View source for Advanced Audio Coding

{{Short description|Lossy audio compression format}}
{{Prose|date=June 2024}}
{{Infobox file format
| name          = Advanced Audio Coding
| icon          = AAC original logo.svg
| icon_size     = 125
| screenshot    = 
| caption       = 
| extension     = {{code|.3gp, .aac, .adif, .adts, .m4a, .m4b, .m4p, .m4r, .mp4}}
| _noextcode    = 1
| mime          = audio/aac <br /> audio/aacp <br /> audio/3gpp <br /> audio/3gpp2 <br /> audio/mp4 <br /> audio/mp4a-latm <br /> audio/mpeg4-generic
| released      = {{start date and age|1997|12}}<ref name="iso13818-7-1997">{{cite web
 |url         = http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=25040
 |title       = ISO/IEC 13818-7:1997, Information technology — Generic coding of moving pictures and associated audio information — Part 7: Advanced Audio Coding (AAC)
 |author      = [[ISO]]
 |year        = 1997
 |access-date  = 2010-07-18
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20120925194258/http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=25040
 |archive-date = 2012-09-25
}}</ref>
| type code     = 
| uniform type  = 
| owner         = [[AT&T Labs]], [[Dolby Laboratories]], [[Fraunhofer Society]], [[Sony Corporation]]
| latest release version = ISO/IEC 14496-3:2019
| latest release date = {{Start date and age|2019|12|df=y}}
| type          = [[Lossy]] [[Audio file format|audio]]
| container for = 
| contained by  = [[MPEG-4 Part 14]], [[3GP and 3G2]], [[ISO base media file format]] and Audio Data Interchange Format (ADIF)
| extended from = 
| extended to   = 
| open          = Yes
| free          = No<ref>{{cite tech report |publisher=Library of Congress |location=Washington, D.C. |series=Sustainability of Digital Formats |type=Full draft |title=Advanced Audio Coding (MPEG-4) |date=22 June 2010 |url=https://www.loc.gov/preservation/digital/formats/fdd/fdd000114.shtml |access-date=1 December 2021}}</ref>
| standard      = [[ISO/IEC 13818-7]],<br/>[[ISO/IEC 14496-3]]
}}
'''Advanced Audio Coding''' ('''AAC''') is an [[audio coding standard]] for [[lossy]] [[digital audio]] [[Audio data compression|compression]]. It was developed by [[Dolby]], [[AT&T Labs|AT&T]], [[Fraunhofer Society|Fraunhofer]] and [[Sony]],<ref name=":3">{{Cite web |date=2002-06-09 |title=AAC in the Chips |url=https://www.stereophile.com/news/11361/index.html |access-date=2025-04-11 |website=Stereophile.com |language=en}}</ref><ref>{{Cite web |date=2000 |title=Dolby Laboratories Announces AAC Support Program |url=http://www.aac-audio.com/pdf/m.pr.0003.AACInauguration.pdf|archive-url=https://web.archive.org/web/20000823164039/http://www.aac-audio.com/pdf/m.pr.0003.AACInauguration.pdf |archive-date=23 August 2000 }}</ref><ref>{{Cite web |date=2001-04-17 |title=MP3's Competitors Line Up |url=https://www.streamingmedia.com/Articles/ReadArticle.aspx?ArticleID=63900 |access-date=2025-04-11 |website=Streaming Media Magazine |language=en-US}}</ref> originally as part of the [[MPEG-2]] specification but later improved under [[MPEG-4]].<ref name="mpeg2">ISO (2006) [http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=43345 ISO/IEC 13818-7:2006 – Information technology — Generic coding of moving pictures and associated audio information — Part 7: Advanced Audio Coding (AAC)] {{webarchive|url=https://web.archive.org/web/20160303183701/http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=43345|date=2016-03-03}}, Retrieved on 2009-08-06</ref><ref name="mpeg4">ISO (2006) [http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=42739 ISO/IEC 14496-3:2005 – Information technology — Coding of audio-visual objects — Part 3: Audio] {{webarchive|url=https://web.archive.org/web/20160413224040/http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=42739|date=2016-04-13}}, Retrieved on 2009-08-06</ref> AAC was designed to be the successor of the [[MP3]] format (MPEG-2 Audio Layer III) and generally achieves higher sound quality than MP3 at the same [[bit rate]].<ref name="brandenburg">{{cite web |last=Brandenburg |first=Karlheinz |year=1999 |title=MP3 and AAC Explained |url=http://graphics.ethz.ch/teaching/mmcom12/slides/mp3_and_aac_brandenburg.pdf |url-status=dead |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> AAC encoded audio files are typically packaged in an [[MPEG-4 Part 14|MP4]] [[Container format|container]] most commonly using the [[filename extension]] <code>.m4a</code>.<ref>{{Cite news |title=Apple seeking coder to port iTunes to Windows |url=https://www.theregister.com/2003/04/30/apple_seeking_coder_to_port/ |archive-url=http://web.archive.org/web/20240908131507/https://www.theregister.com/2003/04/30/apple_seeking_coder_to_port/ |archive-date=2024-09-08 |access-date=2025-04-11 |language=en}}</ref><ref>{{Cite web |last=says |first=James |date=2021-10-17 |title=MP3 vs. AAC (.m4a) with Allan Tépper – PES 120 – Podcast Engineering School |url=https://podcastengineeringschool.com/mp3-vs-aac-m4a-with-allan-tepper-pes-120/ |access-date=2025-04-11 |language=en-US}}</ref>

