Audio coding format: Difference between revisions

Revision as of 09:02, 27 December 2024

Revision as of 09:03, 27 December 2024

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{{short description|Digitally coded format for audio signals}}

[[File:Opus quality comparison colorblind compatible.svg|thumb|Comparison of coding efficiency between popular audio formats]]

An '''audio coding format'''<ref>The term "audio coding" can be seen in e.g. the name [[Advanced Audio Coding]], and is analogous to the term [[video coding format|video coding]]</ref> (or sometimes '''audio compression format''') is a [[Content format|content representation format]] for storage or transmission of [[digital audio]] (such as in [[digital television]], [[digital radio]] and in audio and video files). Examples of audio coding formats include [[MP3]], [[Advanced Audio Coding|AAC]], [[Vorbis]], [[FLAC]], and [[Opus (audio format)|Opus]]. A specific software or hardware implementation capable of [[Data_compression#Audio|audio compression]] and decompression to/from a specific audio coding format is called an ''[[audio codec]]''; an example of an audio codec is [[LAME]], which is one of several different codecs which implements encoding and decoding audio in the [[MP3]] audio coding format in software.

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 organizationsorganization]]s as [[technical standardsstandard]]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]]. 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 Matadata[[metadata]] such as title and other tags, and perhaps an index for fast seeking.<ref>{{Cite web | url=http://superuser.com/questions/357686/where-is-synchronization-information-stored-in-container-formats | title=Video – 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 hacks[[Hack (computer science)#In computer science|hack]]s which work by appending 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 algorithms[[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).

==Lossless, lossy, and uncompressed audio coding formats==

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===Speech===

* Linear predictive{{further|Speech coding (LPC)}}

** Adaptive predictive coding (APC)

* [[Linear predictive coding]] (LPC)

** [[Adaptive predictive coding]] (APC)

** [[Code-excited linear prediction]] (CELP)

** [[Algebraic code-excited linear prediction]] (ACELP)

** [[Relaxed code-excited linear prediction]] (RCELP)

** [[Low-delay CELP]] (LD-CELP)

** [[Adaptive Multi-Rate audio codec|Adaptive Multi-Rate]] (used in [[GSM]] and [[3GPP]])

** [[Codec 2]] (noted for its lack of patent restrictions)

** [[Speex]] (noted for its lack of patent restrictions)

* [[Modified discrete cosine transform]] (MDCT)

** [[AAC-LD]]

** [[CELT|Constrained Energy Lapped Transform]] (CELT)

** [[Opus (audio format)|Opus]] (mostly for real-time applications)

== List of lossless formats ==

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* TTA (True Audio Lossless)

* [[WavPack]] (WavPack lossless)

* [[Windows Media Audio 9 Lossless|WMA Lossless]] (Windows Media Lossless)

==See also==

* [[Comparison of audio coding formats]]

* [[Data compression#Audio]]

* [[Audio file format]]

* [[List of audio compression formats]]

== Notes ==

<references group="n" />

==References==

<references/>

{{Compression formats}}

[[Category:Audio file formats| ]]