draft-ietf-avt-mpeg4-simple-06.txt

网络MPEG4IP流媒体开发源代码

Internet Engineering Task Force                         J. van der Meer
Internet Draft                                      Philips Electronics
                                                              D. Mackie
                                                         Apple Computer
                                                         V. Swaminathan
                                                  Sun Microsystems Inc.
                                                              D. Singer
                                                         Apple Computer
                                                             P. Gentric
                                                    Philips Electronics 

                                                          December 2002
                                                      Expires June 2003

   Document: draft-ietf-avt-mpeg4-simple-06.txt


   Transport of MPEG-4 Elementary Streams

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of section 10 of RFC 2026.

   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.
   
   This specification is a product of the Audio/Video Transport working
   group within the Internet Engineering Task Force. Comments are 
   solicited and should be addressed to the working group's mailing 
   list at [e-mail] and/or the authors.
   
   << Note for the RFC editor: xxxx should be replaced with the RFC 
   number that will be assigned. >> 
   
Abstract

   The MPEG Committee (ISO/IEC JTC1/SC29 WG11) is a working group in 
   ISO that produced the MPEG-4 standard. MPEG defines tools to 
   compress content such as audio-visual information into elementary 
   streams. This specification defines a simple, but generic RTP 
   payload format for transport of any non-multiplexed MPEG-4 
   elementary stream. 


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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Carriage of MPEG-4 elementary streams over RTP . . . . . . .   6
   2.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . .   6
   2.2.  MPEG Access Units  . . . . . . . . . . . . . . . . . . . .   6
   2.3.  Concatenation of Access Units  . . . . . . . . . . . . . .   6
   2.4.  Fragmentation of Access Units  . . . . . . . . . . . . . .   7
   2.5.  Interleaving . . . . . . . . . . . . . . . . . . . . . . .   7
   2.6.  Time stamp information . . . . . . . . . . . . . . . . . .   8
   2.7.  State indication of MPEG-4 system streams  . . . . . . . .   8
   2.8.  Random Access Indication . . . . . . . . . . . . . . . . .   8
   2.9.  Carriage of auxiliary information  . . . . . . . . . . . .   9
   2.10. MIME format parameters and configuring conditional field .   9
   2.11. Global structure of payload format . . . . . . . . . . . .   9
   2.12. Modes to transport MPEG-4 streams  . . . . . . . . . . . .  10
   2.13. Alignment with RFC 3016  . . . . . . . . . . . . . . . . .  10
   3.  Payload format . . . . . . . . . . . . . . . . . . . . . . .  11
   3.1.  Usage of RTP header fields and RTCP  . . . . . . . . . . .  11
   3.2.  RTP payload structure  . . . . . . . . . . . . . . . . . .  12
   3.2.1.  The AU Header Section  . . . . . . . . . . . . . . . . .  12
   3.2.1.1.  The AU-header  . . . . . . . . . . . . . . . . . . . .  12
   3.2.2.  The Auxiliary Section  . . . . . . . . . . . . . . . . .  14
   3.2.3.  The Access Unit Data Section . . . . . . . . . . . . . .  15
   3.2.3.1.  Fragmentation  . . . . . . . . . . . . . . . . . . . .  16
   3.2.3.2.  Interleaving . . . . . . . . . . . . . . . . . . . . .  16
   3.2.3.3.  Constraints for interleaving . . . . . . . . . . . . .  17
   3.2.3.4.  Crucial and non-crucial AUs with MPEG-4 System data  .  20
   3.3.  Usage of this specification  . . . . . . . . . . . . . . .  22
   3.3.1.  General  . . . . . . . . . . . . . . . . . . . . . . . .  22
   3.3.2.  The generic mode . . . . . . . . . . . . . . . . . . . .  22
   3.3.3.  Constant bit rate CELP . . . . . . . . . . . . . . . . .  23
   3.3.4.  Variable bit rate CELP . . . . . . . . . . . . . . . . .  23
   3.3.5.  Low bit rate AAC . . . . . . . . . . . . . . . . . . . .  24
   3.3.6.  High bit rate AAC  . . . . . . . . . . . . . . . . . . .  25
   3.3.7.  Additional modes . . . . . . . . . . . . . . . . . . . .  26
   4.  IANA considerations  . . . . . . . . . . . . . . . . . . . .  27
   4.1.  MIME type registration . . . . . . . . . . . . . . . . . .  27
   4.2.  Registration of mode definitions with IANA . . . . . . . .  32
   4.3.  Concatenation of parameters  . . . . . . . . . . . . . . .  32
   4.4.  Usage of SDP . . . . . . . . . . . . . . . . . . . . . . .  33
   4.4.1.  The a=fmtp keyword . . . . . . . . . . . . . . . . . . .  33
   5.  Security considerations  . . . . . . . . . . . . . . . . . .  33
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  34
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . .  34
   7.1 Normative references . . . . . . . . . . . . . . . . . . . .  34
   7.2 Informative references . . . . . . . . . . . . . . . . . . .  34
   8.  Author addresses . . . . . . . . . . . . . . . . . . . . . .  35