The basic profile of AAC (both MPEG-4 and MPEG-2) is called '''AAC-LC''' (''Low Complexity''). It is widely supported in the industry and has been adopted as the default or standard audio format on products including [[Apple Inc.|Apple]]'s [[iTunes Store]], [[Nintendo]]'s [[Wii]],<ref>{{Cite web |last=Caron |first=Frank |date=2007-11-14 |title=Wii Photo Channel update adds customization, removes MP3 playback |url=https://arstechnica.com/gaming/2007/11/wii-photo-channel-update-adds-customization-removes-mp3-playback/ |access-date=2025-04-11 |website=Ars Technica |language=en-US}}</ref> [[Nintendo DSi|DSi]] and [[Nintendo 3DS|3DS]] and [[Sony]]'s [[PlayStation 3]].<ref>{{Cite web |title=PS3™ {{!}} Importing audio CDs to the system storage |url=https://manuals.playstation.net/document/en/ps3/current/music/cdimport.html |access-date=2025-04-11 |website=manuals.playstation.net}}</ref> It is also further supported on various other devices and software such as [[iPhone]], [[iPod]], [[PlayStation Portable]] and [[PlayStation Vita|Vita]], [[PlayStation 5]], [[Android (operating system)|Android]] and older cell phones,<ref>{{Cite web |date=2006-05-10 |title=Sony to support AAC -- heck not to freeze over |url=https://www.engadget.com/2006-05-10-sony-to-support-aac-heck-not-to-freeze-over.html |access-date=2025-04-11 |website=Engadget |language=en-US}}</ref> digital audio players like [[Sony Walkman]] and [[SanDisk Clip]], media players such as [[VLC media player|VLC]], [[Winamp]] and [[Windows Media Player]], various in-dash [[Vehicle audio|car audio]] systems,<ref>{{Cite web |title=Pioneer Releases Car Audio Package for a Limited Time in the Overseas Markets to Commemorate the 80th Anniversary of its Foundation {{!}} News Releases {{!}} News and Events {{!}} About Us {{!}} Pioneer |url=https://global.pioneer/en/corp/news/press/index/2175/ |access-date=2025-04-11 |website=Pioneer Corporation |language=en}}</ref> and is used on [[Spotify]],<ref>{{cite web |title=Audio file formats for Spotify |url=https://artists.spotify.com/help/article/audio-file-formats |access-date=20 September 2021 |website=Spotify}}</ref> [[Apple Music]],{{efn|only used on web player, [[Google Home]], [[Amazon Alexa]], and [[Microsoft Windows]] app.}} and [[YouTube]] web streaming services.<ref>{{Cite web |last=updated |first=Joe Svetlik Contributions from Becky Scarrott last |date=2022-07-25 |title=MP3, AAC, WAV, FLAC: all the audio file formats explained |url=https://www.whathifi.com/advice/mp3-aac-wav-flac-all-the-audio-file-formats-explained |access-date=2025-04-11 |website=whathifi |language=en}}</ref> AAC has been further extended into [[HE-AAC]] (''High Efficiency'', or AAC+), which improves efficiency over AAC-LC.<ref>{{Cite web |date=2004 |title=Dolby adds High-Efficiency AAC to MPEG 4 patent pool |url=https://www.theregister.com/2004/07/20/aac_he_licensing/}}</ref> Another variant is [[AAC-LD]] (''Low Delay'').<ref>{{Cite web |last=Rose |first=Matthias |date=2012-06-28 |title=Understanding MPEG Audio Codecs From mp3 To xHE-AAC |url=https://www.electronicdesign.com/technologies/embedded/article/21796123/understanding-mpeg-audio-codecs-from-mp3-to-xhe-aac |access-date=2025-04-11 |website=Electronic Design |language=en}}</ref>

AAC supports inclusion of 48 full-[[Bandwidth (computing)|bandwidth]] (up to 96&nbsp;kHz) [[audio channel]]s in one stream plus 16 low frequency effects ([[Low-frequency effects|LFE]], limited to 120&nbsp;Hz) channels, up to 16 "coupling" or dialog channels, and up to 16 data streams. The quality for stereo is satisfactory to modest requirements at 96&nbsp;kbit/s in [[joint stereo]] mode; however, [[Transparency (data compression)|hi-fi transparency]] demands data rates of at least 128&nbsp;kbit/s ([[Variable bitrate|VBR]]). Tests{{which|date=December 2021}} of MPEG-4 audio have shown that AAC meets the requirements referred to as "transparent" for the [[ITU]] at 128&nbsp;kbit/s for stereo, and 384&nbsp;kbit/s for [[5.1]] audio.<ref>{{cite web|url=https://www.iis.fraunhofer.de/content/dam/iis/de/doc/ame/wp/FraunhoferIIS_White-Paper_AAC-Broadcast-CableTV.pdf|title=The AAC Audio Coding Family For Broadcast and Cable TV|author=<!--Not stated-->|year=2013|page=6|access-date=2024-01-29|archive-url=https://web.archive.org/web/20230928013141/https://www.iis.fraunhofer.de/content/dam/iis/de/doc/ame/wp/FraunhoferIIS_White-Paper_AAC-Broadcast-CableTV.pdf|archive-date=2023-09-28}}</ref> AAC uses only a [[modified discrete cosine transform]] (MDCT) algorithm, giving it higher compression efficiency than MP3, which uses a hybrid coding algorithm that is part MDCT and part [[FFT]].<ref name="brandenburg"/>

