Real-time Transport Protocol (RTP) Payload Format for Enhanced AC-3 (E-AC-3) Audio
RFC 4598

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Network Working Group                                            B. Link
Request for Comments: 4598                            Dolby Laboratories
Category: Standards Track                                      July 2006

                  Real-time Transport Protocol (RTP)
            Payload Format for Enhanced AC-3 (E-AC-3) Audio

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document describes a Real-time Transport Protocol (RTP) payload
   format for transporting Enhanced AC-3 (E-AC-3) encoded audio data.
   E-AC-3 is a high-quality, multichannel audio coding format and is an
   extension of the AC-3 audio coding format, which is used in US High-
   Definition Television (HDTV), DVD, cable and satellite television,
   and other media.  E-AC-3 is an optional audio format in US and world
   wide digital television and high-definition DVD formats.  The RTP
   payload format as presented in this document includes support for
   data fragmentation.

Link                        Standards Track                     [Page 1]
RFC 4598          RTP Payload Format for E-AC-3-Audio          July 2006

Table of Contents

   1. Introduction ....................................................2
   2. Overview of Enhanced-AC-3 .......................................3
      2.1. E-AC-3 Bit Stream ..........................................5
           2.1.1. Sync Frames and Audio Blocks ........................5
           2.1.2. Programs and Substreams .............................6
           2.1.3. Frame Sets ..........................................7
   3. RTP E-AC-3 Header Fields ........................................7
   4. RTP E-AC-3 Payload Format .......................................8
      4.1. Payload Specific Header ....................................8
      4.2. Fragmentation of E-AC-3 Frames .............................9
      4.3. Concatenation of E-AC-3 Frames .............................9
      4.4. Carriage of AC-3 Frames ...................................10
   5. Types and Names ................................................10
      5.1. Media Type Registration ...................................10
      5.2. SDP Usage .................................................13
   6. Security Considerations ........................................14
   7. Congestion Control .............................................15
   8. IANA Considerations ............................................15
   9. References .....................................................15
      9.1. Normative References ......................................15
      9.2. Informative References ....................................16

1.  Introduction

   The Enhanced AC-3 (E-AC-3) [ETSI] audio coding system is built on a
   foundation of AC-3.  It is an enhancement and extension to AC-3,
   which is an existing audio coding standard commonly used for DVD,
   broadcast, cable, and satellite television content.  E-AC-3 is
   designed to enable operation at both higher and lower data rates than
   AC-3, provide expanded channel configurations, and provide greater
   flexibility for carriage of multiple audio program elements.  The
   relationship between E-AC-3 and AC-3 provides for low-loss, low-cost
   conversion between the two and makes E-AC-3 especially suitable in
   applications that require compatibility with the existing broadcast-
   reception and audio/video decoding infrastructure.  Dolby Digital
   Plus is a branded version of Enhanced AC-3.

   E-AC-3 has been standardized within both the European
   Telecommunications Standards Institute (ETSI) and the Advanced
   Television Systems Committee (ATSC).  It is an optional audio format
   for use in US (ATSC) and Digital Video Broadcasting (DVB) television
   transmission.  It is also a required audio format for use in the High
   Definition (HD)-DVD optical-storage media format and included in the
   Blu-ray Disc format.

Link                        Standards Track                     [Page 2]
RFC 4598          RTP Payload Format for E-AC-3-Audio          July 2006

   There is a need to stream E-AC-3 content over IP networks.  E-AC-3 is
   primarily used in audio-for-video applications, so RTP serves well as
   a transport solution with its mechanism for synchronizing streams.
   Applications for streaming E-AC-3 include Internet Protocol
   television (IPTV), video on demand, interactive features of next
   generation DVD formats, and transfer of movies across a home network.

   Section 2 gives a brief overview of the E-AC-3 algorithm.  Section 3