Internet Engineering Task Force                 Yoshihiro Kikuchi - Toshiba
Internet Draft                                       Toshiyuki Nomura - NEC
Document: draft-ietf-avt-rtp-mpeg4-es-00.txt draft-ietf-avt-rtp-mpeg4-es-01.txt         Shigeru Fukunaga - Oki
                                              Yoshinori Matsui - Matsushita
                                                       Hideaki Kimata - NTT
                                                           February 1,
                                                               May 31, 2000

             RTP payload format for MPEG-4 Audio/Visual streams

Status of this Memo

   This document is an Internet-Draft and is in full conformance with all
      provisions of Section 10 of RFC2026 [1].

   Internet-Drafts are working documents of the Internet Engineering Task
   Force (IETF), its areas, and its working groups. Note that other groups
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   are draft documents valid for a maximum of six months and may be updated,
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   inappropriate to use Internet- Drafts as reference material or to cite
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   http://www.ietf.org/ietf/1id-abstracts.txt
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   http://www.ietf.org/shadow.html.

                                   Abstract

   This document describes RTP payload formats for the carriage of MPEG-4
   Audio and Visual streams[2][3], and an RTCP format for MPEG-4 upstream
   messages functionalities[4]. In this specification, MPEG-4 Audio/Visual
   bitstreams are directly mapped into RTP packets without using MPEG-4
   Systems[6]. packets. The RTP header fields
   usage and the fragmentation rule for MPEG-4 Visual and Audio bitstreams
   are specified. It also specifies an RTCP packet usage to carry the MPEG-4
   upstream messages. In addition, MIME type registrations and SDP usages
   for the MPEG-4 Audio and Visual streams are defined in this document.

1. Introduction

1.1 Why MPEG-4 Audio/Visual RTP format needed?

   The RTP payload formats described in this Internet-Draft specify the
   normative a way on of
   how MPEG-4 Audio/Visual Audio and Visual streams are fragmented and mapped directly
   onto RTP packets. No extra header field is used for such
   functionality as error protection or grouping of streams.

   H.323 terminals could be the case. an example where such RTP payload formats are
   used.  MPEG-4 Audio/Visual streams are not managed by Object Descriptors[6] Descriptors
   of MPEG-4 Systems[6] but H.245, and by H.245. The streams are directly mapped into onto
   RTP packets without Sync Layer[6]. using the synchronization functionality of MPEG-4
   Systems [6].

   The semantics of RTP headers in this case such cases need to be clearly defined defined,
   including the association with the MPEG-4 Audio/Visual data elements.  In
   addition, it would be beneficial to define the fragmentation rule of RTP
   packets for MPEG-4 Video streams so as to enhance error resiliency by
   utilizing the error resilience tools provided inside the MPEG-4 Video
   stream.  However, they have these items are not been studied
   until now. covered by other RTP payload format
   proposals.

1.2 Consideration on the MPEG-4 Visual RTP payload format

   MPEG-4 Visual is a visual coding standard with many new functionalities:
   high coding efficiency, high error resiliency, multiple arbitrary shaped
   object based coding, etc. [2]. It covers a wide range of bitrate from
   several Kbps to many Mbps. It also covers a wide variety of networks
   ranging from guarantied with to be almost error-free to mobile networks with
   high error rate by due to its error resilience functionalities.

   A normative way of fragmentation of rule for an MPEG-4 visual bitstream into RTP packets is
   defined in this Internet draft. document. Since MPEG-4 Visual is used for a wide variety
   of networks, it is desirable not desired to apply too much restriction on to the
   fragmentation.  A fragmentation rule like a "a single video packet shall
   always be mapped on a single RTP packet. packet" may be inappropriate. On the
   other hand, a careless media unaware fragmentation may cause degradation
   of the error resiliency and the bandwidth efficiency. The fragmentation
   rule described in this
   Internet draft document is flexible but to define the minimum
   rules to prevent and guidelines for preventing the meaningless fragmentation and to
   utilizing the error resilience functionality of e.g. splitting a header into packets. MPEG-4 visual.

   For video coding media such as H.261 or MPEG-1/2, the additional media
   specific RTP header works effectively for recovering e.g. recovering. e.g., of a picture
   header corrupt corrupted by packet losses. However, there are error resilience
   functionalities inside MPEG-4 Visual to recover corrupt headers. These
   functionalities can commonly be used on RTP/IP network as well as other
   networks. (H.223/mobile, MPEG-2/TS, etc.) Therefore, no extra RTP header
   fields are defined in the MPEG-4 Visual RTP payload format.

1.3 Consideration on the MPEG-4 Audio RTP payload format

   MPEG-4 Audio is a new kind of audio standard that integrates many
   different types of audio coding tools. It also supports a mechanism
   representing synthesized sounds. Low-overhead MPEG-4 Audio Transport
   Multiplex (LATM) manages the sequence of the compressed or the
   represented audio data by MPEG-4 Audio tools with relatively small
   overhead. In audio-only applications, the LATM-based MPEG-4 Audio
   bitstreams, therefore, are desirable to be directly mapped into the RTP
   packets without using MPEG-4 Systems.

   Furthermore, if the payload of a packet is a single audio frame, a packet
   loss does not impair the decodability of adjacent packets. Therefore, a
   payload specific header for MPEG-4 Audio is not required as same as one
   for the other audio coders.