==History==
===Background===
The [[discrete cosine transform]] (DCT), a type of [[transform coding]] for [[lossy compression]], was proposed by [[N. Ahmed|Nasir Ahmed]] in 1972, and developed by Ahmed with T. Natarajan and [[K. R. Rao]] in 1973, publishing their results in 1974.<ref name="Ahmed">{{cite journal |last=Ahmed |first=Nasir |author-link=N. Ahmed |title=How I Came Up With the Discrete Cosine Transform |journal=[[Digital Signal Processing (journal)|Digital Signal Processing]] |date=January 1991 |volume=1 |issue=1 |pages=4–5 |doi=10.1016/1051-2004(91)90086-Z |bibcode=1991DSP.....1....4A |url=https://www.scribd.com/doc/52879771/DCT-History-How-I-Came-Up-with-the-Discrete-Cosine-Transform|url-access=subscription }}</ref><ref name="pubDCT">{{Citation |first1=Nasir |last1=Ahmed |author1-link=N. Ahmed |first2=T. |last2=Natarajan |first3=K. R. |last3=Rao |title=Discrete Cosine Transform |journal=IEEE Transactions on Computers |date=January 1974 |volume=C-23 |issue=1 |pages=90–93 |doi=10.1109/T-C.1974.223784|s2cid=149806273 }}</ref><ref name="pubRaoYip">{{Citation |last1=Rao |first1=K. R. |author-link1=K. R. Rao |last2=Yip |first2=P. |title=Discrete Cosine Transform: Algorithms, Advantages, Applications |publisher=Academic Press |location=Boston |year=1990 |isbn=978-0-12-580203-1}}</ref> This led to the development of the [[modified discrete cosine transform]] (MDCT), proposed by J. P. Princen, A. W. Johnson and A. B. Bradley in 1987,<ref>J. P. Princen, A. W. Johnson und A. B. Bradley: ''Subband/transform coding using filter bank designs based on time domain aliasing cancellation'', IEEE Proc. Intl. Conference on Acoustics, Speech, and Signal Processing (ICASSP), 2161–2164, 1987</ref> following earlier work by Princen and Bradley in 1986.<ref>John P. Princen, Alan B. Bradley: ''Analysis/synthesis filter bank design based on time domain aliasing cancellation'', IEEE Trans. Acoust. Speech Signal Processing, ''ASSP-34'' (5), 1153–1161, 1986</ref> The [[MP3]] [[audio coding standard]] introduced in 1992 used a hybrid coding algorithm that is part MDCT and part [[FFT]].<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> AAC uses a purely MDCT algorithm, giving it higher compression efficiency than MP3.<ref name="brandenburg"/> Development further advanced when [[Lars Liljeryd]] introduced a method that radically shrank the amount of information needed to store the digitized form of a song or speech.<ref>{{Cite web |last=Borland |first=John |date=March 18, 2004 |title=The sound of science |url=https://www.cnet.com/tech/services-and-software/the-sound-of-science/ |access-date=2023-04-21 |website=CNET |language=en}}</ref>

AAC was developed with the cooperation between [[AT&T Labs]], [[Dolby]], [[Fraunhofer Society|Fraunhofer IIS]] (who developed MP3) and [[Sony|Sony Corporation]].<ref name=":3" /> AAC was officially declared an international standard by the [[Moving Picture Experts Group]] in April 1997. It is specified both as ''Part 7 of the MPEG-2 standard'', and ''Subpart 4 in Part 3 of the MPEG-4 standard''.<ref name="mpeg4audio-version4-2009">{{Cite tech report |url=http://webstore.iec.ch/preview/info_isoiec14496-3%7Bed4.0%7Den.pdf |title=ISO/IEC 14496-3:2009 - Information technology -- Coding of audio-visual objects -- Part 3: Audio |date=1 September 2009 |access-date=2009-10-07 |archive-url=https://web.archive.org/web/20110614010613/http://webstore.iec.ch/preview/info_isoiec14496-3%7Bed4.0%7Den.pdf |url-status=live |archive-date=14 June 2011 |publisher=[[ISO]]/[[IEC]]}}</ref> Further companies have contributed to development in later years including [[Bell Labs]], [[LG Electronics]], [[NEC]], [[Nokia]], [[Panasonic]], [[ETRI]], [[JVC Kenwood]], [[Philips]], [[Microsoft]], and [[Nippon Telegraph and Telephone|NTT]].<ref name="aac-licensors">{{cite web |title=AAC Licensors |url=https://www.via-corp.com/licensing/aac/aac-licensors/ |access-date=15 January 2020 |website=Via Corp}}</ref><ref name="businesswire">{{cite web |date=5 January 2009 |title=Via Licensing Announces Updated AAC Joint Patent License |url=https://www.businesswire.com/news/home/20090105005026/en/Licensing-Announces-Updated-AAC-Joint-Patent-License |access-date=18 June 2019 |website=[[Business Wire]]}}</ref>

===Standardization===
{{Confusing section|date=April 2025}}
In 1997, AAC was first introduced as ''MPEG-2 Part 7'', formally known as ''[[ISO]]/[[IEC]] 13818-7:1997''. This part of MPEG-2 was a new part, since MPEG-2 already included ''MPEG-2 Part 3'', formally known as ''ISO/IEC 13818-3: MPEG-2 BC'' (Backwards Compatible).<ref name="mpeg-bc">{{cite web | url=http://www.mpeg.org/MPEG/audio/aac.html | title=AAC | website=MPEG.ORG | access-date=2009-10-28 | archive-url=https://web.archive.org/web/20091003042614/http://www.mpeg.org/MPEG/audio/aac.html | archive-date=3 October 2009 | url-status=dead }}</ref><ref name="iso13818-7-2006-pdf">{{cite web | url=http://webstore.iec.ch/preview/info_isoiec13818-7%7Bed4.0%7Den.pdf | title=ISO/IEC 13818-7, Fourth edition, Part 7 - Advanced Audio Coding (AAC) | publisher=[[ISO]] | date=15 January 2006 | access-date=2009-10-28 | url-status=live | archive-url=https://web.archive.org/web/20090306055335/http://webstore.iec.ch/preview/info_isoiec13818-7%7Bed4.0%7Den.pdf | archive-date=6 March 2009 }}</ref> Therefore, MPEG-2 Part 7 is also known as ''MPEG-2 NBC'' (Non-Backward Compatible), because it is not compatible with the [[MPEG-1]] audio formats ([[MP1]], [[MPEG-1 Audio Layer II|MP2]] and [[MP3]]).<ref name="mpeg-bc" /><ref>{{cite web | url=http://www.mp3-tech.org/aac.html | title=MPEG-2/MPEG-4 - AAC | year=2003 | first=Gabriel | last=Bouvigne | publisher=MP3'Tech | access-date=2009-10-28 | url-status=live | archive-url=https://web.archive.org/web/20100105022907/http://www.mp3-tech.org/aac.html | archive-date=2010-01-05 }}</ref><ref name="mpeg-audio-faq-bc">{{cite web | url=http://mpeg.chiariglione.org/faq/mp1-aud/mp1-aud.htm | title=MPEG Audio FAQ Version 9 - MPEG-1 and MPEG-2 BC | publisher=[[ISO]] | date=October 1998 | access-date=2009-10-28 | url-status=live | archive-url=https://web.archive.org/web/20100218081343/http://mpeg.chiariglione.org/faq/mp1-aud/mp1-aud.htm | archive-date=2010-02-18 }}</ref><ref name="mpeg-audio-florence">{{cite web|url=http://mpeg.chiariglione.org/meetings/firenze/prfloren.htm |title=Florence Press Release |publisher=[[ISO]] |date=March 1996 |access-date=2009-10-28 |url-status=dead |archive-url=https://web.archive.org/web/20100408061828/http://mpeg.chiariglione.org/meetings/firenze/prfloren.htm |archive-date=2010-04-08 }}</ref>

