<parameter sets data#3> sprop-parameter-sets=<parameter sets data#3>
a=rtpmap:99 H264/90000 a=rtpmap:99 H264/90000
a=fmtp:99 profile-level-id=42A01E; packetization-mode=1; a=fmtp:99 profile-level-id=42A01E; packetization-mode=1;
sprop-parameter-sets=<parameter sets data#4>; sprop-parameter-sets=<parameter sets data#4>;
max-rcmd-nalu-size=3980 max-rcmd-nalu-size=3980
a=rtpmap:100 H264/90000 a=rtpmap:100 H264/90000
a=fmtp:100 profile-level-id=42A01E; packetization-mode=2; a=fmtp:100 profile-level-id=42A01E; packetization-mode=2;
sprop-parameter-sets=<parameter sets data#5>; sprop-parameter-sets=<parameter sets data#5>;
sprop-interleaving-depth=60; sprop-interleaving-depth=60;
sprop-deint-buf-req=86000; sprop-init-buf-time=156320; sprop-deint-buf-req=86000; sprop-init-buf-time=156320;
deint-buf-cap=128000; max-rcmd-nalu-size=3980 deint-buf-cap=128000; max-rcmd-nalu-size=3980
As the Offer/Answer negotiation covers both sending and receiving As the Offer/Answer negotiation covers both sending and receiving
streams, an offer indicates the exact parameters for what the streams, an offer indicates the exact parameters for what the offerer
offerer is willing to receive, whereas the answer indicates the is willing to receive, whereas the answer indicates the same for what
same for what the answerer accepts to receive. In this case the the answerer is willing to receive. In this case, the offerer
offerer declared that it is willing to receive payload type 98. declared that it is willing to receive payload type 98. The answerer
The answerer accepts this by declaring an equivalent payload type accepts this by declaring an equivalent payload type 97; that is, it
97; i.e., it has identical values for the two parameters "profile- has identical values for the two parameters profile-level-id and
level-id" and "packetization-mode" (since "packetization-mode" is packetization-mode (since packetization-mode is equal to 0 and sprop-
equal to 0, "sprop-deint-buf-req" is not present). As the offered deint-buf-req is not present). As the offered payload type 98 is
payload type 98 is accepted, the answerer needs to store parameter accepted, the answerer needs to store parameter sets included in
sets included in sprop-parameter-sets=<parameter sets data#0> in sprop-parameter-sets=<parameter sets data#0> in case the offer
case the offer finally decides to use this configuration. In the finally decides to use this configuration. In the answer, the
answer, the answerer includes the parameter sets in sprop- answerer includes the parameter sets in sprop-parameter-
parameter-sets=<parameter sets data#3> that the answerer would use sets=<parameter sets data#3> that the answerer would use in the
in the stream sent from the answerer if this configuration is stream sent from the answerer if this configuration is finally used.
finally used.
The answerer also accepts the reception of the two configurations The answerer also accepts the reception of the two configurations
that payload types 99 and 100 represent. Again, the answerer needs that payload types 99 and 100 represent. Again, the answerer needs
to store parameter sets included in sprop-parameter-sets=<parameter to store parameter sets included in sprop-parameter-sets=<parameter
sets data#1> and sprop-parameter-sets=<parameter sets data#2> in sets data#1> and sprop-parameter-sets=<parameter sets data#2> in case
case the offer finally decides to use either of these two the offer finally decides to use either of these two configurations.
configurations. The answerer provides the initial parameter sets The answerer provides the initial parameter sets for the answerer-to-
for the answerer-to-offerer direction, i.e. the parameter sets in offerer direction, i.e., the parameter sets in sprop-parameter-
sprop-parameter-sets=<parameter sets data#4> and sprop-parameter- sets=<parameter sets data#4> and sprop-parameter-sets=<parameter sets
sets=<parameter sets data#5>, for payload types 99 and 100, data#5>, for payload types 99 and 100, respectively, that it will use
respectively, that it will use to send the payload types. The to send the payload types. The answerer also provides the offerer
answerer also provides the offerer with its memory limit for de- with its memory limit for de-interleaving operations by providing a
interleaving operations by providing a "deint-buf-cap" parameter. deint-buf-cap parameter. This is only useful if the offerer decides
This is only useful if the offerer decides on making a second offer, on making a second offer, where it can take the new value into
where it can take the new value into account. The "max-rcmd-nalu- account. The max-rcmd-nalu-size indicates that the answerer can
size" indicates that the answerer can efficiently process NALUs up efficiently process NALUs up to the size of 3980 bytes. However,
to the size of 3980 bytes. However, there is no guarantee that the there is no guarantee that the network supports this size.
network supports this size.