1.4 MPEG-4 Audio/Visual upstream messaging on RTCP packets

   In some cases,

   Some particular tools of MPEG-4 Audio/Visual has support upstream messaging
   functionalities. These messages are extremely Audio/Visual specific,
   since coders directly use these messages for controlling coding
   parameters. From the point of view of controlling parameters, these
   messages should be transmitted without delay. Therefore Therefore, these messages
   are directly mapped onto some kind of low delay RTCP packets. The use of
   this type of RTCP packets is limited to the case when the MPEG-4 upstream
   functionalities in some particular profiles are used (e.g. MPEG-4 Visual
   Advanced Real Time Simple Profile, NEWPRED tool).

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [7].

3. RTP Packetization of MPEG-4 Visual bitstream

   This section specifies the RTP packetization rule for MPEG-4 Visual
   content. An MPEG-4 Visual bitstream is mapped directly onto the RTP
   payload without any addition of extra header fields or removal of any
   Visual syntax elements. The Combined Configuration/Elementary streams
   mode is used so that the configuration information is carried in the same
   RTP port as the elementary stream. (see 6.2.1 "Start codes" of ISO/IEC
   14496-2 [2][9][4])
   When the short video header mode is used, RTP payload format for H.263
   specified in the relevant RFCs or other standards MAY be used.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |V=2|P|X|  CC   |M|     PT      |       sequence number         | RTP
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           timestamp                           | Header
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           synchronization source (SSRC) identifier            |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |            contributing source (CSRC) identifiers             |
   |                             ....                              |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |                                                               | RTP
   |       MPEG-4 Visual stream (byte aligned)                     | Payload
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :...OPTIONAL RTP padding        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 1 - An RTP packet for MPEG-4 Visual stream

3.1 RTP header fields usage for MPEG-4 Visual

   Payload Type (PT): Distinct payload type should be assigned to specify
   MPEG-4 Visual RTP payload format. If the dynamic payload type assignment
   is used, it is specified by some out-of-band means (e.g. H.245, SDP,
   etc.) that the MPEG-4 Visual payload format is used for the corresponding
   RTP packet.

   Extension (X) bit: Defined by the RTP profile used.

   Sequence Number: Increment by one for each RTP data packet sent. It
   starts with a random initial value for security reasons.

   Marker (M) bit: The marker bit is set to one to indicate the last RTP
   packet (or only RTP packet) of a VOP.

   Timestamp: The timestamp indicates the composition time, or the
   presentation time in a no-compositor decoder by adding a constant random
   offset for security reasons. For a video object plane, it is defined by
   vop_time_increment (in units of 1/vop_time_increment_resolution seconds)
   plus the cumulative number of whole seconds specified by module_time_base
   and time_code of Group_of_VideoObjectPlane() if present. In the case of
   interlaced video, a VOP consists of lines from two fields and the
   timestamp indicates the composition time of the first field. If the RTP
   packet contains only configuration information and/or
   Group_of_VideoObjectPlane(), the composition time of the subsequent VOP
   in the coding order is used. If the RTP packet contains only
   visual_object_sequence_end_code, the composition time of the immediately
   preceding VOP in the coding order is used.

   Unless specified by an out-of-band means, means (e.g. SDP parameter or MIME
   parameter as defined in section 6), the resolution of the timestamp is
   set to its default (90KHz).

   SSRC, CC and CSRC fields are used as described in RFC 1889 [8].

3.2 Fragmentation of MPEG-4 Visual bitstream

   A fragmented MPEG-4 Visual bitstream is mapped directly onto the RTP
   payload without any addition of extra header fields or removal of any
   Visual syntax elements. The Combined Configuration/Elementary streams
   mode is used. The following rules apply for the fragmentation.

   (1) The configuration information and Group_of_VideoObjectPlane() SHALL
   be placed at the beginning of the RTP payload (just after the RTP header)
   or just after the header of the syntactically upper layer function.

   (2) If one or more headers exist in the RTP payload, the RTP payload
   SHALL begin with the header of the syntactically highest function.
   Note: The visual_object_sequence_end_code is regarded as the lowest
   function.

   (3) A header SHALL NOT be split into a plurality of RTP packets.

   (4) Two or more VOPs SHALL be fragmented into different RTP packets so
   that one RTP packet consists of the data bytes associated with an unique
   presentation time (that indicated to the timestamp field in the RTP
   packet header).

   (5) A single video packet SHOULD NOT be split into a plurality of RTP
   packets. The size of a video packet SHOULD be adjusted such that the
   resulting RTP packet is not larger than the path-MTU.

   Hear, A video packet MAY
   be split into a plurality of RTP packets when the size of the video
   packet is large.

   Here, header means:
   - Configuration information (Visual Object Sequence Header, Visual Object
     Header and Visual Video Object Layer Header)
   - visual_object_sequence_end_code
   - The header of the entry point function for an elementary stream
     (Group_of_VideoObjectPlane() or the header of VideoObjectPlane(),
     video_plane_with_short_header(), MeshObject() or FaceObject())
   - The video packet header (video_packet_header() excluding
     next_resync_marker())
   - The header of gob_layer()
   See 6.2.1 "Start codes" of ISO/IEC 14496-2[2][9][4] for the definition of
   the configuration information and the entry point functions.

   The video packet starts with the VOP header or the video packet header,
   followed by motion_shape_texture(), and ends with next_resync_marker() or
   next_start_code).

