Audio coding format: Difference between revisions

Revision as of 20:02, 16 January 2022

Latest revision as of 08:54, 25 August 2025

(33 intermediate revisions by 14 users not shown)

Line 1:

{{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 [[Contentencoded 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 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>{{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 [[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 [[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).

Line 12:

A [[lossless compression|lossless]] audio coding format reduces the total data needed to represent a sound but can be de-coded to its original, uncompressed form. A [[lossy compression|lossy]] audio coding format additionally reduces the [[audio bit depth|bit resolution]] of the sound on top of compression, which results in far less data at the cost of irretrievably lost information.

ConsumerTransmitted (streamed) audio is most often compressed using lossy audio codecs as the smaller size is far more convenient for distribution. The most widely used audio coding formats are [[MP3]] and [[Advanced Audio Coding]] (AAC), both of which are lossy formats based on [[modified discrete cosine transform]] (MDCT) and [[perceptual coding]] algorithms.

Lossless audio coding formats such as [[FLAC]] and [[Apple Lossless]] are sometimes available, though at the cost of larger files.

[[Uncompressed audio]] formats, such as [[pulse-code modulation]] (PCM, or .wav), are also sometimes used. PCM was the standard format for [[Compact Disc Digital Audio]] (CDDA), before lossy compression eventually became the standard after the introduction of MP3.

==History==

[[File:Placa-audioPC-925.jpg|right|thumb|Solidyne 922: The world's first commercial audio bit compression [[sound card]] for PC, 1990]]

In 1950, [[Bell Labs]] filed the patent on [[differential pulse-code modulation]] (DPCM).<ref name="DPCM">{{US patent reference|inventor=C. Chapin Cutler|title=Differential Quantization of Communication Signals|number=2605361|A-Datum=1950-06-29|issue-date=1952-07-29}}</ref> [[Adaptive DPCM]] (ADPCM) was introduced by P. Cummiskey, [[Nikil Jayant|Nikil S. Jayant]] and [[James L. Flanagan]] at [[Bell Labs]] in 1973.<ref>{{cite journal|doi=10.1002/j.1538-7305.1973.tb02007.x|url=https://ieeexplore.ieee.org/document/6770730|title=Adaptive Quantization in Differential PCM Coding of Speech|year=1973|last1=Cummiskey|first1=P.|last2=Jayant|first2=N. S.|last3=Flanagan|first3=J. L.|journal=Bell System Technical Journal|volume=52|issue=7|pages=1105–1118|url-access=subscription}}</ref><ref>{{cite journal |last1=Cummiskey |first1=P. |last2=Jayant |first2=Nikil S. |last3=Flanagan |first3=J. L. |title=Adaptive quantization in differential PCM coding of speech |journal=The Bell System Technical Journal |date=1973 |volume=52 |issue=7 |pages=1105–1118 |doi=10.1002/j.1538-7305.1973.tb02007.x |issn=0005-8580}}</ref>

[[Perceptual coding]] was first used for [[speech coding]] compression, with [[linear predictive coding]] (LPC).<ref name="Schroeder2014">{{cite book |last1=Schroeder |firstfirst1=Manfred R. |title=Acoustics, Information, and Communication: Memorial Volume in Honor of Manfred R. Schroeder |date=2014 |publisher=Springer |isbn=9783319056609 |chapter=Bell Laboratories |page=388 |chapter-url=https://books.google.com/books?id=d9IkBAAAQBAJ&pg=PA388}}</ref> Initial concepts for LPC date back to the work of [[Fumitada Itakura]] ([[Nagoya University]]) and Shuzo Saito ([[Nippon Telegraph and Telephone]]) in 1966.<ref>{{cite journal |last1=Gray |first1=Robert M. |title=A History of Realtime Digital Speech on Packet Networks: Part II of Linear Predictive Coding and the Internet Protocol |journal=Found. Trends Signal Process. |date=2010 |volume=3 |issue=4 |pages=203–303 |doi=10.1561/2000000036 |url=https://ee.stanford.edu/~gray/lpcip.pdf |issn=1932-8346|doi-access=free }}</ref> During the 1970s, [[Bishnu S. Atal]] and [[Manfred R. Schroeder]] at [[Bell Labs]] developed a form of LPC called [[adaptive predictive coding]] (APC), a perceptual coding algorithm that exploited the masking properties of the human ear, followed in the early 1980s with the [[code-excited linear prediction]] (CELP) algorithm which achieved a significant compression ratio for its time.<ref name="Schroeder2014"/> Perceptual coding is used by modern audio compression formats such as [[MP3]]<ref name="Schroeder2014"/> and [[Advanced Audio Codec|AAC]].

