RTP Payload Format for Bundled MPEG
RFC 2343
Document | Type |
RFC - Experimental
(May 1998; No errata)
Was draft-civanlar-bmpeg (avt WG)
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Authors | Reha Civanlar , Glenn Cash , Barry Haskell | ||
Last updated | 2013-03-02 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 2343 (Experimental) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
Network Working Group M. Civanlar Request for Comments: 2343 G. Cash Category: Experimental B. Haskell AT&T Labs-Research May 1998 RTP Payload Format for Bundled MPEG Status of this Memo This memo defines an Experimental Protocol for the Internet community. This memo does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (1998). All Rights Reserved. Abstract This document describes a payload type for bundled, MPEG-2 encoded video and audio data that may be used with RTP, version 2. Bundling has some advantages for this payload type particularly when it is used for video-on-demand applications. This payload type may be used when its advantages are important enough to sacrifice the modularity of having separate audio and video streams. 1. Introduction This document describes a bundled packetization scheme for MPEG-2 encoded audio and video streams using the Real-time Transport Protocol (RTP), version 2 [1]. The MPEG-2 International standard consists of three layers: audio, video and systems [2]. The audio and the video layers define the syntax and semantics of the corresponding "elementary streams." The systems layer supports synchronization and interleaving of multiple compressed streams, buffer initialization and management, and time identification. RFC 2250 [3] describes packetization techniques to transport individual audio and video elementary streams as well as the transport stream, which is defined at the system layer, using the RTP. Civanlar, et. al. Experimental [Page 1] RFC 2343 RTP Payload Format for Bundled MPEG May 1998 The bundled packetization scheme is needed because it has several advantages over other schemes for some important applications including video-on-demand (VOD) where, audio and video are always used together. Its advantages over independent packetization of audio and video are: 1. Uses a single port per "program" (i.e. bundled A/V). This may increase the number of streams that can be served e.g., from a VOD server. Also, it eliminates the performance hit when two ports are used for the separate audio and video streams on the client side. 2. Provides implicit synchronization of audio and video. This is particularly convenient when the A/V data is stored in an interleaved format at the server. 3. Reduces the header overhead. Since using large packets increases the effects of losses and delay, audio only packets need to be smaller increasing the overhead. An A/V bundled format can provide about 1% overall overhead reduction. Considering the high bitrates used for MPEG-2 encoded material, e.g. 4 Mbps, the number of bits saved, e.g. 40 Kbps, may provide noticeable audio or video quality improvement. 4. May reduce overall receiver buffer size. Audio and video streams may experience different delays when transmitted separately. The receiver buffers need to be designed for the longest of these delays. For example, let's assume that using two buffers, each with a size B, is sufficient with probability P when each stream is transmitted individually. The probability that the same buffer size will be sufficient when both streams need to be received is P times the conditional probability of B being sufficient for the second stream given that it was sufficient for the first one. This conditional probability is, generally, less than one requiring use of a larger buffer size to achieve the same probability level. 5. May help with the control of the overall bandwidth used by an A/V program. And, the advantages over packetization of the transport layer streams are: 1. Reduced overhead. It does not contain systems layer information which is redundant for the RTP (essentially they address similar issues). Civanlar, et. al. Experimental [Page 2] RFC 2343 RTP Payload Format for Bundled MPEG May 1998 2. Easier error recovery. Because of the structured packetization consistent with the application layer framing (ALF) principle, loss concealment and error recovery can be made simpler and more effective. 2. Encapsulation of Bundled MPEG Video and Audio Video encapsulation follows rules similar to the ones described in [3] for encapsulation of MPEG elementary streams. Specifically, 1. The MPEG Video_Sequence_Header, when present, will always be atShow full document text