Sustainability of Digital Formats
Planning for Library of Congress Collections
Sustainability of Digital Formats
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| Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact | |
| Full name | MP3 |
| Description | De facto file format for sound that wraps MP3_ENC bitstreams, which may be post- or prepended by the informally specified ID3 metadata blocks. |
| Production phase | Generally used for final-state, end-user delivery. |
| Relationship to other formats | |
| Contains | MP3_ENC encoded audio |
| 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. The accepted format for digital audio by the U.S. Copyright Office in the CORDS program, used until 2008 as a pilot for for electronic registration. |
| LC preference | See MP3_ENC |
| 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 patent claims | 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. The trade press, however, reported that the French company Thomson Multimedia and the German research organization Fraunhofer Institute plan to release protection elements for MP3 during 2004. (Not followed up at this Web site at this time.) |
| Normal rendering for sound | Good support. |
| Fidelity (support for high audio resolution) | See MP3_ENC |
| Support for multiple sound channels | See MP3_ENC |
| Support for downloadable or user-defined sounds, samples, and patches | None |
| Functionality beyond normal rendering for sound | None. See also ID3v2. |
| Tag type | 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 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 | First eleven bits: 11111111111 | If the encoded audio conforms to ISO/IEC specifications, the twelfth bit will also be 1. The first 12 bits are referred to as frame sync or MP3 sync word. The thirteenth bit indicates the ISO/IEC version: ISO/IES 11172-3 is 1; ISO/IEC 13818-3 is 0. The header information page for MPGEDIT software (consulted May 9, 2008) indicates that there is an unofficial encoding called "MPEG version 2.5" for which the twelfth and thirteenth bits are 01. MP3 headers are also described in File Structure section of the Wikipedia MP3 article (consulted May 9, 2008). |
| 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. |
| General | |
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