[[Discrete cosine transform]] (DCT), developed by [[N.Nasir Ahmed (engineer)|Nasir Ahmed]], T. Natarajan and [[K. R. Rao]] in 1974,<ref name="DCT">{{cite journal |author1=Nasir Ahmed |author1-link=N. Ahmed |author2=T. Natarajan |author3=Kamisetty Ramamohan Rao |journal=IEEE Transactions on Computers |title=Discrete Cosine Transform |volume=C-23 |issue=1 |pages=90–93 |date=January 1974 |doi=10.1109/T-C.1974.223784 |s2cid=149806273 |url=https://www.ic.tu-berlin.de/fileadmin/fg121/Source-Coding_WS12/selected-readings/Ahmed_et_al.__1974.pdf |access-date=2019-10-20 |archive-date=2016-12-08 |archive-url=https://web.archive.org/web/20161208075733/https://www.ic.tu-berlin.de/fileadmin/fg121/Source-Coding_WS12/selected-readings/Ahmed_et_al.__1974.pdf |url-status=dead }}</ref> provided the basis for the [[modified discrete cosine transform]] (MDCT) used by modern audio compression formats such as MP3<ref name="Guckert">{{cite web |last1=Guckert |first1=John |title=The Use of FFT and MDCT in MP3 Audio Compression |url=http://www.math.utah.edu/~gustafso/s2012/2270/web-projects/Guckert-audio-compression-svd-mdct-MP3.pdf |website=[[University of Utah]] |date=Spring 2012 |access-date=14 July 2019}}</ref> and AAC. MDCT was proposed by J. P. Princen, A. W. Johnson and A. B. Bradley in 1987,<ref>{{cite book|doi=10.1109/ICASSP.1987.1169405|chapter-url=https://ieeexplore.ieee.org/document/1169405|chapter=Subband/Transform coding using filter bank designs based on time ___domain aliasing cancellation|title=ICASSP '87. IEEE International Conference on Acoustics, Speech, and Signal Processing|year=1987|last1=Princen|first1=J.|last2=Johnson|first2=A.|last3=Bradley|first3=A.|volume=12|pages=2161–2164|s2cid=58446992}}</ref> following earlier work by Princen and Bradley in 1986.<ref>{{cite journal|doi=10.1109/TASSP.1986.1164954|url=https://ieeexplore.ieee.org/document/1164954|title=Analysis/Synthesis filter bank design based on time ___domain aliasing cancellation|year=1986|last1=Princen|first1=J.|last2=Bradley|first2=A.|journal=IEEE Transactions on Acoustics, Speech, and Signal Processing|volume=34|issue=5|pages=1153–1161}}</ref> The MDCT is used by modern audio compression formats such as [[Dolby Digital]],<ref name="Luo">{{cite book |last1=Luo |first1=Fa-Long |title=Mobile Multimedia Broadcasting Standards: Technology and Practice |date=2008 |publisher=[[Springer Science & Business Media]] |isbn=9780387782638 |page=590 |url=https://books.google.com/books?id=l6PovWat8SMC&pg=PA590}}</ref><ref>{{cite journal |last1=Britanak |first1=V. |title=On Properties, Relations, and Simplified Implementation of Filter Banks in the Dolby Digital (Plus) AC-3 Audio Coding Standards |journal=IEEE Transactions on Audio, Speech, and Language Processing |date=2011 |volume=19 |issue=5 |pages=1231–1241 |doi=10.1109/TASL.2010.2087755|bibcode=2011ITASL..19.1231B |s2cid=897622 }}</ref> [[MP3]],<ref name="Guckert">{{cite web |last1=Guckert |first1=John |title=The Use of FFT and MDCT in MP3 Audio Compression |url=http://www.math.utah.edu/~gustafso/s2012/2270/web-projects/Guckert-audio-compression-svd-mdct-MP3.pdf |website=[[University of Utah]] |date=Spring 2012 |access-date=14 July 2019}}</ref> and [[Advanced Audio Coding]] (AAC).<ref name=brandenburg>{{cite web|url=http://graphics.ethz.ch/teaching/mmcom12/slides/mp3_and_aac_brandenburg.pdf|title=MP3 and AAC Explained|last=Brandenburg|first=Karlheinz|year=1999|url-status=live|archive-url=https://web.archive.org/web/20170213191747/https://graphics.ethz.ch/teaching/mmcom12/slides/mp3_and_aac_brandenburg.pdf|archive-date=2017-02-13}}</ref>

