MP3

MP3 is the name commonly given to the audio formats specified by MPEG-1 Layer III and MPEG-2 Layer III, standardized as ISO/IEC 11172-3:1993, with some additions in ISO/IEC 13818-3:1995. It uses lossy compressed data.

MP3 is based in part on work by the Fraunhofer Institute, which held patents in the format. Other companies may also have held patents encumbering its implementation. One of the relevant patents was U.S. Patent 5,812,672, which expired in September 2015; many other related patents in various countries expired earlier. The final expiration of all relevant patents took until 2017, however, due to some "submarine patents" which were kept in the application process for years, extending their expiration dates. A modified version of DCT compression (Discrete cosine transform) is used, a lossy compression method also used in JPEG images.

ID3 tags are often used to provide metadata in MP3 files, though they aren't part of the MP3 specification.

Specifications

 * ISO/IEC 11172-3:1993 (not free to download)
 * ISO/IEC 13818-3:1998 (not free to download)
 * RFC 3003: The audio/mpeg Media Type
 * RFC 5219: A More Loss-Tolerant RTP Payload Format for MP3 Audio
 * http://mpgedit.org/mpgedit/mpeg_format/mpeghdr.htm
 * http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html

Software

 * Konvertor
 * MP3DirectCut -- MP3 editor
 * LAME MP3 encoder: open-source
 * LAME compiled libraries - needed for various software to let it import/export/use MP3s
 * mp3stego: Hide information in MP3 files

Other links

 * MP3 (Wikipedia)
 * Now You Can 3D Print Any MP3 Into A Vinyl Record
 * Diff of 2 copies of an Amazon MP3 download showing how they have different hashes, apparently a DRM measure to uniquely identify a copy
 * The Ghost in the MP3
 * Honda MP3 player defect
 * The MP3 Is Officially Dead, According To Its Creators [Ed. note: This article title may be misleading.]