MPEG-2 Part 7 defined three profiles: ''Low-Complexity'' profile (AAC-LC / LC-AAC), ''Main'' profile (AAC Main) and ''Scalable Sampling Rate'' profile (AAC-SSR). AAC-LC profile consists of a base format very much like AT&T's Perceptual Audio Coding (PAC) coding format,<ref>Johnston, J. D. and Ferreira, A. J., "Sum-difference stereo transform coding", ICASSP '92, March 1992, pp. II-569-572.</ref><ref>Sinha, D. and Johnston, J. D., "Audio compression at low bit rates using a signal adaptive switched filterbank", IEEE ASSP, 1996, pp. 1053-1057.</ref><ref>Johnston, J. D., Sinha, D., Dorward, S. and Quackenbush, S., "AT&T perceptual audio coder (PAC)" in Collected Papers on Digital Audio Bit-Rate Reduction, Gilchrist, N. and Grewin, C. (Ed.), Audio Engineering Society, 1996.</ref> with the addition of [[temporal noise shaping]] (TNS),<ref>Herre, J. and Johnston, J. D., "Enhancing the performance of perceptual audio coders by using temporal noise shaping", AES 101st Convention, no. preprint 4384, 1996</ref> the [[Kaiser window]] (described below), a nonuniform [[quantizer]], and a reworking of the bitstream format to handle up to 16 stereo channels, 16 mono channels, 16 low-frequency effect (LFE) channels and 16 commentary channels in one bitstream. The Main profile adds a set of recursive predictors that are calculated on each tap of the filterbank. The [[Scalable Samping Rate Profile|SSR]] uses a 4-band [[Pseudo Quadrature Mirror Filter|PQMF]] filterbank, with four shorter filterbanks following, in order to allow for scalable sampling rates.

In 1999, MPEG-2 Part 7 was updated and included in the MPEG-4 family of standards and became known as ''[[MPEG-4 Part 3]]'', ''MPEG-4 Audio'' or ''ISO/IEC 14496-3:1999''. This update included several improvements. One of these improvements was the addition of ''[[MPEG-4 Part 3#MPEG-4 Audio Object Types|Audio Object Types]]'' which are used to allow interoperability with a diverse range of other audio formats such as [[TwinVQ]], [[CELP]], [[HVXC]], [[speech synthesis]] and [[MPEG-4 Structured Audio]]. Another notable addition in this version of the AAC standard is ''Perceptual Noise Substitution'' (PNS). In that regard, the AAC profiles (AAC-LC, AAC Main and AAC-SSR profiles) are combined with perceptual noise substitution and are defined in the MPEG-4 audio standard as Audio Object Types.<ref name="mpeg4audio-profiles">{{cite web|url=http://mpeg.chiariglione.org/tutorials/papers/icj-mpeg4-si/09-natural_audio_paper/profiles.html |title=MPEG-4 Natural Audio Coding - Audio profiles and levels |first1=Karlheinz |last1=Brandenburg |first2=Oliver |last2=Kunz |first3=Akihiko |last3=Sugiyama |website=chiariglione.org |access-date=2009-10-06 |url-status=dead |archive-url=https://web.archive.org/web/20100717130019/http://mpeg.chiariglione.org/tutorials/papers/icj-mpeg4-si/09-natural_audio_paper/profiles.html |archive-date=2010-07-17 }}</ref> MPEG-4 Audio Object Types are combined in four MPEG-4 Audio profiles: Main (which includes most of the MPEG-4 Audio Object Types), Scalable (AAC LC, AAC LTP, CELP, HVXC, TwinVQ, Wavetable Synthesis, TTSI), Speech (CELP, HVXC, TTSI) and Low Rate Synthesis (Wavetable Synthesis, TTSI).<ref name="mpeg4audio-profiles" /><ref name="mpeg4audio-version1-draft">{{cite web | url=https://www.itscj.ipsj.or.jp/sc29/open/29view/29n2603t0.pdf | title=ISO/IEC FCD 14496-3 Subpart 1 - Draft - N2203 | publisher=[[ISO]]/[[IEC]] JTC 1/SC 29/WG 11 | date=15 May 1998 | access-date=2009-10-07 }}</ref>

The reference software for MPEG-4 Part 3 is specified in MPEG-4 Part 5 and the conformance bit-streams are specified in MPEG-4 Part 4. MPEG-4 Audio remains [[backward-compatible]] with MPEG-2 Part 7.<ref name="mpeg4audio-mpeg2audio">{{cite web|url=http://mpeg.chiariglione.org/tutorials/papers/icj-mpeg4-si/09-natural_audio_paper/gacoding.html |title=MPEG-4 Natural Audio Coding - General Audio Coding (AAC based) |first1=Karlheinz |last1=Brandenburg |first2=Oliver |last2=Kunz |first3=Akihiko |last3=Sugiyama |website=chiariglione.org |year=1999 |access-date=2009-10-06 |url-status=dead |archive-url=https://web.archive.org/web/20100219233137/http://mpeg.chiariglione.org/tutorials/papers/icj-mpeg4-si/09-natural_audio_paper/gacoding.html |archive-date=2010-02-19 }}</ref>