==List of lossy formats==

Line 31:

{| class="wikitable sortable"

|-

! rowspan="2" | Basic compression algorithm

! rowspan="2" | Audio coding standard

! rowspan="2" | Abbreviation

! rowspan="2" | Introduction

! colspan="2" | Market share {{small|(20192023)}}<ref name="Bitmovin">{{cite web |url=https://cdn2.hubspot.net/hubfs/3411032/Bitmovin%20Magazine/Video%20Developer%20Report%202019/bitmovin-video-developer-report-2019.pdf |title=Video Developer Report 2019 |website=[[Bitmovin]] |year=2019 |access-date=5 November 2019}}</ref>

! {{Abbr|Ref|Reference(s)}}

|-

!Production

| rowspan="9" | [[Modified discrete cosine transform]] (MDCT)

!Streaming

!

|-

| rowspan="911" | [[Modified discrete cosine transform]] (MDCT)

| [[Dolby Digital]] (AC-3)

| AC3

| 1991

| rowspan="2" | 36–54%{{refn|group=n|name=MarketShareNote|The report combines AC-3 & E-AC-3 and separates [[Dolby Atmos]] from its market share calculation. Dolby Atmos can be encoded either lossily with E-AC-3/[[Dolby AC-4|AC-4]]<ref>{{Cite web |date=2023-05-23 |title=Does Dolby AC-4 support Dolby Atmos? |url=https://professionalsupport.dolby.com/s/article/Does-Dolby-AC-4-support-Dolby-Atmos |access-date=2024-11-08 |website=Dolby Professional Support}}</ref> or losslessly with [[Dolby TrueHD]]. [[Music streaming service|Music]] and [[Video on demand|video streaming]] providers typically use Dolby Digital Plus augmented with Dolby Atmos, whereas [[Music download|digital downloads]] and [[Blu-ray|Blu-ray discs]] typically use Dolby TrueHD augmented with Dolby Atmos.<ref>{{Cite web |date=2023-05-03 |title=Just wait until you hear lossless Dolby Atmos Music |url=https://www.digitaltrends.com/home-theater/lossless-spatial-audio-dolby-atmos-music/ |access-date=2024-11-08 |website=Digital Trends |language=en}}</ref>}}

| 58%

| rowspan="2" |37–61%{{refn|group=n|name=MarketShareNote}}

| <ref name="Luo">{{cite book |last1=Luo |first1=Fa-Long |title=Mobile Multimedia Broadcasting Standards: Technology and Practice |date=2008 |publisher=[[Springer Science & Business Media]] |isbn=9780387782638 |page=590 |url=https://books.google.com/books?id=l6PovWat8SMC&pg=PA590}}</ref><ref name="Britanak2011">{{cite journal |last1=Britanak |first1=V. |title=On Properties, Relations, and Simplified Implementation of Filter Banks in the Dolby Digital (Plus) AC-3 Audio Coding Standards |journal=IEEE Transactions on Audio, Speech, and Language Processing |date=2011 |volume=19 |issue=5 |pages=1231–1241 |doi=10.1109/TASL.2010.2087755|bibcode=2011ITASL..19.1231B |s2cid=897622 }}</ref>

|-

|[[Dolby Digital|Dolby Digital Plus]] (E-AC-3)

| [[Adaptive Transform Acoustic Coding]]

|EAC3

|2004

|<ref>{{cite web |last1=Andersen |first1=Robert Loring |last2=Crockett |first2=B. |last3=Davidson |first3=G. |last4=Davis |first4=Mark |last5=Fielder |first5=L. |last6=Turner |first6=Stephen C. |last7=Vinton |first7=M. |last8=Williams |first8=P. |date=1 October 2004 |title=Introduction to Dolby Digital Plus, an Enhancement to the Dolby Digital Coding System |url=https://www.dolby.com/us/en/technologies/aes-convention-paper-intro-to-dolby-digital-plus.pdf |archive-url=https://web.archive.org/web/20161119192949/https://www.dolby.com/us/en/technologies/aes-convention-paper-intro-to-dolby-digital-plus.pdf |archive-date=2016-11-19 |website=Journal of The Audio Engineering Society}}</ref><ref>{{Citation |title=Digital Audio Compression (AC-3, Enhanced AC-3) Standard |date=20 September 2017 |url=https://www.etsi.org/deliver/etsi_ts/102300_102399/102366/01.04.01_60/ts_102366v010401p.pdf |access-date=21 September 2023 |publisher=European Telecommunications Standards Institute |id=ETSI TS 102 366 V1.4.1 (2017-09}}</ref>

