The audio/mpeg Media Type

Network Working Group                                         M. Nilsson
Request for Comments: 3003                                 November 2000
Category: Standards Track


                       The audio/mpeg Media Type

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 (2000).  All Rights Reserved.

Abstract

   The audio layers of the MPEG-1 and MPEG-2 standards are in frequent
   use on the internet, but there is no uniform Multipurpose Internet
   Mail Extension (MIME) type for these files.  The intention of this
   document is to define the media type audio/mpeg to refer to this kind
   of contents.

   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 [RFC2119].

1.  MPEG audio

   The audio compression defined as layer I, layer II and layer III in
   the MPEG-1 [MPEG-1] and MPEG-2 [MPEG-2] standards is a popular method
   of compressing audio with a low quality loss.  The compressed audio
   is split into several small data frames, each containing a frame
   header and compressed audio data.

   The mime type audio/mpeg defines a elementary byte stream containing
   MPEG frames according to [MPEG-1] and [MPEG-2], possibly interspersed
   with non MPEG data.  Non MPEG data is data without MPEG
   synchronization or in other ways not possible to decompress without
   error.

   Typically MPEG audio meta data is concatenated with the MPEG stream,
   e.g., the meta data format ID3 puts a 128 byte data block in the end
   of the stream while ID3v2 [ID3V2] prepends a data block of variable
   size to the stream.

   NOTE: MPEG audio was not designed as a file format but as a format
   for transmitting audio streams.  As such, it does not have any well
   defined way of including meta data along with audio information.
   Some products embed meta data using zero amplitude frames or
   disguised as transmission errors.  Others embed the MPEG data in WAV
   format.

   NOTE: The audio/MPS mime type is in use in addition to the
   audio/mpeg.  The MPA [RFC 1890] sub-type refers to MPEG audio when it
   is segmented and send as a Realtime Transport Protocol (RTP) payload.

2.  Registration Information

   To: ietf-types@iana.org Subject: Registration of MIME media type
   audio/mpeg

   MIME media type name: audio

   MIME subtype name: mpeg

   Required parameters: none

   Optional parameters: none

   Encoding considerations:

       For use over internet it is assumed that lower layers take care
       of transmission errors, so audio/mpeg data MAY include MPEG
       frames generated without the optional cyclic redundancy checks
       (CRC) for improved audio quality.

       The MPEG audio data is binary data, and must be encoded for
       non-binary transport; the Base64 encoding is suitable for Email.
       Note that the MPEG audio data does not compress easily using
       lossless compression.

   Security considerations:

        MPEG is a tagged data format, and some tags are available for
        private use.  As such, arbitrary material could potentially
        be transferred in the MPEG stream, including executable content.
        Tagged data containing executable content SHOULD never be sent
        and MUST not be executed if it is received.

                                NOTE

            The requirement that such content not be executed on receipt
            is especially important since situations exist where content
            will be generated independently and therefore could contain
            executable content that the sender is unaware of.

        Audio/mpeg objects are not signed or encrypted internally.
        External security mechanisms must be employed to ensure content
        confidentiality

   Interoperability considerations:

       MPEG audio has proven to be widely interoperable across computer
       platforms.

   Published specification: see [MPEG-1] and [MPEG-2]

   Applications which use this media type:

       MPEG audio is device-, platform- and vendor-neutral and is
       supported by a wide range of encoders and decoders (players).

   Additional information:

       Magic number(s): none
       File extension(s): .mp1, .mp2, .mp3
       Macintosh File Type Code(s): MPEG
       Object Identifier(s) or OID(s): none

   Person & email address to contact for further information:

       The author of this document.

   Intended usage: COMMON

   Author/Change controller: Martin Nilsson (see section 5)

   3.  Security Considerations

   Security considerations are discussed in the security considerations
   clause of the MIME registration in section 2.

4.  References

   [ID3v2]
     Martin Nilsson, "ID3 tag version 2.3.0".
     <url:http://www.id3.org/id3v2.3.0.txt>

   [MPEG-1]
     ISO/IEC 11172-3:1993.
     Coding of moving pictures and associated audio for digital storage
     media at up to about 1,5 Mbit/s, Part 3: Audio.
     Technical committee / subcommittee: JTC 1 / SC 29

   [MPEG-2]
     ISO/IEC 13818-3:1995
     Generic coding of moving pictures and associated audio information,
     Part 3: Audio.
     Technical committee / subcommittee: JTC 1 / SC 29

     and

     ISO/IEC DIS 13818-3
     Generic coding of moving pictures and associated audio information,
     Part 3: Audio (Revision of ISO/IEC 13818-3:1995)

   [RFC2119]
     Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Levels", BCP 14, RFC 2119, March 1997.

5.  Author's Address

   Martin Nilsson
   Rydsvagen 246 C. 30
   S-584 34 Linkoping
   Sweden

   EMail: nilsson@id3.org

6.  Full Copyright Statement

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.