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 RFC2119 [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 [RFC1890] 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, RFC2119, 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
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