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       APPENDIX: Usage of this payload format . . . . . . . . . . .  37
       A. Examples of delay analysis with interleave  . . . . . . .  37
       A.1 Introduction . . . . . . . . . . . . . . . . . . . . . .  37
       A.2 De-interleaving and error concealment  . . . . . . . . .  37
       A.3 Simple Group interleave  . . . . . . . . . . . . . . . .  37
       A.3.1 Introduction . . . . . . . . . . . . . . . . . . . . .  37
       A.3.2 Determining the de-interleave buffer size  . . . . . .  38
       A.3.3 Determining the maximum displacement . . . . . . . . .  38
       A.4 More subtle group interleave . . . . . . . . . . . . . .  38
       A.4.1 Introduction . . . . . . . . . . . . . . . . . . . . .  38
       A.4.2 Determining the de-interleave buffer size  . . . . . .  39
       A.4.3 Determining the maximum displacement . . . . . . . . .  39
       A.5 Continuous interleave  . . . . . . . . . . . . . . . . .  39
       A.5.1 Introduction . . . . . . . . . . . . . . . . . . . . .  39
       A.5.2 Determining the de-interleave buffer size  . . . . . .  40
       A.5.3 Determining the maximum displacement . . . . . . . . .  41





































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1. Introduction

   The MPEG Committee is Working Group 11 (WG11) in ISO/IEC JTC1 SC29 
   that specified the MPEG-1, MPEG-2 and, more recently, the MPEG-4 
   standards [1]. The MPEG-4 standard specifies compression of 
   audio-visual data into for example an audio or video elementary 
   stream. In the MPEG-4 standard, these streams take the form of 
   audio-visual objects that may be arranged into an audio-visual scene
   by means of a scene description. Each MPEG-4 elementary stream 
   consists of a sequence of Access Units; examples of an Access Unit 
   (AU) are an audio frame and a video picture. 

   This specification defines a general and configurable payload 
   structure to transport MPEG-4 elementary streams, in particular 
   MPEG-4 audio (including speech) streams, MPEG-4 video streams and
   also MPEG-4 systems streams, such as BIFS (BInary Format for 
   Scenes), OCI (Object Content Information), OD (Object Descriptor) 
   and IPMP (Intellectual Property Management and Protection) streams.
   The RTP payload defined in this document is simple to implement and
   reasonably efficient. It allows for optional interleaving of Access
   Units (such as audio frames) to increase error resiliency in packet
   loss.

   Some types of MPEG-4 elementary streams include "crucial"
   information whose loss cannot be tolerated, but RTP does not provide
   reliable transmission so receipt of that crucial information is not
   assured.  Section 3.2.3.4 specifies how stream state is conveyed so
   that the receiver can detect the loss of crucial information and
   cease decoding until the next random access point is received.
   Applications transmitting streams that include crucial information,
   such as OD commands, BIFS commands, or programmatic content such as
   MPEG-J (Java) and ECMAScript, should include random access points
   sufficiently often, depending upon the probability of loss, to
   reduce stream corruption to an acceptable level.  An example is the
   carousel mechanism as defined by MPEG in ISO/IEC 14496-1.

   Such applications may also employ additional protocols or services
   to reduce the probability of loss.  At the RTP layer, these measures
   include payload formats and profiles for retransmission or forward
   error correction (such as in RFC 2733 [10]), which must be employed
   with due consideration to congestion control.  Another solution that
   may be appropriate for some applications is to carry RTP over TCP 
   (such as in RFC 2326 [8], section 10.12).  At the network layer, 
   resource allocation or preferential service may be available to 
   reduce the probability of loss. For a general description of methods
   to repair streaming media see RFC 2354 [9].







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   Though the RTP payload format defined in this document is capable 
   of transporting any MPEG-4 stream, other, more specific, formats 
   may exist, such as RFC 3016 [12] for transport of MPEG-4 video 
   (ISO/IEC 14496 [1] part 2).

   Configuration of the payload is provided to accommodate transport 
   of any MPEG-4 stream at any possible bit rate. However, for a 
   specific MPEG-4 elementary stream typically only very few 
   configurations are needed. So as to allow for the design of 
   simplified, but dedicated receivers, this specification requires 
   that specific modes are defined for transport of MPEG-4 streams. 
   This document defines modes for MPEG-4 CELP and AAC streams, as 
   well as a generic mode that can be used to transport any MPEG-4 
   stream. In the future new RFCs are expected to specify additional 
   modes for transport of MPEG-4 streams. 

   The RTP payload format defined in this document specifies carriage 
   of system-related information that is often equivalent to the 
   information that may be contained in the MPEG-4 Sync Layer (SL) as
   defined in MPEG-4 Systems [1]. This document does not prescribe how
   to transcode or map information from the SL to fields defined in 
   the RTP payload format. Such processing, if any, is left to the 
   discretion of the application. However, to anticipate the need for 
   transport of any additional system-related information in future, 
   an auxiliary field can be configured that may carry any such data. 
     
   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 [4].

























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2. Carriage of MPEG-4 elementary streams over RTP 

2.1 Introduction

   With this payload format a single MPEG-4 elementary stream can be 
   transported. Information on the type of MPEG-4 stream carried in 
   the payload is conveyed by MIME format parameters, for example in 
   an SDP [5] message or by other means (see section 4). These MIME 
   format parameters specify the configuration of the payload. To 
   allow for simplified and dedicated receivers, a MIME format 
   parameter is available to signal a specific mode of using this 
   payload. A mode definition MAY include the type of MPEG-4 
   elementary stream as well as the applied configuration, so as to 
   avoid the need in receivers to parse all MIME format parameters. 
   The applied mode MUST be signaled.

2.2 MPEG Access Units

   For carriage of compressed audio-visual data MPEG defines Access