In the following example, the offer is accepted without level In the following example, the offer is accepted without level
downgrading (i.e. the default level, 3.0, is accepted), and both downgrading (i.e., the default level, Level 3.0, is accepted), and
"sprop-parameter-sets" and "sprop-level-parameter-sets" are present both sprop-parameter-sets and sprop-level-parameter-sets are present
in the offer. The answerer must ignore sprop-level-parameter- in the offer. The answerer must ignore sprop-level-parameter-
sets=<parameter sets data#1> and store parameter sets in sprop- sets=<parameter sets data#1> and store parameter sets in sprop-
parameter-sets=<parameter sets data#0> for decoding the incoming parameter-sets=<parameter sets data#0> for decoding the incoming NAL
NAL unit stream. The offerer must store the parameter sets in unit stream. The offerer must store the parameter sets in sprop-
sprop-parameter-sets=<parameter sets data#2> in the answer for parameter-sets=<parameter sets data#2> in the answer for decoding the
decoding the incoming NAL unit stream. Note that in this example, incoming NAL unit stream. Note that in this example, parameter sets
parameter sets in sprop-parameter-sets=<parameter sets data#2> must in sprop-parameter-sets=<parameter sets data#2> must be associated
be associated with level 3.0. with Level 3.0.
Offer SDP: Offer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0
packetization-mode=1; packetization-mode=1;
sprop-parameter-sets=<parameter sets data#0>; sprop-parameter-sets=<parameter sets data#0>;
sprop-level-parameter-sets=<parameter sets data#1> sprop-level-parameter-sets=<parameter sets data#1>
Answer SDP: Answer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0
packetization-mode=1; packetization-mode=1;
sprop-parameter-sets=<parameter sets data#2> sprop-parameter-sets=<parameter sets data#2>
In the following example, the offer (Baseline profile, level 1.1) In the following example, the offer (Baseline profile, Level 1.1) is
is accepted with level downgrading (the accepted level is 1b), and accepted with level downgrading (the accepted level is Level 1b), and
both "sprop-parameter-sets" and "sprop-level-parameter-sets" are both sprop-parameter-sets and sprop-level-parameter-sets are present
present in the offer. The answerer must ignore sprop-parameter- in the offer. The answerer must ignore sprop-parameter-
sets=<parameter sets data#0> and all parameter sets not for the sets=<parameter sets data#0> and all parameter sets not for the
accepted level (level 1b) in sprop-level-parameter-sets=<parameter accepted level (Level 1b) in sprop-level-parameter-sets=<parameter
sets data#1>, and must store parameter sets for the accepted level sets data#1> and must store parameter sets for the accepted level
(level 1b) in sprop-level-parameter-sets=<parameter sets data#1> (Level 1b) in sprop-level-parameter-sets=<parameter sets data#1> for
for decoding the incoming NAL unit stream. The offerer must store decoding the incoming NAL unit stream. The offerer must store the
the parameter sets in sprop-parameter-sets=<parameter sets data#2> parameter sets in sprop-parameter-sets=<parameter sets data#2> in the
in the answer for decoding the incoming NAL unit stream. Note that answer for decoding the incoming NAL unit stream. Note that in this
in this example, parameter sets in sprop-parameter-sets=<parameter example, parameter sets in sprop-parameter-sets=<parameter sets
sets data#2> must be associated with level 1b. data#2> must be associated with Level 1b.
