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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
Nilsson Standards Track [Page 1]
RFC 3003 The audio/mpeg Media Type November 2000 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. Nilsson Standards Track [Page 2]
RFC 3003 The audio/mpeg Media Type November 2000 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. Nilsson Standards Track [Page 3]
RFC 3003 The audio/mpeg Media Type November 2000 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 Nilsson Standards Track [Page 4]
RFC 3003 The audio/mpeg Media Type November 2000 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. Nilsson Standards Track [Page 5]