3.3 Examples of packetized MPEG-4 Visual bitstream

   Considering that MPEG-4 Visual is used on a wide variety of networks from
   several Kbps to many Mbps, from guarantied guaranteed networks with which are almost error-
   free
   error-free to mobile networks with high error rate, it is desirable not desired
   to apply too much restriction on to the fragmentation like a single video packet
   shall always be mapped on a single RTP packet. fragmentation. On the other hand, a
   careless media unaware fragmentation will cause degradation of the error
   resiliency and the bandwidth efficiency. The fragmentation criteria
   described in 3.2 are flexible but to define the minimum rules to prevent
   the
   meaningless fragmentation of e.g. splitting a header into packets. fragmentation.

   For video coding media such as H.261 or MPEG-1/2, the additional media
   specific RTP header works effectively for recovering e.g. recovering, e.g., of a picture
   header corrupt corrupted by packet losses. However, there is an error resilience
   functionality inside MPEG-4 Visual to recover corrupt headers. This
   functionality can commonly be used on RTP/IP network as well as other
   networks. (H.223/mobile, MPEG-2/TS, etc.) Therefore, there is no strong
   reason to define MPEG-4 Visual specific extra RTP header fields.

   Figure 2 shows examples of RTP packets generated based on the criteria
   described in 3.2

   (a) is an example of the first RTP packet or the random access point of
   an MPEG-4 visual bitstream. This RTP packet contains the configuration
   information. According to the criterion (1), the Visual Object Sequence
   Header(VS header) is placed at the beginning of the RTP payload, and the
   Visual Object Header and the Visual Video Object Layer Header(VO header, VOL
   header) follow it. Since the fragmentation rule defined in 3.2 guaranties guarantees
   that the configuration information, starting with
   visual_object_sequence_start_code, is always placed at the beginning of
   the RTP payload, RTP receivers can detect the random access point by
   checking if the first 32-bit field of the RTP payload is
   visual_object_sequence_start_code.

   (b) is an another example of the RTP packet that contains
   Group_of_VideoObjectPlane(GOV). Following containing the criterion (1), configuration
   information. The difference from the GOV example (a) is
   placed at that this RTP packet
   also contains a video packet in the VOP following the configuration
   information. Since the length of the configuration information is
   relatively short (typically several ten bytes), an RTP packet containing
   only the configuration information may increase the overhead. Therefore,
   the configuration information and the immediately following GOV and/or (a
   part of) VOP can be packetized into a single RTP packet like this
   example.

   (c) is an example the RTP packet that contains
   Group_of_VideoObjectPlane(GOV). Following the criterion (1), the GOV is
   placed at the beginning of the RTP payload. It is a waste of RTP/IP
   header overhead to generate a RTP packet containing only a GOV whose
   length is 7 bytes. Therefore, (a part of) the following VOP can be placed
   in the same RTP packet as shown in (b).

   (c) (c).

   (d) is an example that of the case where one video packet is packetized into
   one RTP packet. When the packet-loss rate of the underlying network is
   high, this kind of packetization is recommended. It is strongly
   recommended to set resync_marker_disable to 0 in the VOL header to enable
   adjustment of the video packet size. Even when the RTP packet containing
   the VOP header is discarded by a packet loss, the other RTP packets can
   be decoded by using the HEC(Header Extension Code) information in the
   video packet header. No extra RTP header field is necessary.

   (d)

   (e) is an example that of the case where more than one video packets are
   packetized into one RTP packet. This kind of packetization is effective
   to save the overhead of RTP/IP headers if the bit-rate of the underlying
   network is low. However, it will decrease the packet-loss resiliency
   because multiple video packets are discarded by a single RTP packet loss.
   The adequate number of video packets in a RTP packet and the RTP packet
   length depend the packet-loss rate and the bit-rate of the underlying
   network.

   Figure 3 shows examples of RTP packets prohibited by the criteria of 3.2.

   Fragmentation of a header into multiple RTP packets, like (a), will not
   only increase the overhead of RTP/IP headers but also decrease the error
   resiliency. Therefore, it is prohibited by the criterion (3).

   When concatenating more than one video packets into a an RTP packet, VOP
   header or video_packet_header() shall not be placed in the middle of the
   RTP payload. The packetization like (b) is not allowed by the criterion
   (2). This is because of the error resiliency. Comparing this example with
   Figure 2(c), two video packets are mapped onto two RTP packets in both
   cases. However, there is a difference between the packet-loss resiliency.
   When the second RTP packet is lost, both video packets 1 and 2 are lost
   in the case of Figure 3(b) whereas only video packet 2 is lost in the
   case of Figure 2(c).

   A

   An RTP packet containing more than one VOPs, like (c), is not allowed.

