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. Kikuchi/Nomura/Fukunaga/Kimata/Matsui [Page 1] 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 Kikuchi/Nomura/Fukunaga/Kimata/Matsui [Page 2] 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 Kikuchi/Nomura/Fukunaga/Kimata/Matsui [Page 4] 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() Kikuchi/Nomura/Fukunaga/Kimata/Matsui [Page 5] 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. Kikuchi/Nomura/Fukunaga/Kimata/Matsui [Page 7] 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 Kikuchi/Nomura/Fukunaga/Kimata/Matsui [Page 8] 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, Kikuchi/Nomura/Fukunaga/Kimata/Matsui [Page 9] 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]. Kikuchi/Nomura/Fukunaga/Kimata/Matsui [Page 10] 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. Kikuchi/Nomura/Fukunaga/Kimata/Matsui [Page 11] 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. Kikuchi/Nomura/Fukunaga/Kimata/Matsui [Page 12] 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 Full Copyright Statement "Copyright (C) The Internet Society (date). All Rights Reserved. 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