Offer SDP: Offer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A00B; //Baseline profile, Level 1.1 a=fmtp:98 profile-level-id=42A00B; //Baseline profile, Level 1.1
packetization-mode=1; packetization-mode=1;
sprop-parameter-sets=<parameter sets data#0>; sprop-parameter-sets=<parameter sets data#0>;
sprop-level-parameter-sets=<parameter sets data#1> sprop-level-parameter-sets=<parameter sets data#1>
Answer SDP: Answer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42B00B; //Baseline profile, Level 1b a=fmtp:98 profile-level-id=42B00B; //Baseline profile, Level 1b
packetization-mode=1; packetization-mode=1;
sprop-parameter-sets=<parameter sets data#2>; sprop-parameter-sets=<parameter sets data#2>;
use-level-src-parameter-sets=1 use-level-src-parameter-sets=1
In the following example, the offer (Baseline profile, level 1.1) In the following example, the offer (Baseline profile, Level 1.1) is
is accepted with level downgrading (the accepted level is 1b), and accepted with level downgrading (the accepted level is Level 1b), and
both "sprop-parameter-sets" and "sprop-level-parameter-sets" are both sprop-parameter-sets and sprop-level-parameter-sets are present
present in the offer. However, the answerer is a legacy RFC 3984 in the offer. However, the answerer is a legacy RFC 3984
implementation and does not understand "sprop-level-parameter-sets", implementation and does not understand sprop-level-parameter-sets;
hence it does not include "use-level-src-parameter-sets" (which the hence, it does not include use-level-src-parameter-sets (which the
answerer does not understand, either) in the answer. Therefore, answerer does not understand either) in the answer. Therefore, the
the answerer must ignore both sprop-parameter-sets=<parameter sets answerer must ignore both sprop-parameter-sets=<parameter sets
data#0> and sprop-level-parameter-sets=<parameter sets data#1>, and data#0> and sprop-level-parameter-sets=<parameter sets data#1>, and
the offerer must transport parameter sets in-band. the offerer must transport parameter sets in-band.
Offer SDP: Offer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A00B; //Baseline profile, Level 1.1 a=fmtp:98 profile-level-id=42A00B; //Baseline profile, Level 1.1
packetization-mode=1; packetization-mode=1;
sprop-parameter-sets=<parameter sets data#0>; sprop-parameter-sets=<parameter sets data#0>;
sprop-level-parameter-sets=<parameter sets data#1> sprop-level-parameter-sets=<parameter sets data#1>
Answer SDP: Answer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42B00B; //Baseline profile, Level 1b a=fmtp:98 profile-level-id=42B00B; //Baseline profile, Level 1b
packetization-mode=1 packetization-mode=1
In the following example, the offer is accepted without level In the following example, the offer is accepted without level
downgrading, and "sprop-parameter-sets" is present in the offer. downgrading, and sprop-parameter-sets is present in the offer.
Parameter sets in sprop-parameter-sets=<parameter sets data#0> must Parameter sets in sprop-parameter-sets=<parameter sets data#0> must
be stored and used used by the encoder of the offerer and the be stored and used by the encoder of the offerer and the decoder of
decoder of the answerer, and parameter sets in sprop-parameter- the answerer, and parameter sets in sprop-parameter-sets=<parameter
sets=<parameter sets data#1>must be used by the encoder of the sets data#1> must be used by the encoder of the answerer and the
answerer and the decoder of the offerer. Note that sprop- decoder of the offerer. Note that sprop-parameter-sets=<parameter
parameter-sets=<parameter sets data#0> is basically independent of sets data#0> is basically independent of sprop-parameter-
sprop-parameter-sets=<parameter sets data#1>. sets=<parameter sets data#1>.
Offer SDP: Offer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0
packetization-mode=1; packetization-mode=1;
sprop-parameter-sets=<parameter sets data#0> sprop-parameter-sets=<parameter sets data#0>
Answer SDP: Answer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0
packetization-mode=1; packetization-mode=1;
sprop-parameter-sets=<parameter sets data#1> sprop-parameter-sets=<parameter sets data#1>
In the following example, the offer is accepted without level In the following example, the offer is accepted without level
downgrading, and neither "sprop-parameter-sets" nor "sprop-level- downgrading, and neither sprop-parameter-sets nor sprop-level-
parameter-sets" is present in the offer, meaning that there is no parameter-sets is present in the offer, meaning that there is no out-
out-of-band transmission of parameter sets, which then have to be of-band transmission of parameter sets, which then have to be
transported in-band. transported in-band.
Offer SDP: Offer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0
packetization-mode=1 packetization-mode=1
Answer SDP: Answer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0
packetization-mode=1 packetization-mode=1
In the following example, the offer is accepted with level In the following example, the offer is accepted with level
downgrading and "sprop-parameter-sets" is present in the offer. As downgrading and sprop-parameter-sets is present in the offer. As
sprop-parameter-sets=<parameter sets data#0> contains level_idc sprop-parameter-sets=<parameter sets data#0> contains level_idc
indicating Level 3.0, therefore cannot be used as the answerer indicating Level 3.0, it therefore cannot be used, as the answerer
wants Level 2.0 and must be ignored by the answerer, and in-band wants Level 2.0, and must be ignored by the answerer, and in-band
parameter sets must be used. parameter sets must be used.
