Audio coding format: Difference between revisions

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Some audio coding formats are documented by a detailed [[technical specification]] document known as a '''audio coding specification'''. Some such specifications are written and approved by [[standardization organization]]s as [[technical standard]]s, and are thus known as a '''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 according using a particular audio coding format is normally used inside 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 .aacm4a [[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 tag such as title and artist to MP3s, such as [[ID3]], are [[Hack_(computer_science)#In_computer_science|hack]]s which work by prepending the tags to the MP3, and then relying on the MP3 player to recognize the chunk as malformed audio coding and therefore skip it. In video files with audio, the encoded audio content is bundled with video (in a [[video coding format]]) inside a [[multimedia container format]].

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 have some freedom of choice in which data to remove (according to their psycoaccustic model).