       +------+------+------+------+
   (a) | RTP  |  VS  |  VO  | VOL  |
       |header|header|header|header|
       +------+------+------+------+

       +------+-----+------------------+

       +------+------+------+------+------------+
   (b) | RTP  |  VS  |  VO  | VOL  |Video Packet|
       |header|header|header|header|            |
       +------+------+------+------+------------+

       +------+-----+------------------+
   (c) | RTP  | GOV |Video Object Plane|
       |header|     |                  |
       +------+-----+------------------+

       +------+------+------------+  +------+------+------------+
   (c)
   (d) | RTP  | VOP  |Video Packet|  | RTP  |  VP  |Video Packet|
       |header|header|    (1)     |  |header|header|    (2)     |
       +------+------+------------+  +------+------+------------+

       +------+------+------------+------+------------+------+------------+
   (d)
   (e) | RTP  |  VP  |Video Packet|  VP  |Video Packet|  VP  |Video Packet|
       |header|header|     (1)    |header|    (2)     |header|    (3)     |
       +------+------+------------+------+------------+------+------------+

        Figure 2 - Examples of RTP packetized MPEG-4 Visual bitstream

       +------+-------------+  +------+------------+------------+
   (a) | RTP  |First half of|  | RTP  |Last half of|Video Packet|
       |header|  VP header  |  |header|  VP header |            |
       +------+-------------+  +------+------------+------------+

       +------+------+----------+  +------+---------+------+------------+
   (b) | RTP  | VOP  |First half|  | RTP  |Last half|  VP  |Video Packet|
       |header|header| of VP(1) |  |header| of VP(1)|header|    (2)     |
       +------+------+----------+  +------+---------+------+------------+

       +------+------+------------------+------+------------------+
   (c) | RTP  | VOP  |Video Object Plane| VOP  |Video Object Plane|
       |header|header|        (1)       |header|       (2)        |
       +------+------+------------------+------+------------------+

   Figure 3 - Examples of prohibited RTP packetization for MPEG-4 Visual
   bitstream

4. RTP Packetization of MPEG-4 Audio bitstream

   When tools defined in MPEG-4 Systems are not used MPEG-4 Audio stream is
   formatted by LATM (Low-overhead MPEG-4 Audio Transport Multiplex)
   format[5], and then mapped onto RTP packets as described the subsequent
   section.

4.1 RTP Packet Format

   The LATM consists of the sequence of audioMuxElements that include one or
   more audio frames. A complete audioMuxElement or the part of
   audioMuxElements SHALL be mapped directly onto the RTP payload without
   removal of any audioMuxElement syntax elements as shown in Figure 4. The
   first byte of each audioMuxElement SHALL be located at the first payload
   location of an RTP packet.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |V=2|P|X|  CC   |M|     PT      |       sequence number         |RTP
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           timestamp                           |Header
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           synchronization source (SSRC) identifier            |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |            contributing source (CSRC) identifiers             |
   |                             ....                              |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |                                                               |RTP
   :                 audioMuxElement (byte aligned)                :Payload
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :...OPTIONAL RTP padding        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 4 - An RTP packet for MPEG-4 Audio

   It is required for the audioMuxElement to indicate the following
   muxConfigPresent information by an out-of-band means.

   muxConfigPresent: If this information is set to 1, the audioMuxElement
   SHALL include an indication bit "useSameStreamMux" and MAY include the
   configuration information for audio compression "StreamMuxConfig". The
   useSameStreamMux bit indicates whether the StreamMuxConfig element in the
   previous frame is applied in the current frame.

4.2 RTP Header Fields Usage

   Payload Type (PT): Distinct payload type should be assigned to specify
   MPEG-4 Audio RTP payload format. If the dynamic payload type assignment
   is used, it is specified by some out-of-band means (e.g. H.245, SDP,
   etc.) that the MPEG-4 Audio payload format is used for the corresponding
   RTP packet.

   Marker (M) bit: The marker bit indicates audioMuxElement boundaries. This
   bit is set to one to mark the RTP packet contains a complete
   audioMuxElement or the last fragment of an audioMuxElement.

   Timestamp: The timestamp indicates the composition time, or the
   presentation time in a no-compositor decoder. Timestamps are recommended
   to start at a random value for security reasons.

   Unless specified by an out-of-band means, the resolution of the timestamp
   is set to its default (90 kHz).

   Sequence Number: Increment by one for each RTP packet sent. It starts
   with a random value for security reasons.

   SSRC, CC and CSRC fields are used as described in RFC 1889 [8].

4.3 Fragmentation of MPEG-4 Audio bitstream

   It is desirable to put one audioMuxElement per RTP packet. The size of an
   audioMuxElement is tried to be adjusted such that the resulting RTP
   packet is not larger than the path-MTU. If this is not possible, the
   audioMuxElement MAY be fragmented across several packets based on the
   following rules.

   (1) "payloadMux" which consists of payload elements MAY be fragmented
   into several RTP packets so that one RTP packet consists of one or more
   payload elements. A payload element SHOULD NOT be fragmented.

   (2) If the audioMuxElement includes StreamMuxConfig, StreamMuxConfig
   SHALL be included into the RTP packet containing the first payload
   element.

5. RTCP Packetization of MPEG-4 upstream messages

   This section specifies the usage of particular RTCP packets to carry the
   upstream messages generated using the MPEG-4 Audio/Visual upstream
   messaging functionalities, e.g. NEWPRED[4]. RTCP packets specified functionalities. In the current specification, NEWPRED in the
   MPEG-4 Visual Advance Real Time Simple (ARTS) Profile[4] is only the tool
   which uses this section RTCP payload specification. This particular RTCP packet
   SHALL ONLY be used when it is indicated by some out of band means that
   the corresponding MPEG-4 Visual codec is compliant with the ARTS profile
   and
   level indication it is indicated in the configuration information of MPEG-4 the codecs have such functionalities. (e.g.
   Advanced Real Time Simple Visual Profile[4])

   The MPEG-4 upstream messages are transmitted on particular RTCP packets,
   like H.261 RTCP control packets [10].