Offer SDP: Offer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0
packetization-mode=1; packetization-mode=1;
sprop-parameter-sets=<parameter sets data#0> sprop-parameter-sets=<parameter sets data#0>
Answer SDP: Answer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A014; //Baseline profile, Level 2.0 a=fmtp:98 profile-level-id=42A014; //Baseline profile, Level 2.0
packetization-mode=1 packetization-mode=1
In the following example, the offer is also accepted with level In the following example, the offer is also accepted with level
downgrading, and neither "sprop-parameter-sets" nor "sprop-level- downgrading, and neither sprop-parameter-sets nor sprop-level-
parameter-sets" is present in the offer, meaning that there is no parameter-sets is present in the offer, meaning that there is no out-
out-of-band transmission of parameter sets, which then have to be of-band transmission of parameter sets, which then have to be
transported in-band. transported in-band.
Offer SDP: Offer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0
packetization-mode=1 packetization-mode=1
Answer SDP: Answer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A014; //Baseline profile, Level 2.0 a=fmtp:98 profile-level-id=42A014; //Baseline profile, Level 2.0
packetization-mode=1 packetization-mode=1
In the following example, the offer is accepted with level In the following example, the offer is accepted with level upgrading,
upgrading, and neither "sprop-parameter-sets" nor "sprop-level- and neither sprop-parameter-sets nor sprop-level-parameter-sets is
parameter-sets" is present in the offer or the answer, meaning that present in the offer or the answer, meaning that there is no out-of-
there is no out-of-band transmission of parameter sets, which then band transmission of parameter sets, which then have to be
have to be transported in-band. The level to use in the offerer- transported in-band. The level to use in the offerer-to-answerer
to-answerer direction is Level 3.0, and the level to use in the direction is Level 3.0, and the level to use in the answerer-to-
answerer-to-offerer direction is Level 2.0. The answerer is offerer direction is Level 2.0. The answerer is allowed to send at
allowed to send at any level up to and including level 2.0, and the any level up to and including Level 2.0, and the offerer is allowed
offerer is allowed to send at any level up to and including level to send at any level up to and including Level 3.0.
3.0.
Offer SDP: Offer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A014; //Baseline profile, Level 2.0 a=fmtp:98 profile-level-id=42A014; //Baseline profile, Level 2.0
packetization-mode=1; level-asymmetry-allowed=1 packetization-mode=1; level-asymmetry-allowed=1
Answer SDP: Answer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0
packetization-mode=1; level-asymmetry-allowed=1 packetization-mode=1; level-asymmetry-allowed=1
In the following example, the offerer is a Multipoint Control Unit In the following example, the offerer is a Multipoint Control Unit
(MCU) in a Topo-Video-switch-MCU like topology [29], offering (MCU) in a topology like Topo-Video-switch-MCU [29], offering
parameter sets received (using out-of-band transport) from three parameter sets received (using out-of-band transport) from three
other participants B, C, and D, and receiving parameter sets from other participants (B, C, and D) and receiving parameter sets from
the participant A, which is the answerer. The participants are the participant A, which is the answerer. The participants are
identified by their values of CNAME, which are mapped to different identified by their values of canonical name (CNAME), which are
SSRC values. The same codec configuration is used by all the four mapped to different SSRC values. The same codec configuration is
participants. The participant A stores and associates the used by all four participants. The participant A stores and
parameter sets included in <parameter sets data#B>, <parameter sets associates the parameter sets included in <parameter sets data#B>,
data#C>, and <parameter sets data#D> to participants B, C, and D, <parameter sets data#C>, and <parameter sets data#D> to participants
respectively, and uses <parameter sets data#B> for decoding NAL B, C, and D, respectively, and uses <parameter sets data#B> for
units carried in RTP packets originated from participant B only, decoding NAL units carried in RTP packets originating from
uses <parameter sets data#C> for decoding NAL units carried in RTP participant B only, uses <parameter sets data#C> for decoding NAL
packets originated from participant C only, and uses <parameter units carried in RTP packets originating from participant C only, and
sets data#D> for decoding NAL units carried in RTP packets uses <parameter sets data#D> for decoding NAL units carried in RTP
originated from participant D only. packets originating from participant D only.