The MPEG-4 Audio Version 2 (ISO/IEC 14496-3:1999/Amd 1:2000) defined new audio object types: the low delay AAC ([[AAC-LD]]) object type, bit-sliced arithmetic coding (BSAC) object type, parametric audio coding using [[Harmonic and Individual Lines and Noise|harmonic and individual line plus noise]] and error resilient (ER) versions of object types.<ref name="mpeg4audio-iso-2-amd">{{cite web | url=http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=31568 | title=ISO/IEC 14496-3:1999/Amd 1:2000 - Audio extensions | publisher=[[ISO]] | year=2000 | access-date=2009-10-07 | url-status=live | archive-url=https://web.archive.org/web/20110606215234/http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=31568 | archive-date=2011-06-06 }}</ref><ref name="mpeg4audio-version2">{{Cite FTP | url=ftp://ftp.tnt.uni-hannover.de/pub/MPEG/audio/mpeg4/documents/w2803/w2803_n.pdf | title=ISO/IEC 14496-3:/Amd.1 - Final Committee Draft - MPEG-4 Audio Version 2 | date=July 1999 | access-date=2009-10-07 | url-status=dead | server=[[ISO]]/[[IEC]] JTC 1/SC 29/WG 11 }}</ref><ref name="mpeg4audio2">{{cite web|url=https://sound.media.mit.edu/resources/mpeg4/audio/general/aes108_6-Parametric.pdf|title=MPEG-4 Version 2 Audio Workshop:HILN - Parametric Audio Coding|at=AES 108th Convention: MPEG-4 Version 2 Audio What is it about?|location=Paris| first1=Heiko |last1=Purnhagen | date=19 February 2000 | access-date=2009-10-07}}</ref> It also defined four new audio profiles: High Quality Audio Profile, Low Delay Audio Profile, Natural Audio Profile and Mobile Audio Internetworking Profile.<ref name="mpeg4-profiles">{{cite web|url=http://www.m4if.org/resources/profiles/audio.php |archive-url=http://webarchive.loc.gov/all/20100108152236/http://www.m4if.org/resources/profiles/audio.php |url-status=dead |archive-date=2010-01-08 |title=Levels for Audio Profiles |first1=Fernando |last1=Pereira |publisher=MPEG Industry Forum |date=October 2001 |access-date=2009-10-15 }}</ref>

The [[HE-AAC]] Profile (AAC LC with [[Spectral band replication|SBR]]) and AAC Profile (AAC LC) were first standardized in ISO/IEC 14496-3:2001/Amd 1:2003.<ref name="he-aac-amd1">{{cite web | url=http://www.iso.org/iso/catalogue_detail.htm?csnumber=38148 | title=ISO/IEC 14496-3:2001/Amd 1:2003 - Bandwidth extension | publisher=[[ISO]] | year=2003 | access-date=2009-10-07 | url-status=live | archive-url=https://web.archive.org/web/20110606054451/http://www.iso.org/iso/catalogue_detail.htm?csnumber=38148 | archive-date=2011-06-06 }}</ref> The HE-AAC v2 Profile (AAC LC with SBR and Parametric Stereo) was first specified in ISO/IEC 14496-3:2005/Amd 2:2006.<ref name="mpeg4audio-n7016">{{cite web|url=http://kikaku.itscj.ipsj.or.jp/sc29/open/29view/29n6475t.doc |title=Text of ISO/IEC 14496-3:2001/FPDAM 4, Audio Lossless Coding (ALS), new audio profiles and BSAC extensions |format=DOC |publisher=[[ISO]]/[[IEC]] JTC1/SC29/WG11/N7016 |date=11 January 2005 |access-date=2009-10-09 |url-status=dead |archive-url=https://web.archive.org/web/20140512215821/http://kikaku.itscj.ipsj.or.jp/sc29/open/29view/29n6475t.doc |archive-date=12 May 2014 }}</ref><ref name="ISO 14496-3:2005/Amd.2">{{cite web | title=Audio Lossless Coding (ALS), new audio profiles and BSAC extensions, ISO/IEC 14496-3:2005/Amd 2:2006 | url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=43026 | publisher=[[ISO]] | year=2006 | access-date=2009-10-13 | url-status=live | archive-url=https://web.archive.org/web/20120104072435/http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=43026 | archive-date=2012-01-04 }}</ref><ref name="embedded">{{cite web | title=Audio compression gets better and more complex | url=http://www.embedded.com/design/real-time-and-performance/4025543/Audio-compression-gets-better-and-more-complex | first=Mihir | last=Mody | website=Embedded.com | date=6 June 2005 | access-date=2009-10-13 | url-status=live | archive-url=https://web.archive.org/web/20160208004827/http://www.embedded.com/design/real-time-and-performance/4025543/Audio-compression-gets-better-and-more-complex | archive-date=8 February 2016 }}</ref> The Parametric Stereo audio object type used in HE-AAC v2 was first defined in ISO/IEC 14496-3:2001/Amd 2:2004.<ref name="CT-whitepaper">{{cite web|url=http://www.codingtechnologies.com/products/assets/CT_aacPlus_whitepaper.pdf |title=MPEG-4 aacPlus - Audio coding for today's digital media world|access-date=2007-01-29 |url-status=dead |archive-url=https://web.archive.org/web/20061026031407/http://www.codingtechnologies.com/products/assets/CT_aacPlus_whitepaper.pdf |archive-date=2006-10-26 }}</ref><ref name="parametric">{{cite web | title=Parametric coding for high-quality audio, ISO/IEC 14496-3:2001/Amd 2:2004 | url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=39382 | publisher=[[ISO]] | year=2004 | access-date=2009-10-13 | url-status=live | archive-url=https://web.archive.org/web/20120104071002/http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=39382 | archive-date=2012-01-04 }}</ref><ref name="3gpp26401">{{cite web | title=3GPP TS 26.401 V6.0.0 (2004-09), General Audio Codec audio processing functions; Enhanced aacPlus General Audio Codec; General Description (Release 6) | url=http://www.3gpp.org/ftp/Specs/archive/26_series/26.401/26401-600.zip | format=DOC | publisher=3GPP | date=30 September 2004 | access-date=2009-10-13 | url-status=live | archive-url=https://web.archive.org/web/20060819083421/http://www.3gpp.org/ftp/Specs/archive/26_series/26.401/26401-600.zip | archive-date=19 August 2006 }}</ref>

The current version of the AAC standard is defined in ISO/IEC 14496-3:2009.<ref name="mpeg4audio-2009">{{cite web | url=http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=53943 | title=ISO/IEC 14496-3:2009 - Information technology -- Coding of audio-visual objects -- Part 3: Audio | publisher=[[ISO]] | year=2009 | access-date=2009-10-07 | url-status=live | archive-url=https://web.archive.org/web/20110606214516/http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=53943 | archive-date=2011-06-06 }}</ref>

AAC+ v2 is also standardized by [[ETSI]] ([[European Telecommunications Standards Institute]]) as TS 102005.<ref name="CT-whitepaper" />

The [[MPEG-4 Part 3]] standard also contains other ways of compressing sound. These include lossless compression formats, synthetic audio and low bit-rate compression formats generally used for speech.