   In the case visual
   bitstream that the RTP session uses a multicast address, the MPEG-4
   upstream message packets are not transmitted NEWPRED tool is enabled (newpred_enable is set to 1).

5.1. Abstract of NEWPRED in the ARTS profile
   NEWPRED in the ARTS profile is an error resilience tool using the normal RTCP
   destination transport address. Instead, these
   upstream message packets
   are sent directly via unicast messages from the decoder to the coder.  The
   destination port number of these upstream message packets encoder.  As the inter-frame
   coding is always same
   to used in the port number of MPEG-4 Visual standard, the normal RTCP address.

   As a consequence, these upstream message packets may only image degradation by
   packet loss will be used when no
   RTP mixers or translators intervene in the path from propagated to the coder after several frames.  In order to
   prevent the
   decoder.  If such intermediate systems do intervene, temporal error propagation, the address reference frames of the
   coder would no longer be present as
   inter-frame coding are switched according to the network-level source address upstream messages in
   packets received by the decoder, and in fact, it might not
   NEWPRED.  As the correct frames are used as the reference frame, the
   error propagation is refreshed.

   As neither the re-transmission nor the intra refresh are used, the coding
   efficiency can be possible
   for kept high.  And the decoder to send packets directly to NEWPRED can achieve the coder.

   Some reliable multicast protocols use similar NACK control packets faster
   error recovery than the intra refresh.

   There are two types of upstream messages; acknowledged message (NP_ACK)
   and non-acknowledged message (NP_NACK).  NP_ACK and/or NP_NACK messages
   are transmitted over on the normal multicast distribution channel, however they
   typically use random delays to prevent a NACK implosion problem. particular RTCP packets in the NEWPRED.  The goal
   selecting methods of such protocols is to provide reliable multicast packet delivery at reference frames are dependent on the
   expense kind of delay, which is appropriate for applications such as a shared
   whiteboard.

   On the other hand, used
   messages.

5.2. Particular RTCP packets keep low delay

   The real-time Audio/Visual transmission is more sensitive to delay and
   does not require full reliability.  For Audio/Visual applications it is
   more effective to send the MPEG-4 upstream message packets as soon as
   possible, i.e. as soon as a loss is detected, without adding any random
   delays.

5.1.  MPEG-4 Visual upstream message packets definition

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |V=2|P|   UMT   | PT=RTCP_MP4UM |           length              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              SSRC                             |
       +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
       |       MPEG-4 Upstream Messages Payload (byte aligned)         |
       |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                               :             padding           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   version (V): 2 bits
        Identifies

5.3.  Congestion control

   In the version cases of RTP, which the demand type of intra refresh or the re-transmission,
   the amount of bits during the congestion is larger than that in the same error
   free terms.  Therefore they may cause some another congestion.  While in RTCP packets
   the NEWPRED, as
       in RTP data packets.

   padding (P): 1 bit
       If the padding bit intra-frame coding is set, this RTCP packet contains some additional
       padding octets at the end which are not part used, the increased amount
   of bits is much lower than that of the control
       information. intra refresh or the re-
   transmission even in the case of packet loss.  Therefore NEWPRED causes
   less additional burden for the congestion.

   The last octet amount of the padding upstream messages is a count dependent on the strategy of how many
       padding octets the
   selecting methods of reference frames of the encoder and that of the
   sending upstream messages of the decoder.  In order to avoid congestion,
   the amount of upstream message packets should be ignored. small. In the case several NEWPRED,
   the decoder can control the amount of them by not sending some upstream
   messages; For example, in the case that the NP_NACK messages are mapped onto one RTCP packet, padding should only be
       required on mainly
   used to select the reference frames in the encoder, the decoder may not
   send the NP_ACK messages even if it receives downstream data.  On the
   other hand, in the case that the NP_ACK messages are mainly used in the
   encoder, the decoder may not send the NP_NACK messages. The amount of the last individual message.
   upstream message type (UMT): 5 bits
       Identifies messages is at most 5% (normally about 1%) of the type visual
   downstream data.

   Especially the amount of NP_ACK messages is decreased in the MPEG-4 case of
   packet loss.  Therefore the NP_ACK message has no additional burden for
   the congestion.  On the other hand, NP_NACK messages corresponding to the
   lost packets are usually sent after the congestion, because the decoder
   detects the packet loss after the next downstream packet reaches.
   Therefore the NP_NACK message has less additional burden for the
   congestion, too.

   And to reduce the number of particular RTCP packets, multiple upstream messages.
       0:       forbidden
       1:       MPEG-4 Visual NEWPRED
       2-63:    reserved
   messages can be concatenated in the payload of one particular RTCP
   packet.  In this internet-draft, only NEWPRED case, it is desirable to send these concatenated
   messages as soon as possible.

   The particular RTCP transmission interval is according to the interval of
   the decoding the visual downstream data.  Both the receiving interval of
   the visual RTP packet and the decoding time for each packet data have
   some jitter for themselves.  Therefore the particular RTCP transmission
   interval has some jitter for itself.  It is effective for the congestion
   control, and there is no need to add any random delays.  This means that
   the size of sending jitter is enough to avoid another congestion only in
   case of the unicast.

5.4. Limiting to Unicast

   The NEWPRED can work in multicast only in the case that the number of
   decoders is small.  However in order to avoid the additional congestion,
   the NEWPRED over RTP/RTCP SHALL NOT be used in multicast.