Offer SDP: Offer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=ssrc:SSRC-B cname:CNAME-B a=ssrc:SSRC-B cname:CNAME-B
a=ssrc:SSRC-C cname:CNAME-C a=ssrc:SSRC-C cname:CNAME-C
a=ssrc:SSRC-D cname:CNAME-D a=ssrc:SSRC-D cname:CNAME-D
a=ssrc:SSRC-B fmtp:98 a=ssrc:SSRC-B fmtp:98
sprop-parameter-sets=<parameter sets data#B> sprop-parameter-sets=<parameter sets data#B>
a=ssrc:SSRC-C fmtp:98 a=ssrc:SSRC-C fmtp:98
skipping to change at page 77, line 21 skipping to change at page 75, line 31
Answer SDP: Answer SDP:
m=video 49170 RTP/AVP 98 m=video 49170 RTP/AVP 98
a=ssrc:SSRC-A cname:CNAME-A a=ssrc:SSRC-A cname:CNAME-A
a=ssrc:SSRC-A fmtp:98 a=ssrc:SSRC-A fmtp:98
sprop-parameter-sets=<parameter sets data#A> sprop-parameter-sets=<parameter sets data#A>
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0
packetization-mode=1 packetization-mode=1
8.4. Parameter Set Considerations 8.4. Parameter Set Considerations
The H.264 parameter sets are a fundamental part of the video codec The H.264 parameter sets are a fundamental part of the video codec
and vital to its operation; see section 1.2. Due to their and vital to its operation (see Section 1.2). Due to their
characteristics and their importance for the decoding process, lost characteristics and their importance for the decoding process, lost
or erroneously transmitted parameter sets can hardly be concealed or erroneously transmitted parameter sets can hardly be concealed
locally at the receiver. A reference to a corrupt parameter set locally at the receiver. A reference to a corrupt parameter set
has normally fatal results to the decoding process. Corruption normally has fatal results to the decoding process. Corruption could
could occur, for example, due to the erroneous transmission or loss occur, for example, due to the erroneous transmission or loss of a
of a parameter set NAL unit, but also due to the untimely parameter set NAL unit but also due to the untimely transmission of a
transmission of a parameter set update. A parameter set update parameter set update. A parameter set update refers to a change of
refers to a change of at least one parameter in a picture parameter at least one parameter in a picture parameter set or sequence
set or sequence parameter set for which the picture parameter set parameter set for which the picture parameter set or sequence
or sequence parameter set identifier remains unchanged. Therefore, parameter set identifier remains unchanged. Therefore, the following
the following recommendations are provided as a guideline for the recommendations are provided as a guideline for the implementer of
implementer of the RTP sender. the RTP sender.
Parameter set NALUs can be transported using three different Parameter set NALUs can be transported using three different
principles: principles:
A. Using a session control protocol (out-of-band) prior to the A. Using a session control protocol (out-of-band) prior to the
actual RTP session. actual RTP session.
B. Using a session control protocol (out-of-band) during an ongoing B. Using a session control protocol (out-of-band) during an ongoing
RTP session. RTP session.
C. Within the RTP packet stream in the payload (in-band) during an C. Within the RTP packet stream in the payload (in-band) during an
ongoing RTP session. ongoing RTP session.
It is recommended to implement principles A and B within a session It is recommended to implement principles A and B within a session
control protocol. SIP and SDP can be used as described in the SDP control protocol. SIP and SDP can be used as described in the SDP
Offer/Answer model and in the previous sections of this memo. Offer/Answer model and in the previous sections of this memo.
Section 8.2.2 includes a detailed discussion on transport of Section 8.2.2 includes a detailed discussion on transport of
parameter sets in-band or out-of-band in SDP Offer/Answer using parameter sets in-band or out-of-band in SDP Offer/Answer using media
media type parameters "sprop-parameter-sets", "sprop-level- type parameters sprop-parameter-sets, sprop-level-parameter-sets,
parameter-sets", "use-level-src-parameter-sets" and "in-band- use-level-src-parameter-sets, and in-band-parameter-sets. This
parameter-sets". This section contains guidelines on how section contains guidelines on how principles A and B should be
principles A and B should be implemented within session control implemented within session control protocols. It is independent of
protocols. It is independent of the particular protocol used. the particular protocol used. Principle C is supported by the RTP
Principle C is supported by the RTP payload format defined in this payload format defined in this specification. There are topologies
specification. There are topologies like Topo-Video-switch-MCU [29] like Topo-Video-switch-MCU [29] for which the use of principle C may
for which the use of principle C may be desirable. be desirable.
If in-band signaling of parameter sets is used, the picture and If in-band signaling of parameter sets is used, the picture and
sequence parameter set NALUs SHOULD be transmitted in the RTP sequence parameter set NALUs SHOULD be transmitted in the RTP payload
payload using a reliable method of delivering of RTP (see below), using a reliable method of delivering of RTP (see below), as a loss
as a loss of a parameter set of either type will likely prevent of a parameter set of either type will likely prevent decoding of a
decoding of a considerable portion of the corresponding RTP packet considerable portion of the corresponding RTP packet stream.
stream.
