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



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  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: [email protected] 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.






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                               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.









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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: [email protected]















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6.  Full Copyright Statement

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

  This document and translations of it may be copied and furnished to
  others, and derivative works that comment on or otherwise explain it
  or assist in its implementation may be prepared, copied, published
  and distributed, in whole or in part, without restriction of any
  kind, provided that the above copyright notice and this paragraph are
  included on all such copies and derivative works.  However, this
  document itself may not be modified in any way, such as by removing
  the copyright notice or references to the Internet Society or other
  Internet organizations, except as needed for the purpose of
  developing Internet standards in which case the procedures for
  copyrights defined in the Internet Standards process must be
  followed, or as required to translate it into languages other than
  English.

  The limited permissions granted above are perpetual and will not be
  revoked by the Internet Society or its successors or assigns.

  This document and the information contained herein is provided on an
  "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
  TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
  BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
  HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
  MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

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



















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