===AAC's improvements over MP3===
Advanced Audio Coding is designed to be the successor of the ''[[MPEG-1 Audio Layer 3]]'', known as MP3 format, which was specified by [[ISO]]/[[IEC]] in 11172-3 ([[MPEG-1]] Audio) and 13818-3 ([[MPEG-2]] Audio).

Improvements include:
* more [[sample rate]]s (from 8 to 96 [[kHz]]) than MP3 (16 to 48&nbsp;kHz);
* up to 48 channels (MP3 supports up to two channels in MPEG-1 mode and up to [[5.1]] channels in MPEG-2 mode);
* arbitrary [[bit rate]]s and variable frame length. Standardized constant bit rate with bit reservoir;
* higher efficiency and simpler [[filter bank]]. AAC uses a pure [[MDCT]] (modified discrete cosine transform), rather than MP3's hybrid coding (which was part MDCT and part [[FFT]]);
* higher coding efficiency for [[Stationary process|stationary signals]] (AAC uses a blocksize of 1024 or 960 samples, allowing more efficient coding than MP3's 576 sample blocks);
* higher coding accuracy for [[Transient (acoustics)|transient signals]] (AAC uses a blocksize of 128 or 120 samples, allowing more accurate coding than MP3's 192 sample blocks);
* possibility to use [[Kaiser window|Kaiser-Bessel derived]] window function to eliminate [[spectral leakage]] at the expense of widening the main lobe;
* much better handling of audio frequencies above 16&nbsp;kHz;
* more flexible [[joint stereo]] (different methods can be used in different frequency ranges);
* additional modules (tools) added to increase compression efficiency: [[Noise shaping|TNS]], backwards prediction, perceptual noise substitution (PNS), etc. These modules can be combined to constitute different encoding profiles.

Overall, the AAC format allows developers more flexibility to design codecs than MP3 does, and corrects many of the design choices made in the original MPEG-1 audio specification. This increased flexibility often leads to more concurrent encoding strategies and, as a result, to more efficient compression. This is especially true at very low bit rates where the superior stereo coding, pure MDCT, and better transform window sizes leave MP3 unable to compete.

=== Adoption ===
While the MP3 format has near-universal hardware and software support, primarily because MP3 was the format of choice during the crucial first few years of widespread music [[file-sharing]]/distribution over the internet, AAC remained a strong contender due to some unwavering industry support.<ref>{{cite web |title=AAC |url=http://wiki.hydrogenaud.io/index.php?title=AAC |url-status=live |archive-url=https://web.archive.org/web/20140706172307/http://wiki.hydrogenaud.io/index.php?title=AAC |archive-date=2014-07-06 |access-date=2011-01-24 |publisher=Hydrogenaudio}}</ref> Due to MP3's dominance, adoption of AAC was initially slow. The first commercialization was in 1997 when [[AT&T Labs]] (a co-owner of AAC patents) launched a digital music store with songs encoded in MPEG-2 AAC.<ref name=":2">{{Cite web |date=2001-08-08 |title=News: A higher standard for digital music |website=[[ZDNet]] |url=https://www.zdnet.com/zdnn/stories/comment/0,5859,2699666,00.html |access-date=2025-04-11 |archive-url=https://web.archive.org/web/20010808234826/https://www.zdnet.com/zdnn/stories/comment/0,5859,2699666,00.html |archive-date=8 August 2001 }}</ref> HomeBoy for Windows was one of the earliest available AAC encoders and decoders.<ref>{{Cite web |title=ReallyRareWares - HomeBoy AAC encoder |url=https://www.rarewares.org/rrw/homeboy.php |access-date=2025-04-11 |website=www.rarewares.org}}</ref>

[[Dolby Laboratories]] came in charge of AAC licensing in 2000.<ref name=":2" /> A new licensing model was launched by Dolby in 2002, while [[Nokia]] became a fifth co-licenser of the format.<ref>{{Cite web |last=RadioWorld |date=2002-03-26 |title=Dolby Laboratories Reveals MPEG-4 AAC Licensing Program |url=https://www.radioworld.com/news-and-business/dolby-laboratories-reveals-mpeg4-aac-licensing-program |access-date=2025-04-11 |website=Radio World |language=en-US}}</ref> Dolby itself also marketed its own coding format, [[Dolby AC-3]].

Nokia started supporting AAC playback on devices as early as 2001,<ref>{{Cite web |title=Carrying A Tune With Nokia Phones |url=https://www.forbes.com/2001/08/30/0830tentech.html |access-date=2025-04-11 |website=Forbes |language=en}}</ref> but it was the exclusive use of AAC by Apple Computer for their [[iTunes Store]] which accelerated attention to AAC. Soon the format was also supported by Sony for their [[PlayStation Portable]] (albeit Sony continued promoting its proprietary [[ATRAC]]), and music-oriented cell phones from [[Sony Ericsson]] beginning with the [[Sony Ericsson W800]].<ref>{{Cite magazine |author=WIRED Staff |title=A Music File by Any Other Name |url=https://www.wired.com/2005/12/a-music-file-by-any-other-name/ |access-date=2025-04-11 |magazine=Wired |language=en-US |issn=1059-1028}}</ref> The [[Windows Media Audio]] (WMA) format, from Microsoft, was considered to be AAC's main competitor.<ref>{{Cite magazine |last=Buskirk |first=Eliot Van |title=In EMI-ITunes Deal, the Big Loser May Be Microsoft |url=https://www.wired.com/2007/04/in-emi-itunes-deal-the-big-loser-may-be-microsoft/ |access-date=2025-04-11 |magazine=Wired |language=en-US |issn=1059-1028}}</ref>

By 2017, AAC was considered to have become a ''de facto'' industry standard for lossy audio.<ref>{{Cite web |author1=What Hi-Fi Admin |date=2017-05-15 |title=Home |url=https://www.whathifi.com/news/mp3-dead-creators-end-licensing-programme |access-date=2025-04-11 |website=whathifi |language=en}}</ref>

==Functionality==
AAC is a [[wideband audio]] coding algorithm that exploits two primary coding strategies to dramatically reduce the amount of data needed to represent high-quality digital audio:
* Signal components that are perceptually irrelevant are discarded.
* Redundancies in the coded audio signal are eliminated.