If in-band signaling of parameter sets is used, the sender SHOULD If in-band signaling of parameter sets is used, the sender SHOULD
take the error characteristics into account and use mechanisms to take the error characteristics into account and use mechanisms to
provide a high probability for delivering the parameter sets provide a high probability for delivering the parameter sets
correctly. Mechanisms that increase the probability for a correct correctly. Mechanisms that increase the probability for a correct
reception include packet repetition, FEC, and retransmission. The reception include packet repetition, FEC, and retransmission. The
use of an unreliable, out-of-band control protocol has similar use of an unreliable, out-of-band control protocol has similar
disadvantages as the in-band signaling (possible loss) and, in disadvantages as the in-band signaling (possible loss) and, in
addition, may also lead to difficulties in the synchronization (see addition, may also lead to difficulties in the synchronization (see
below). Therefore, it is NOT RECOMMENDED. below). Therefore, it is NOT RECOMMENDED.
Parameter sets MAY be added or updated during the lifetime of a Parameter sets MAY be added or updated during the lifetime of a
session using principles B and C. It is required that parameter session using principles B and C. It is required that parameter sets
sets are present at the decoder prior to the NAL units that refer be present at the decoder prior to the NAL units that refer to them.
to them. Updating or adding of parameter sets can result in Update or addition of parameter sets can result in further problems;
further problems, and therefore the following recommendations therefore, the following recommendations should be considered.
should be considered.
- When parameter sets are added or updated, care SHOULD be taken - When parameter sets are added or updated, care SHOULD be taken to
to ensure that any parameter set is delivered prior to its usage. ensure that any parameter set is delivered prior to its usage.
When new parameter sets are added, previously unused parameter When new parameter sets are added, previously unused parameter set
set identifiers are used. It is common that no synchronization identifiers are used. It is common that no synchronization is
is present between out-of-band signaling and in-band traffic. present between out-of-band signaling and in-band traffic. If
If out-of-band signaling is used, it is RECOMMENDED that a out-of-band signaling is used, it is RECOMMENDED that a sender not
sender does not start sending NALUs requiring the added or start sending NALUs requiring the added or updated parameter sets
updated parameter sets prior to acknowledgement of delivery from prior to acknowledgement of delivery from the signaling protocol.
the signaling protocol.
- When parameter sets are updated, the following synchronization - When parameter sets are updated, the following synchronization
issue should be taken into account. When overwriting a issue should be taken into account. When overwriting a parameter
parameter set at the receiver, the sender has to ensure that the set at the receiver, the sender has to ensure that the parameter
parameter set in question is not needed by any NALU present in set in question is not needed by any NALU present in the network
the network or receiver buffers. Otherwise, decoding with a or receiver buffers. Otherwise, decoding with a wrong parameter
wrong parameter set may occur. To lessen this problem, it is set may occur. To lessen this problem, it is RECOMMENDED either
RECOMMENDED either to overwrite only those parameter sets that to overwrite only those parameter sets that have not been used for
have not been used for a sufficiently long time (to ensure that a sufficiently long time (to ensure that all related NALUs have
all related NALUs have been consumed), or to add a new parameter been consumed) or to add a new parameter set instead (which may
set instead (which may have negative consequences for the have negative consequences for the efficiency of the video
efficiency of the video coding). coding).
Informative note: In some topologies like Topo-Video-switch- Informative note: In some topologies like Topo-Video-switch-
MCU [29] the origin of the whole set of parameter sets may MCU [29], the origin of the whole set of parameter sets may
come from multiple sources that may use non-unique parameter come from multiple sources that may use non-unique parameter
sets identifiers. In this case an offer may overwrite an set identifiers. In this case, an offer may overwrite an
existing parameter set if no other mechanism that enables existing parameter set if no other mechanism that enables
uniqueness of the parameter sets in the out-of-band channel uniqueness of the parameter sets in the out-of-band channel
exists. exists.
- In a multiparty session, one participant MUST associate - In a multiparty session, one participant MUST associate parameter
parameter sets coming from different sources with the source sets coming from different sources with the source identification
identification whenever possible, e.g. by conveying out-of-band whenever possible, e.g., by conveying out-of-band transported
transported parameter sets, as different sources typically use parameter sets, as different sources typically use independent
independent parameter set identifier value spaces. parameter set identifier value spaces.