5.5. Relations with SR and RR
   The particular low delay RTCP packets for the MPEG-4 upstream messages
   SHALL be treated as the completely different kind of packets from the
   normal RTCP packets; such as SR, RR and so on.

   For example, if the particular RTCP packets would be included in the
   calculation of RTCP sending interval, the RR packets should be generated
   in the timing of the particular low delay RTCP packets.  In this case,
   the interval of the RR packets would be smaller than 5 seconds, and the
   number of the normal RTCP packets is much increased. It is bad for the
   congestion.

   Therefore all particular RTCP packets SHALL be ignored to analyze the
   information in the sender and receiver reports (SR and RR), and only
   normal RTCP packets are used.

   Multiple particular RTCP packets can be concatenated without any
   intervening separators to form a compound RTCP packet.  The normal
   compound RTCP packet SHOULD start with SR or RR packets. However in the
   case of compound particular RTCP packet, other normal RTCP packets SHALL
   NOT be included, and only particular RTCP packets SHALL be included in
   one compound particular RTCP packet.

5.6.  MPEG-4 Visual upstream message packets definition
        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |V=2|P|   UMT   | PT=RTCP_MP4U  |           length              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              SSRC                             |
       +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
       |       MPEG-4 Upstream Messages Payload (byte aligned)         |
       |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                               :             padding           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   version (V): 2 bits
        Identifies the version of RTP, which is the same in RTCP packets as
       in RTP data packets.

   padding (P): 1 bit
        If the padding bit is set, this RTCP packet contains some additional
        padding octets at the end which are not part of the control
        information. The last octet of the padding is a count of how many
        padding octets should be ignored. In the case several upstream
        messages are mapped onto one RTCP packet, padding should only be
        required on the last individual message.

   upstream message type (UMT): 5 bits
       Identifies the type of the MPEG-4 upstream messages.
       0:       forbidden
       1:       MPEG-4 Visual NEWPRED in the ARTS Profile
       2-63:    reserved
       In this internet-draft, only the NEWPRED in the ARTS profile is
       assigned as the candidate of the UMT for the moment.  Some other
       MPEG-4 Audio/Visual applications using the upstream messages may be
       assigned in the future.

   packet type (PT): 8 bits
       The value of the packet type (PT) identifier is the constant
       RTCP_MP4U (TBD).

   SSRC: 32 bits
       SSRC is the synchronization source identifier for the sender of this
       packet.

   MPEG-4 Upstream Message Payload: variable
        The syntax and semantics of the MPEG-4 upstream messages are defined
        in the ISO/IEC 14496-2/3[4][5]. All messages are byte aligned.
        Normally one message is mapped onto one RTCP packet, and several
        messages with same UMT could be continuously mapped onto one RTCP
        packet.  One message SHALL NOT be fragmented into different RTCP
        packets.

6. MIME type registration for MPEG-4 Audio/Visual streams

   The following sections describe the MIME type registrations for the MPEG-
   4 Audio/Visual streams. MIME type registration and SDP usage for the
   MPEG-4 Visual stream are described in sections 6.1 and 6.2, respectively.
   MIME type registration and SDP usage for the MPEG-4 Audio stream are
   described in sections 6.3 and 6.4, respectively.

   (In the following sections, the RFC number "XXXX" represents the RFC
   number, which should be assigned for this Internet Draft.)

6.1 MIME type registration for MPEG-4 Visual

   MIME media type name: video

   MIME subtype name: MP4V

   Required parameters: none

   Optional parameters:
     rate: This parameter is used only for RTP transport. It indicates the
     resolution of the timestamp field in the RTP header. If this parameter
     is not specified, the default value of 90000 (90KHz) is used.

     profile-level-id: A decimal representation of MPEG-4 Visual Profile
     Level indication value (profile_and_level_indication) defined in Table
     G-1 of ISO/IEC 14496-2 [2][4].

     mpeg4-newpred-upstream-message: A boolean number to indicate the
     receiver capability of sending the upstream message of NEWPRED in
     MPEG-4 video. The upstream messages are delivered on the particular
     RTCP packets which are described in section 5. This optional exist
     when and only when the "profile-level-id" is 145, 146, 147 or 148
     (Advance Real Time Simple Profile/Level 1, 2, 3 or 4).

     Example usages for these parameters are show bellow:
       - MPEG-4 Visual Core Profile/Level 2:
          Content-type: video/mp4v; profile-level-id=34

       - MPEG-4 Visual Advanced Real Time Simple Profile/Level 1, upstream
       message is used:
          Content-type: video/mp4v; profile-level-id=145; mpeg4-newpred-
          upstream-message=1

   Published specification:
     The specification of MPEG-4 Visual stream is presented in ISO/IEC
     14469-2[2][4][9]. The RTP payload format is described in RFCXXXX.

   Encoding considerations:
     A video bitstream must be generated according to the MPEG-4 Visual
     specification (ISO/IEC 14496-2). The video bitstream is binary data,
     and must be encoded for non-binary transport; the Base64 encoding is
     suitable for Email. This type is also defined for transfer via RTP.
     The RTP packets must be packetized according to the MPEG-4 Visual RTP
     payload format defined in RFCXXXX.

   Security considerations:
     See section 9 of RFCXXXX.

