Sustainability of Digital Formats: Planning for Library of Congress Collections

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MP3 File Format

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name MP3 File Format
Description De facto file format for sound that wraps MP3_ENC bitstreams, which may be post- or pre-pended by the informally specified ID3 metadata blocks.
Production phase Generally used for final-state, end-user delivery.
Relationship to other formats
    Contains MP3_ENC, MP3 (MPEG Layer III Audio Encoding)
    May contain ID3v1, ID3 Metadata, Version 1
    May contain ID3v2, ID3 Metadata, Version 2

Local use Explanation of format description terms

LC experience or existing holdings Used extensively as non-streaming service format for American Memory. Currently one of the accepted formats for electronic registration of audio by the U.S. Copyright Office in the eCO program.
LC preference See MP3_ENC

Sustainability factors Explanation of format description terms

Disclosure Not documented
    Documentation See MP3_ENC and its subtypes for documentation of the bitstream. See ID3 and its subtypes for documentation of the metadata blocks.
Adoption Very widely adopted for World Wide Web dissemination and playback on specialized devices.
    Licensing and patents None for the file structure; see MP3_ENC for discussion of patent claims pertaining to the bitstream.
Transparency See MP3_ENC
Self-documentation See MP3_ENC and ID3 and its subtypes.
External dependencies None
Technical protection considerations None.

Quality and functionality factors Explanation of format description terms

Normal rendering Good support.
Fidelity (high audio resolution) See MP3_ENC
Multiple channels See MP3_ENC
Support for user-defined sounds, samples, and patches None
Functionality beyond normal rendering None. See also ID3v2.

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension mp3
There is no "official" file format associated with MPEG-1 and MPEG-2 content. Many MP3 files contain both the audio bitstream and ID3 metadata.

Various auxiliary or related files exist; for example, m3u and pls files contain playlists associated with MP3; each of these formats works well with some players and not with others.
Internet Media Type audio/mpeg
From IETF (Internet Engineering Task Force) RFC 3003
Internet Media Type audio/x-mpeg
Additional examples selected from The File Extension Source.
Magic numbers Hex: FF FB 30
From The File Extension Source. The compiler of this document seeks confirmation of the accuracy of these numbers, or about their applicability to all variants of MP3. The standards document for the MP3_ENC bitstream (ISO/IEC 11172-3:1993, section, p. 20) states that MPEG-1 audio headers begins with "1111 1111 1111" (syncword) followed by "1" (for this standard), followed by "01" for layer III, followed by "1" if the stream has no redundancy, and then provides bits that indicate stream's bitrate. The bitstream "1111 1111 1111 1011" has "FFFB" as its hexadecimal equivalent.
ID3 marker ASCII: 3DI
When ID3 metadata is placed in a MP3_FF file, established conventions call for this marker. For ID3v1, the marker is positioned 10 bytes preceding the metadata. For ID3v2 data, the marker is positioned in the first 3 bytes of the file when the metadata is pre-pended and 10 bytes from the end of a file when it is post-pended.

Notes Explanation of format description terms


Format specifications Explanation of format description terms

Useful references


Last Updated: 08/10/2021