- Adding or modifying parameter sets by using both principles B - Adding or modifying parameter sets by using both principles B and
and C in the same RTP session may lead to inconsistencies of the C in the same RTP session may lead to inconsistencies of the
parameter sets because of the lack of synchronization between parameter sets because of the lack of synchronization between the
the control and the RTP channel. Therefore, principles B and C control and the RTP channel. Therefore, principles B and C MUST
MUST NOT both be used in the same session unless sufficient NOT both be used in the same session unless sufficient
synchronization can be provided. synchronization can be provided.
In some scenarios (e.g., when only the subset of this payload In some scenarios (e.g., when only the subset of this payload format
format specification corresponding to H.241 is used) or topologies, specification corresponding to H.241 is used) or topologies, it is
it is not possible to employ out-of-band parameter set transmission. not possible to employ out-of-band parameter set transmission. In
this case, parameter sets have to be transmitted in-band. Here, the
synchronization with the non-parameter-set-data in the bitstream is
implicit, but the possibility of a loss has to be taken into account.
In this case, parameter sets have to be transmitted in-band. Here, The loss probability should be reduced using the mechanisms discussed
the synchronization with the non-parameter-set-data in the above. In case a loss of a parameter set is detected, recovery may
bitstream is implicit, but the possibility of a loss has to be be achieved using a Decoder Refresh Point procedure, for example,
taken into account. The loss probability should be reduced using using RTCP feedback Full Intra Request (FIR) [30]. Two example
the mechanisms discussed above. In case a loss of a parameter set Decoder Refresh Point procedures are provided in the informative
is detected, recovery may be achieved by using a Decoder Refresh Section 8.5.
Point procedure, for example, using RTCP feedback Full Intra
Request (FIR) [30]. Two example Decoder Refresh Point procedures
are provided in the informative Section 8.5.
- When parameter sets are initially provided using principle A and - When parameter sets are initially provided using principle A and
then later added or updated in-band (principle C), there is a then later added or updated in-band (principle C), there is a risk
risk associated with updating the parameter sets delivered out- associated with updating the parameter sets delivered out-of-band.
of-band. If receivers miss some in-band updates (for example, If receivers miss some in-band updates (for example, because of a
because of a loss or a late tune-in), those receivers attempt to loss or a late tune-in), those receivers attempt to decode the
decode the bitstream using out-dated parameters. It is bitstream using outdated parameters. It is therefore RECOMMENDED
therefore RECOMMENDED that parameter set IDs be partitioned that parameter set IDs be partitioned between the out-of-band and
between the out-of-band and in-band parameter sets. in-band parameter sets.
8.5. Decoder Refresh Point Procedure using In-Band Transport of 8.5. Decoder Refresh Point Procedure Using In-Band Transport of
Parameter Sets (Informative) Parameter Sets (Informative)
When a sender with a video encoder according to [1] receives a When a sender with a video encoder according to [1] receives a
request for a decoder refresh point, the encoder shall enter the request for a decoder refresh point, the encoder shall enter the fast
fast update mode by using one of the procedures specified update mode by using one of the procedures specified in Sections
in Section 8.5.1 or 8.5.2 below. The procedure in 8.5.1 is the 8.5.1 or 8.5.2. The procedure in Section 8.5.1 is the preferred
preferred response in a lossless transmission environment. Both response in a lossless transmission environment. Both procedures
procedures satisfy the requirement to enter the fast update mode satisfy the requirement to enter the fast update mode for H.264 video
for H.264 video encoding. encoding.
8.5.1. IDR Procedure to Respond to a Request for a Decoder Refresh 8.5.1. IDR Procedure to Respond to a Request for a Decoder Refresh
Point Point
This section gives one possible way to respond to a request for a This section gives one possible way to respond to a request for a
decoder refresh point. decoder refresh point.
The encoder shall, in the order presented here: The encoder shall, in the order presented here:
1) Immediately prepare to send an IDR picture. 1) Immediately prepare to send an IDR picture.
2) Send a sequence parameter set to be used by the IDR picture to 2) Send a sequence parameter set to be used by the IDR picture to be
be sent. The encoder may optionally also send other sequence sent. The encoder may optionally also send other sequence
parameter sets. parameter sets.
3) Send a picture parameter set to be used by the IDR picture to be 3) Send a picture parameter set to be used by the IDR picture to be
sent. The encoder may optionally also send other picture sent. The encoder may optionally also send other picture
parameter sets. parameter sets.
