RFC 3119 (rfc3119) - Page 1 of 19

A More Loss-Tolerant RTP Payload Format for MP3 Audio

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Network Working Group                                       R. Finlayson
Request for Comments: 3119                                      LIVE.COM
Category: Standards Track                                      June 2001


         A More Loss-Tolerant RTP Payload Format for MP3 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 (2001).  All Rights Reserved.

Abstract

   This document describes a RTP (Real-Time Protocol) payload format for
   transporting MPEG (Moving Picture Experts Group) 1 or 2, layer III
   audio (commonly known as "MP3").  This format is an alternative to
   that described in RFC 2250, and performs better if there is packet
   loss.

1. Introduction

   While the RTP payload format defined in RFC 2250 [2] is generally
   applicable to all forms of MPEG audio or video, it is sub-optimal for
   MPEG 1 or 2, layer III audio (commonly known as "MP3").  The reason
   for this is that an MP3 frame is not a true "Application Data Unit" -
   it contains a back-pointer to data in earlier frames, and so cannot
   be decoded independently of these earlier frames.  Because RFC 2250
   defines that packet boundaries coincide with frame boundaries, it
   handles packet loss inefficiently when carrying MP3 data.  The loss
   of an MP3 frame will render some data in previous (or future) frames
   useless, even if they are received without loss.

   In this document we define an alternative RTP payload format for MP3
   audio.  This format uses a data-preserving rearrangement of the
   original MPEG frames, so that packet boundaries now coincide with
   true MP3 "Application Data Units", which can also (optionally) be
   rearranged in an interleaving pattern.  This new format is therefore
   more data-efficient than RFC 2250 in the face of packet loss.





Finlayson                   Standards Track
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