Subject: [AVT] Summary of RTP Payload format for AC-3 Streams

From: "Flaks, Jason" <[email-masked]>
Date: Tue, 4 Dec 2001 19:50:28 -0800

Hello all,

The following is a summary for my submission entitled "RTP Payload Format
for AC-3 Streams"

Draft-flaks-avt-rtp-ac3-00.txt
http://search.ietf.org/internet-drafts/draft-flaks-avt-rtp-ac3-00.txt

Summary: There exists a significant amount of AC-3 (Dolby Digital) encoded
content.  This is due in part to the mandatory requirement that audio for
DVD-video and ATSC digital television be encoded in AC-3.  As streaming of
audio and video gains in popularity it becomes increasingly important that a
method for packetizing and streaming AC-3 data is provided.

This document provides an RTP payload format for AC-3.  A general MIME type
registration for AC-3 is also presented. 

Due to the often-large ADU generated by AC-3 an intelligent method for
fragmenting is provided that makes use of 5/8ths point of an AC-3 frame. The
AC-3 specification guarantees that enough information is provided in the
first 5/8ths of the AC-3 stream so that processing can begin before
retrieval of the last 3/8ths of the frame.  A method is also provided for
interleaving low-bit rate 2-channel audio with 5.1 channel audio.  This will
allow the decoder to fall back on a 2-channel version of the audio if the
full 5.1 channel audio packet is lost or corrupted.  The use of only
2-channels allows for a lower bit-rate while maintaining a higher level of
quality.

We ask the AVT group to assist in making AC-3 an officially recognized media
type under the IETF and IANA.

Note: slides will be sent to the reflector later.

sincerly,
Jason Flaks
Dolby Laboratories

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
http://www1.ietf.org/mailman/listinfo/avt