4) Send the IDR picture. 4) Send the IDR picture.
5) From this point forward in time, send any other sequence or 5) From this point forward in time, send any other sequence or
picture parameter sets that have not yet been sent in this picture parameter sets that have not yet been sent in this
procedure, prior to their reference by any NAL unit, regardless procedure, prior to their reference by any NAL unit, regardless of
of whether such parameter sets were previously sent prior to whether such parameter sets were previously sent prior to
receiving the request for a decoder refresh point. As needed, receiving the request for a decoder refresh point. As needed,
such parameter sets may be sent in a batch, one at a time, or in such parameter sets may be sent in a batch, one at a time, or in
any combination of these two methods. Parameter sets may be re- any combination of these two methods. Parameter sets may be
sent at any time for redundancy. Caution should be taken when re-sent at any time for redundancy. Caution should be taken when
parameter set updates are present, as described above in Section parameter set updates are present, as described above in Section
8.4. 8.4.
8.5.2. Gradual Recovery Procedure to Respond to a Request for a 8.5.2. Gradual Recovery Procedure to Respond to a Request for a Decoder
Decoder Refresh Point Refresh Point
This section gives another possible way to respond to a request for This section gives another possible way to respond to a request for a
a decoder refresh point. decoder refresh point.
The encoder shall, in the order presented here: The encoder shall, in the order presented here:
1) Send a recovery point SEI message (see Sections D.1.7 and D.2.7 1) Send a recovery point SEI message (see Sections D.1.7 and D.2.7 of
of [1]). [1]).
2) Repeat any sequence and picture parameter sets that were sent 2) Repeat any sequence and picture parameter sets that were sent
before the recovery point SEI message, prior to their reference before the recovery point SEI message, prior to their reference by
by a NAL unit. a NAL unit.
The encoder shall ensure that the decoder has access to all The encoder shall ensure that the decoder has access to all reference
reference pictures for inter prediction of pictures at or after the pictures for inter prediction of pictures at or after the recovery
recovery point, which is indicated by the recovery point SEI point, which is indicated by the recovery point SEI message, in
message, in output order, assuming that the transmission from now output order, assuming that the transmission from now on is error-
on is error-free. free.
The value of the recovery_frame_cnt syntax element in the recovery The value of the recovery_frame_cnt syntax element in the recovery
point SEI message should be small enough to ensure a fast recovery. point SEI message should be small enough to ensure a fast recovery.
As needed, such parameter sets may be re-sent in a batch, one at a As needed, such parameter sets may be re-sent in a batch, one at a
time, or in any combination of these two methods. Parameter sets time, or in any combination of these two methods. Parameter sets may
may be re-sent at any time for redundancy. Caution should be taken be re-sent at any time for redundancy. Caution should be taken when
when parameter set updates are present, as described above in parameter set updates are present, as described above in Section 8.4.
Section 8.4.
9. Security Considerations 9. Security Considerations
RTP packets using the payload format defined in this specification RTP packets using the payload format defined in this specification
are subject to the security considerations discussed in the RTP are subject to the security considerations discussed in the RTP
specification [5], and in any appropriate RTP profile (for example, specification [5] and in any appropriate RTP profile (for example,
[16]). This implies that confidentiality of the media streams is [16]). This implies that confidentiality of the media streams is
achieved by encryption; for example, through the application of achieved by encryption, for example, through the application of SRTP
SRTP [26]. Because the data compression used with this payload [26]. Because the data compression used with this payload format is
format is applied end-to-end, any encryption needs to be performed applied end-to-end, any encryption needs to be performed after
after compression. A potential denial-of-service threat exists for compression. A potential denial-of-service threat exists for data
data encodings using compression techniques that have non-uniform encodings using compression techniques that have non-uniform
receiver-end computational load. The attacker can inject receiver-end computational load. The attacker can inject
pathological datagrams into the stream that are complex to decode pathological datagrams into the stream that are complex to decode and
and that cause the receiver to be overloaded. H.264 is that cause the receiver to be overloaded. H.264 is particularly
particularly vulnerable to such attacks, as it is extremely simple vulnerable to such attacks, as it is extremely simple to generate
to generate datagrams containing NAL units that affect the decoding datagrams containing NAL units that affect the decoding process of
process of many future NAL units. Therefore, the usage of data many future NAL units. Therefore, the usage of data origin
origin authentication and data integrity protection of at least the authentication and data integrity protection of at least the RTP
RTP packet is