|-

| [[ATRAC|Adaptive Transform Acoustic Coding]]

| ATRAC

| 1992

| {{unk}}

| {{unk}}
| <ref name="Luo" />

|-

| [[MPEG Layer III]]

| MP3

| 1993

| 4915%

|19%

| <ref name="Guckert">{{cite web |last1=Guckert |first1=John |title=The Use of FFT and MDCT in MP3 Audio Compression |url=http://www.math.utah.edu/~gustafso/s2012/2270/web-projects/Guckert-audio-compression-svd-mdct-MP3.pdf |website=[[University of Utah]] |date=Spring 2012 |access-date=14 July 2019}}</ref><ref name="Stankovic">{{cite journal |last1=Stanković |first1=Radomir S. |last2=Astola |first2=Jaakko T. |title=Reminiscences of the Early Work in DCT: Interview with K.R. Rao |journal=Reprints from the Early Days of Information Sciences |date=2012 |volume=60 |url=http://ticsp.cs.tut.fi/reports/ticsp-report-60-reprint-rao-corrected.pdf |access-date=13 October 2019}}</ref>

|-

| [[Advanced Audio Coding]] ([[MPEG-2]] / [[MPEG-4]])

| AAC

| 1997

| 8883%

|87%

| <ref name=brandenburg>{{cite web|url=http://graphics.ethz.ch/teaching/mmcom12/slides/mp3_and_aac_brandenburg.pdf|title=MP3 and AAC Explained|last=Brandenburg|first=Karlheinz|year=1999|url-status=live|archive-url=https://web.archive.org/web/20170213191747/https://graphics.ethz.ch/teaching/mmcom12/slides/mp3_and_aac_brandenburg.pdf|archive-date=2017-02-13}}</ref><ref name="Luo"/>

| <ref name="brandenburg" /><ref name="Luo" />

|-

| [[Windows Media Audio]]

Line 67 ⟶ 80:

| 1999

| {{unk}}

| {{unk}}
| <ref name="Luo" />

|-

| [[Ogg]] [[Vorbis]]

| Ogg

| 2000

| 76%

|4%

| <ref name="vorbis-mdct">{{cite web |author=Xiph.Org Foundation |publisher=Xiph.Org Foundation |url=http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html#x1-50001.1.2 |title=Vorbis I specification - 1.1.2 Classification |date=2009-06-02 |access-date=2009-09-22}}</ref><ref name="Luo" />

|-

| [[CELT|Constrained Energy Lapped Transform]]

| CELT

| 2011

| {{n/a}}

| {{n/a}}

| <ref name="presentation">{{cite AV media|url=http://people.xiph.org/~greg/video/linux_conf_au_CELT_2.ogv|title=Presentation of the CELT codec|first=Timothy B.|last=Terriberry|transcript-url=http://www.celt-codec.org/presentations/misc/lca-celt.pdf|transcript=Presentation}}</ref>

|-

| [[Opus (codecaudio format)|Opus]]

| Opus

| 2012

| 812%

|9%

| <ref>{{cite conference|last1=Valin|first1=Jean-Marc|last2=Maxwell|first2=Gregory|last3=Terriberry|first3=Timothy B.|last4=Vos|first4=Koen|date=October 2013|title=High-Quality, Low-Delay Music Coding in the Opus Codec|conference=135th AES Convention|publisher=[[Audio Engineering Society]]|arxiv=1602.04845}}</ref>

|-

|[[Dolby AC-4]]

|AC4

|2014

| {{unk}}

| {{unk}}

|<ref name="DolbyAC4ServicesJune2015Dolby">{{cite news |date=2015-06-01 |title=Dolby AC-4: Audio Delivery for Next-Generation Entertainment Services |url=https://www.dolby.com/in/en/technologies/ac-4/Next-Generation-Entertainment-Services.pdf |url-status=dead |archive-url=https://web.archive.org/web/20151204095813/http://www.dolby.com/in/en/technologies/ac-4/Next-Generation-Entertainment-Services.pdf |archive-date=2015-12-04 |access-date=2016-04-26 |publisher=[[Dolby Laboratories]]}}</ref>

|-

| [[LDAC (codec)|LDAC]]

