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Versions: 00 01 02 03 04 05 rfc3016                                     
Internet Engineering Task Force                 Yoshihiro Kikuchi - Toshiba
Internet Draft                                       Toshiyuki Nomura - NEC
Document: draft-ietf-avt-rtp-mpeg4-es-00.txt         Shigeru Fukunaga - Oki
                                              Yoshinori Matsui - Matsushita
                                                       Hideaki Kimata - NTT
                                                           February 1, 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
   may also distribute working documents as Internet-Drafts. Internet-Drafts
   are draft documents valid for a maximum of six months and may be updated,
   replaced, or obsoleted by other documents at any time. It is
   inappropriate to use Internet- Drafts as reference material or to cite
   them other than as "work in progress."
   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt
   The list of Internet-Draft Shadow Directories can be accessed at
   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]. 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.












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RTP payload format for MPEG-4 Audio/Visual streams       February 2000

1. Introduction

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

   The RTP payload formats described in this Internet-Draft specify the
   normative way on how MPEG-4 Audio/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.  MPEG-4 Audio/Visual streams are not
   managed by Object Descriptors[6] but H.245, and directly mapped into RTP
   packets without Sync Layer[6]. The semantics of RTP headers in this case
   need to be clearly 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 to
   enhance error resiliency by utilizing the error resilience tools provided
   inside the MPEG-4 Video stream.  However, they have not been studied
   until now.


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 from
   guarantied with almost error-free to mobile with high error rate by its
   error resilience functionalities.

   A normative way of fragmentation of an MPEG-4 visual bitstream into RTP
   packets is defined in this Internet draft. Since MPEG-4 Visual is used
   for a wide variety of networks, it is not desired to apply too much
   restriction on the fragmentation like a single video packet shall always
   be mapped on a single RTP packet. 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 is flexible but to define the minimum rules to prevent the
   meaningless fragmentation of e.g. splitting a header into packets.
   For video coding media such as H.261 or MPEG-1/2, the additional media
   specific RTP header works effectively for recovering e.g. a picture
   header corrupt 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

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RTP payload format for MPEG-4 Audio/Visual streams       February 2000

   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, MPEG-4 Audio/Visual has 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 these messages
   are directly mapped onto some kind of low delay RTCP packets.




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.








Kikuchi/Nomura/Fukunaga/Kimata/Matsui                        [Page 3]


RTP payload format for MPEG-4 Audio/Visual streams       February 2000

   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

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RTP payload format for MPEG-4 Audio/Visual streams       February 2000

   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, 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, header means:
   - Configuration information (Visual Object Sequence Header, Visual Object
     Header and Visual 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()


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RTP payload format for MPEG-4 Audio/Visual streams       February 2000

   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 networks with almost error-
   free to mobile networks with high error rate, it is not desired to apply
   too much restriction on the fragmentation like a single video packet
   shall always be mapped on a single RTP packet. 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.

   For video coding media such as H.261 or MPEG-1/2, the additional media
   specific RTP header works effectively for recovering e.g. a picture
   header corrupt 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 Object Layer Header(VO header, VOL
   header) follow it. Since the fragmentation rule defined in 3.2 guaranties
   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 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).


Kikuchi/Nomura/Fukunaga/Kimata/Matsui                        [Page 6]


RTP payload format for MPEG-4 Audio/Visual streams       February 2000

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

















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RTP payload format for MPEG-4 Audio/Visual streams       February 2000

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

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

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

       +------+------+------------+------+------------+------+------------+
   (d) | 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













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RTP payload format for MPEG-4 Audio/Visual streams       February 2000

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,


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RTP payload format for MPEG-4 Audio/Visual streams       February 2000

   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 in
   this section SHALL ONLY be used when it is indicated by the profile and
   level indication 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].



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RTP payload format for MPEG-4 Audio/Visual streams       February 2000

   In the case that the RTP session uses a multicast address, the MPEG-4
   upstream message packets are not transmitted to the normal RTCP
   destination transport address. Instead, these upstream message packets
   are sent directly via unicast from the decoder to the coder.  The
   destination port number of these upstream message packets is always same
   to the port number of the normal RTCP address.

   As a consequence, these upstream message packets may only be used when no
   RTP mixers or translators intervene in the path from the coder to the
   decoder.  If such intermediate systems do intervene, the address of the
   coder would no longer be present as the network-level source address in
   packets received by the decoder, and in fact, it might not be possible
   for the decoder to send packets directly to the coder.

   Some reliable multicast protocols use similar NACK control packets
   transmitted over the normal multicast distribution channel, however they
   typically use random delays to prevent a NACK implosion problem. The goal
   of such protocols is to provide reliable multicast packet delivery at the
   expense of delay, which is appropriate for applications such as a shared
   whiteboard.

   On the other hand, 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 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.

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RTP payload format for MPEG-4 Audio/Visual streams       February 2000


   upstream message type (UMT): 5 bits
       Identifies the type of the MPEG-4 upstream messages.
       0:       forbidden
       1:       MPEG-4 Visual NEWPRED
       2-63:    reserved
       In this internet-draft, only NEWPRED 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_MP4UM (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. 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. References


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




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RTP payload format for MPEG-4 Audio/Visual streams       February 2000


   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. Author's Addresses


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

Kikuchi/Nomura/Fukunaga/Kimata/Matsui                        [Page 13]

RTP payload format for MPEG-4 Audio/Visual streams       February 2000

   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
RTP payload format for MPEG-4 Audio/Visual streams       February 2000


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