Sustainability of Digital Formats: Planning for Library of Congress Collections
Sustainability of Digital Formats: Planning for Library of Congress Collections |
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| Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact | |
| 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 |
| 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 |
| Disclosure | Not documented |
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| 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. |
| Sound | |
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| 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. |
| Tag | Value | Note |
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| 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 audio/mp3 audio/x-mp3 audio/mpeg3 audio/x-mpeg3 audio/mpg audio/x-mpg audio/x-mpegaudio |
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 2.4.2.3, 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. |
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| History |
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