   Interoperability considerations:
     MPEG-4 Visual provides a large and rich set of tools for the coding of
     visual objects. In order to allow effective implementations of the
     standard, subsets of the MPEG-4 Visual tool sets have been identified,
     that can be used for specific applications. These subsets, called
     'Profiles', limit the tool set a decoder has to implement. For each of
     these Profiles, one or more Levels have been set, restricting the
     computational complexity. A Profile@Level combination allows:

     o a codec builder to implement only the subset of the standard he
     needs, while maintaining interworking with other MPEG-4 devices built
     to the same combination, and

     o checking whether MPEG-4 devices comply with the standard
     ('conformance testing').

     The visual stream SHALL be compliant with the MPEG-4 Visual
     Profile@Level specified by the parameter "profile-level-id". The
     interoperability between a sender and a receiver may be achieved by
     specifying the parameter "profile-level-id" in MIME content, or by
     exchanging this parameter in the capability exchange procedure.

   Applications which use this media type:
     Audio and visual streaming and conferencing tools, Internet messaging
     and e-mail applications.

   Additional information: none

   Person & email address to contact for further information:
     The authors of RFCXXXX. (See section 9)

   Intended usage: COMMON

   Author/Change controller:
     The authors of RFCXXXX. (See section 9)

6.2 SDP usage of MPEG-4 Visual
   The MIME media type video/MP4V string is mapped to fields in the Session
   Description Protocol (SDP), RFC 2327, as follows:

   o The MIME type (video) goes in SDP "m=" as the media name.

   o The MIME subtype (MP4V) goes in SDP "a=rtpmap" as the encoding name.

   o The optional parameter "rate" goes in "a=rtpmap" as clock rate.

   o The optional parameter "profile-level-id" MAY go in "a=fmtp" line. The
   optional parameter "mpeg4-newpred-upstream-message" MAY go in "a=fmtp"
   line, when and only when the "profile-level-id" is 145, 146, 147 or
   148(Advance Real Time Simple Profile/Level 1, 2, 3 or 4). The format and
   syntax of these parameters is the MIME media type string as a semicolon
   separated list of parameter=value pairs.

   The followings are some examples of the media representation in SDP:

   Simple Profile/Level 1, rate=90000(90KHz), "profile-level-id" is present
   in "a=fmtp" line:
     m=video 49170/2 RTP/AVP 98
     a=rtpmap:98 MP4V/90000
     a=fmtp:98 profile-level-id=1

   Advance Real Time Simple Profile/Level 1, rate=25(25Hz), "profile-level-
   id" and "      newpred-            mpeg4-        upstream-message" are present in "a=fmtp" line:
     m=video 49170/2 RTP/AVP 98
     a=rtpmap:98 MP4V/25
     a=fmtp:98 profile-level-id=145; mpeg4-newpred-upstream-message=1

6.3 MIME type registration of MPEG-4 Audio

   MIME media type name: audio

   MIME subtype name: MP4A

   Required parameters:
     rate: the rate parameter indicates the RTP time stamp clock rate. The
     default value is 90000. Other rates CAN be specified only if it would
     be set to the same value with the audio sampling rate (number of
     samples per second).

   Optional parameters:
     profile-level-id: a decimal representation of MPEG-4 Audio Profile
     Level indication value defined in ISO/IEC 14496-1 [11]. This parameter
     indicates the capability of subsets in MPEG-4 Audio tools.

     object: a decimal representation of MPEG-4 Audio Object Type value
     defined in ISO/IEC 14496-3 [5]. This parameter specifies the tool to
     be used by the coder. It CAN be used to limit the capability within
     the specified "profile-level-id".

     bitrate: the data rate for the audio bit stream.

     cpresent: this parameter indicates whether audio payload configuration
     data is multiplexed into the RTP payload (See section 4.1 in this
     document).

     config: a hexadecimal representation of octet string indicating the
     audio payload configuration data "StreamMuxConfig" defined in ISO/IEC
     14496-3 [5]. The configuration data is mapped into the octet string in
     an MSB-first basis. The first bit of the configuration data shall be
     located at the MSB of the first octet. In the last octet, zero-padding
     bits shall follow the configuration data, if necessary.

     ptime: RECOMMENDED duration of each packet in milliseconds.

   Published specification:
     The payload format specification is described in this document. The
     specification of encoding is provided in ISO/IEC 14496-3 [3][5].

   Encoding considerations:
     This type is only defined for transfer via RTP [RFC YYYY, draft-ietf-
     avt-rtp-new].

   Security considerations:
     See section 9 of RFCXXXX.

   Interoperability considerations:
     MPEG-4 Audio provides a large and rich set of tools for the coding of
     visual objects. In order to allow effective implementations of the
     standard, subsets of the MPEG-4 Audio tool sets have been identified
     similar to MPEG-4 Audio (See section 6.1).

     The audio stream SHALL be compliant with the MPEG-4 Audio
     Profile@Level specified by the parameter "profile-level-id". The
     interoperability between a sender and a receiver may be achieved by
     specifying the parameter "profile-level-id" in MIME content, or by
     exchanging this parameter in the capability exchange procedure.
     Furthermore, the "object" parameter can be used to limit the
     capability within the specified Profile@Level in capability exchange.

   Applications which use this media type:
     Audio and video streaming and conferencing tools.

   Additional information: none

   Personal & email address to contact for further information:
     See section 9 of RFCXXXX.

   Intended usage: COMMON

   Author/Change controller:
     See section 9 of RFCXXXX.

