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ID3 is actually appended to MP3 files |
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Some audio coding formats are documented by a detailed [[technical specification]] document known as an '''audio coding specification'''. Some such specifications are written and approved by [[standardization organization]]s as [[technical standard]]s, and are thus known as an '''audio coding standard'''. The term 'standard' is also sometimes used for [[de facto standard|''de facto'' standards]] as well as formal standards.
Audio content encoded in a particular audio coding format is normally encapsulated within a [[container format (digital)|container format]]. As such, the user normally doesn't have a raw [[Advanced Audio Coding|AAC]] file, but instead has a .m4a [[audio file format|audio file]], which is a [[MPEG-4 Part 14]] container containing AAC-encoded audio. The container also contains [[metadata]] such as title and other tags, and perhaps an index for fast seeking.<ref>http://superuser.com/questions/357686/where-is-synchronization-information-stored-in-container-formats</ref> A notable exception is [[MP3]] files, which are raw audio coding without a container format. De facto standards for adding metadata tags such as title and artist to MP3s, such as [[ID3]], are [[Hack_(computer_science)#In_computer_science|hack]]s which work by
An audio coding format does not dictate all [[algorithm]]s used by a [[codec]] implementing the format. An important part of how lossy audio compression works is by removing data in ways humans can't hear, according to a [[psychoacoustic model]]; the implementer of an encoder has some freedom of choice in which data to remove (according to their psychoacoustic model).
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