The actual encoding process consists of the following steps:
* The signal is converted from time-domain to frequency-domain using forward [[modified discrete cosine transform|modified discrete cosine transform (MDCT)]]. This is done by using filter banks that take an appropriate number of time samples and convert them to frequency samples.
* The frequency domain signal is quantized based on a [[psychoacoustic]] model and encoded.
* Internal error correction codes are added.
* The signal is stored or transmitted.
* In order to prevent corrupt samples, a modern implementation of the [[Luhn mod N algorithm]] is applied to each frame.<ref>US patent application [http://www.freepatentsonline.com/y2007/0297624.html 20070297624] ''Digital audio encoding''</ref>

The [[MPEG-4]] audio standard does not define a single or small set of highly efficient compression schemes but rather a complex toolbox to perform a wide range of operations from low bit rate speech coding to high-quality audio coding and music synthesis.

* The [[MPEG-4]] audio coding algorithm family spans the range from low bit rate speech encoding (down to 2&nbsp;kbit/s) to high-quality audio coding (at 64&nbsp;kbit/s per channel and higher).
* AAC offers sampling frequencies between 8&nbsp;kHz and 96&nbsp;kHz and any number of channels between 1 and 48.
* In contrast to MP3's hybrid filter bank, AAC uses the modified discrete cosine transform ([[MDCT]]) together with the increased window lengths of 1024 or 960 points.

AAC encoders can switch dynamically between a single MDCT block of length 1024 points or 8 blocks of 128 points (or between 960 points and 120 points, respectively).
* If a signal change or a transient occurs, 8 shorter windows of 128/120 points each are chosen for their better temporal resolution.
* By default, the longer 1024-point/960-point window is otherwise used because the increased frequency resolution allows for a more sophisticated psychoacoustic model, resulting in improved coding efficiency.

===Modular encoding===
AAC takes a modular approach to encoding. Depending on the complexity of the bitstream to be encoded, the desired performance and the acceptable output, implementers may create profiles to define which of a specific set of tools they want to use for a particular application.

The MPEG-2 Part 7 standard (Advanced Audio Coding) was first published in 1997 and offers three default profiles:<ref name="iso13818-7-1997" /><ref name="iso13818-7-2004-pdf">{{cite web|url=http://jongyeob.com/moniwiki/pds/upload/13818-7.pdf |archive-url=https://web.archive.org/web/20110713115817/http://jongyeob.com/moniwiki/pds/upload/13818-7.pdf |url-status=dead |archive-date=13 July 2011 |title=ISO/IEC 13818-7, Third edition, Part 7 - Advanced Audio Coding (AAC) |publisher=[[ISO]] |page=32 |date=15 October 2004 |access-date=2009-10-19 }}</ref>

* '''Low Complexity (LC)''' – the simplest and most widely used and supported
* '''Main Profile (Main)''' – like the LC profile, with the addition of backwards prediction
* '''[[MPEG-4 AAC-SSR|Scalable Sample Rate (SSR)]]''' a.k.a. Sample-Rate Scalable (SRS)

The MPEG-4 Part 3 standard (MPEG-4 Audio) defined various new compression tools (a.k.a. [[MPEG-4 Part 3#MPEG-4 Audio Object Types|Audio Object Types]]) and their usage in brand new profiles. AAC is not used in some of the MPEG-4 Audio profiles. The MPEG-2 Part 7 AAC LC profile, AAC Main profile and AAC SSR profile are combined with Perceptual Noise Substitution and defined in the MPEG-4 Audio standard as Audio Object Types (under the name AAC LC, AAC Main and AAC SSR). These are combined with other Object Types in MPEG-4 Audio profiles.<ref name="mpeg4audio-profiles"/> Here is a list of some audio profiles defined in the MPEG-4 standard:<ref name="mpeg4audio-n7016"/><ref name="fhg-mpeg4audio">{{Cite conference|conference=109th AES Convention 2000 September 22–25 Los Angeles |url=http://www.iis.fraunhofer.de/fhg/Images/AES5270_MPEG-4_Audio_Components_on_various_Platforms_tcm278-67534.PDF |title=Implementation of MPEG-4 Audio Components on various Platforms |first1=Bernhard |last1=Grill |first2=Stefan |last2=Geyersberger |first3=Johannes |last3=Hilpert |first4=Bodo |last4=Teichmann |publisher=Fraunhofer Gesellschaft |date=July 2004 |access-date=2009-10-09 |url-status=dead |archive-url=https://web.archive.org/web/20070610222853/http://www.iis.fraunhofer.de/fhg/Images/AES5270_MPEG-4_Audio_Components_on_various_Platforms_tcm278-67534.PDF |archive-date=2007-06-10 }}</ref>
{{Main|MPEG-4 Part 3#Audio Profiles|l1=MPEG-4 Part 3: Audio Profiles}}