6.4 SDP usage of MPEG-4 Audio

   The MIME media type audio/MP4A string is assigned as mapped to fields in the candidate of Session
   Description Protocol (SDP), RFC 2327, as follows:

   o The MIME type (audio) goes in SDP "m=" as the UMT for media name.

   o The MIME subtype (MP4A) goes in SDP "a=rtpmap" as the moment.  Some other MPEG-4 Audio/Visual applications
       using encoding name.

   o The required parameter "rate" goes in "a=rtpmap" as clock rate.

   o The optional parameter "ptime" goes in SDP "a=ptime" attribute.

   o The optional parameter "profile-level-id" goes in "a=fmtp" line to
   indicate the upstream messages may be assigned coder capability. The "object" parameter goes in "a=fmtp"
   attribute. Any payload-format-specific parameters "bitrate", "cpresent"
   and "config" go in "a=fmtp" line. The format and syntax of these
   parameters is the future.

   packet MIME media type (PT): 8 bits string as a semicolon separated list of
   parameter=value pairs.

   The value followings are some examples of the packet type (PT) identifier media representation in SDP:

   For 6 kb/s CELP bitstream (the audio sampling rate of 8 kHz),
     m=audio 49230 RTP/AVP 96
     a=rtpmap:96 MP4A/8000
     a=fmtp:96 profile-level-id=9;object=8;cpresent=0;config=9128B1071070
     a=ptime:20

   For 64 kb/s AAC LC stereo bitstream (the audio sampling rate is 24 kHz),
     m=audio 49230 RTP/AVP 96
     a=rtpmap:96 MP4A/24000
     a=fmtp:96 profile-level-id=1; bitrate=64000; cpresent=0;
     config=9122620000

   In the constant
       RTCP_MP4UM (TBD).

   SSRC: 32 bits
       SSRC above two examples, the audio configuration data is not
   multiplexed into the synchronization source identifier for RTP payload and is described only in SDP.
   Furthermore, the sender of this
       packet.

   MPEG-4 Upstream Message Payload: variable "clock rate" is set to the audio sampling rate. If it is
   set to its default, the audio sampling rate can be obtained by parsing
   the "config" parameter.

   The syntax and semantics of following example shows that the MPEG-4 upstream messages are defined audio configuration data appears in
   the ISO/IEC 14496-2/3[4][5]. All messages are byte aligned.
        Normally one message RTP payload. The value specified in "config" parameter is mapped onto one RTCP packet, and several
        messages with same UMT could be continuously mapped onto one RTCP
        packet.  One message SHALL NOT be fragmented into different RTCP
        packets.

6. used as an
   initial value to setup coding parameters.

     m=audio 49230 RTP/AVP 96
     a=rtpmap:96 MP4A/90000
     a=fmtp:96 cpresent=1; config=9128B1071070

7. Security Considerations

   RTP packets using the payload format defined in this specification are
   subject to the security considerations discussed in the RTP specification
   [8]. This implies that confidentiality of the media streams is achieved
   by encryption. Because the data compression used with this payload format
   is applied end-to-end, encryption may be performed on the compressed data
   so there is no conflict between the two operations.

   This payload type does not exhibit any significant non-uniformity in the
   receiver side computational complexity for packet processing  to cause a
   potential denial-of-service threat.

7.

8. References

   1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9,
      RFC 2026, October 1996.

   2 ISO/IEC 14496-2:1999, "Information technology - Coding of audio-visual
      objects - Part2: Visual", December 1999.

   3 ISO/IEC 14496-3:1999, "Information technology - Coding of audio-visual
      objects - Part3: Audio", December 1999.

   4 ISO/IEC 14496-2:1999/FDAM1:2000, December 1999.

   5 ISO/IEC 14496-3:1999/FDAM1:2000, December 1999.

   6 ISO/IEC 14496-1:1999, "Information technology - Coding of audio-visual
      objects - Part1: Systems", December 1999.

   7  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997

   8 H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson "RTP: A Transport
      Protocol for Real Time Applications",  RFC 1889, Internet Engineering
      Task Force, January 1996.

   9  ISO/IEC 14496-2/DCOR1, October 1999.

   10 T. Turletti, C. Hitema, "RTP Payload Format for H.261 Video Streams",
      RFC 2032, Octover 1996.

8. 14496-2/COR1, "Information technology - Coding of audio-visual
      objects - Part2: Visual, Technical corrigendum 1", March 2000.

9. Author's Addresses

   Yoshihiro Kikuchi
   Toshiba corporation
   1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki, 212-8582, Japan
   Email: kiku@eel.rdc.toshiba.co.jp yoshihiro.kikuchi@toshiba.co.jp

   Yoshinori Matsui
   Matsushita Electric Industrial Co., LTD.
   1006, Kadoma, Kadoma-shi, Osaka, Japan
   Email: matsui@drl.mei.co.jp

   Toshiyuki Nomura
   NEC Corporation
   4-1-1,Miyazaki,Miyamae-ku,Kawasaki,JAPAN
   Email: t-nomura@ccm.cl.nec.co.jp

   Shigeru Fukunaga
   Oki Electric Industry Co., Ltd.
   1-2-27 Shiromi, Chuo-ku, Osaka 540-6025 Japan.
   Email: fukunaga444@oki.co.jp

   Hideaki Kimata
   Nippon Telegraph and Telephone Corporation
   1-1, Hikari-no-oka, Yokosuka-shi, Kanagawa, Japan
   Email: kimata@nttvdt.hil.ntt.co.jp

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