| LDAC

| 2015

| {{unk}}

| {{unk}}

| <ref name="Darko 2017">{{cite web | last=Darko | first=John H. | title=The inconvenient truth about Bluetooth audio | website=DAR__KO | date=2017-03-29 | url=http://www.digitalaudioreview.net/2017/03/the-inconvenient-truth-about-bluetooth-audio/ | access-date=2018-01-13 | archive-url=https://web.archive.org/web/20180114020200/http://www.digitalaudioreview.net/2017/03/the-inconvenient-truth-about-bluetooth-audio/ | archive-date=2018-01-14 | url-status=dead }}</ref><ref name="AVHub 2015">{{cite web|url=http://www.avhub.com.au/news/sound-image/what-is-sony-ldac-and-how-does-it-do-it-408285|title=What is Sony LDAC, and how does it do it?|last=Ford|first=Jez|date=2015-08-24|website=AVHub|access-date=2018-01-13}}</ref>

Line 97 ⟶ 122:

| aptX

| 1989

| {{unk}}

| {{unk}}

| <ref name="AVHub 2016">{{cite web|url=http://www.avhub.com.au/news/sound-image/aptx-hd---lossless-or-lossy-442124|title=aptX HD - lossless or lossy?|last=Ford|first=Jez|date=2016-11-22|website=AVHub|access-date=2018-01-13}}</ref>

|-

| [[DTS (sound systemcompany)#DTS audio codecDTS_Digital_Surround|Digital Theater Systems]]

| DTS

| 1990

| 148%

|6%

| <ref>{{cite web |title=Digital Theater Systems Audio Formats |url=https://www.loc.gov/preservation/digital/formats/fdd/fdd000232.shtml |website=[[Library of Congress]] |access-date=10 November 2019 |date=27 December 2011}}</ref><ref>{{cite book |last1=Spanias |first1=Andreas |last2=Painter |first2=Ted |last3=Atti |first3=Venkatraman |title=Audio Signal Processing and Coding |date=2006 |publisher=[[John Wiley & Sons]] |isbn=9780470041963 |page=338 |url=https://books.google.com/books?id=a1RULRErhOYC&pg=PA338}}</ref>

|-

Line 110 ⟶ 137:

| 2014

| {{unk}}

| {{unk}}

|

|-

| rowspan="23" | [[Sub-band coding]] (SBC)

| [[MPEG-1 Audio Layer II]]

| MP2

| 1993

| rowspan="2" {{unk}}

| rowspan="2" | {{unk}}

|<ref name="11172-32">{{cite web |year=1993 |title=ISO/IEC 11172-3:1993 – Information technology — Coding of moving pictures and associated audio for digital storage media at up to about 1,5 Mbit/s — Part 3: Audio |url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=22412 |access-date=2010-07-14 |publisher=ISO}}</ref>

|-

| [[Musepack]]

| MPC

| 1997

|

|-

|[[SBC (codec)|SBC]]

|SBC

|2003

| {{unk}}

| {{unk}}

|<ref name="a2dp">Bluetooth SIG, Specification of the Bluetooth System, Profiles, Advanced Audio Distribution Profile version 1.3. https://www.bluetooth.org/docman/handlers/DownloadDoc.ashx?doc_id=260859&vId=290074</ref>

|}

Line 134 ⟶ 171:

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

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

** [[Codec2Codec 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 (codecaudio format)|Opus]] (mostly for real-time applications)

== List of lossless formats ==

* [[Apple Lossless Audio Codec|Apple Lossless]] (ALAC – Apple Lossless Audio Codec)

* [[ATRAC|Adaptive Transform Acoustic Coding]] (ATRAC)

* [[Audio Lossless Coding]] (also known as MPEG-4 ALS)

* [[Super Audio CD#DST|Direct Stream Transfer]] (DST)

* [[Dolby TrueHD]]

* [[DTS-HD Master Audio]]

* [[FLAC|Free Lossless Audio Codec]] (FLAC)

* [[Discrete cosine transform|Lossless discrete cosine transform]] (LDCT)

* [[Meridian Lossless Packing]] (MLP)

Line 156 ⟶ 193:

* [[Original Sound Quality]] (OSQ)

* [[RealPlayer]] (RealAudio Lossless)

* [[Shorten (file formatcodec)|Shorten]] (SHN)

* [[TTA (codec)|TTA]] (True Audio Lossless)

* [[WavPack]] (WavPack lossless)

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

Line 166 ⟶ 203:

* [[Audio file format]]

* [[List of audio compression formats]]

== Notes ==

<references group="n" />

==References==

<references/>

{{Compression formats}}

[[Category:Audio file formats| ]]