* '''Main Audio Profile''' – defined in 1999, uses most of the MPEG-4 Audio Object Types (AAC Main, AAC-LC, AAC-SSR, AAC-LTP, AAC Scalable, TwinVQ, CELP, HVXC, TTSI, Main synthesis)
* '''Scalable Audio Profile''' – defined in 1999, uses AAC-LC, AAC-LTP, AAC Scalable, TwinVQ, CELP, HVXC, TTSI
* '''Speech Audio Profile''' – defined in 1999, uses CELP, HVXC, TTSI
* '''Synthetic Audio Profile''' – defined in 1999, TTSI, Main synthesis
* '''High Quality Audio Profile''' – defined in 2000, uses AAC-LC, AAC-LTP, AAC Scalable, CELP, ER-AAC-LC, ER-AAC-LTP, ER-AAC Scalable, ER-CELP
* '''Low Delay Audio Profile''' – defined in 2000, uses CELP, HVXC, TTSI, ER-AAC-LD, ER-CELP, ER-HVXC
* '''Low Delay AAC v2''' - defined in 2012, uses AAC-LD, AAC-ELD and AAC-ELDv2<ref>{{Cite web|url=http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=59635|title=ISO/IEC 14496-3:2009/Amd 3:2012 - Transport of unified speech and audio coding (USAC)|website=ISO|access-date=2016-08-03|url-status=live|archive-url=https://web.archive.org/web/20160308175637/http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=59635|archive-date=2016-03-08}}</ref>
* '''Mobile Audio Internetworking Profile''' – defined in 2000, uses ER-AAC-LC, ER-AAC-Scalable, ER-TwinVQ, ER-BSAC, ER-AAC-LD
* '''AAC Profile''' – defined in 2003, uses AAC-LC
* '''High Efficiency AAC Profile''' – defined in 2003, uses AAC-LC, SBR
* '''High Efficiency AAC v2 Profile''' – defined in 2006, uses AAC-LC, SBR, PS
* '''Extended High Efficiency AAC xHE-AAC''' – defined in 2012, uses [[Unified Speech and Audio Coding|USAC]]
One of many improvements in MPEG-4 Audio is an Object Type called Long Term Prediction (LTP), which is an improvement of the Main profile using a forward predictor with lower computational complexity.<ref name="mpeg4audio-mpeg2audio" />

===AAC error protection toolkit===
Applying error protection enables error correction up to a certain extent. Error correcting codes are usually applied equally to the whole payload. However, since different parts of an AAC payload show different sensitivity to transmission errors, this would not be a very efficient approach.

The AAC payload can be subdivided into parts with different error sensitivities.
* Independent error correcting codes can be applied to any of these parts using the Error Protection (EP) tool defined in MPEG-4 Audio standard.
* This toolkit provides the error correcting capability to the most sensitive parts of the payload in order to keep the additional overhead low.
* The toolkit is backwardly compatible with simpler and pre-existing AAC decoders. A great deal of the toolkit's error correction functions are based around spreading information about the audio signal more evenly in the datastream.

===Error Resilient (ER) AAC===
Error Resilience (ER) techniques can be used to make the coding scheme itself more robust against errors.

For AAC, three custom-tailored methods were developed and defined in MPEG-4 Audio
* '''Huffman Codeword Reordering (HCR)''' to avoid error propagation within spectral data
* '''Virtual Codebooks (VCB11)''' to detect serious errors within spectral data
* '''Reversible Variable Length Code (RVLC)''' to reduce error propagation within scale factor data

===AAC Low Delay===
{{Main|AAC-LD|}}

The audio coding standards '''MPEG-4 Low Delay''' ([[AAC-LD]]), '''Enhanced Low Delay''' (AAC-ELD), and '''Enhanced Low Delay v2''' (AAC-ELDv2) as defined in ISO/IEC 14496-3:2009 and ISO/IEC 14496-3:2009/Amd 3 are designed to combine the advantages of perceptual audio coding with the low delay necessary for two-way communication. They are closely derived from the MPEG-2 Advanced Audio Coding (AAC) format.<ref>{{Cite web|url=http://www.iso.org/iso/catalogue_detail?csnumber=53943|title=ISO/IEC 14496-3:2009 - Information technology -- Coding of audio-visual objects -- Part 3: Audio|website=ISO|access-date=2016-08-02|url-status=live|archive-url=https://web.archive.org/web/20160520232358/http://www.iso.org/iso/catalogue_detail?csnumber=53943|archive-date=2016-05-20}}</ref><ref>{{Cite web|url=http://www.iso.org/iso/catalogue_detail.htm?csnumber=59635|title=ISO/IEC 14496-3:2009/Amd 3:2012 - Transport of unified speech and audio coding (USAC)|website=ISO|access-date=2016-08-02|url-status=live|archive-url=https://web.archive.org/web/20160819222620/http://www.iso.org/iso/catalogue_detail.htm?csnumber=59635|archive-date=2016-08-19}}</ref><ref>{{Cite web|url=http://mpeg.chiariglione.org/standards/mpeg-4/audio/aac-eld-family-high-quality-communication-services|title=The AAC-ELD Family for High Quality Communication Services {{!}} MPEG|website=mpeg.chiariglione.org|access-date=2016-08-02|url-status=live|archive-url=https://web.archive.org/web/20160820105628/http://mpeg.chiariglione.org/standards/mpeg-4/audio/aac-eld-family-high-quality-communication-services|archive-date=2016-08-20}}</ref> AAC-ELD is recommended by [[GSMA]] as super-wideband voice codec in the IMS Profile for High Definition Video Conference (HDVC) Service.<ref>{{Cite book|url=http://www.gsma.com/newsroom/wp-content/uploads//IR.39-v7.0.pdf|title=IMS Profile for High Definition Video Conference (HDVC) Service|publisher=GSMA|date=24 May 2016|pages=10|url-status=live|archive-url=https://web.archive.org/web/20160818201412/http://www.gsma.com/newsroom/wp-content/uploads//IR.39-v7.0.pdf|archive-date=18 August 2016}}</ref>

==Licensing and patents==
No licenses or payments are required for a user to stream or distribute audio in AAC format.<ref>{{cite web | url = https://www.via-corp.com/licensing/aac/aac-faqs/ | title = AAC Licensing FAQ Q5 | publisher = Via Licensing | access-date=2020-01-15 }}</ref> This reason alone might have made AAC a more attractive format to distribute audio than its predecessor MP3, particularly for streaming audio (such as Internet radio) depending on the use case.

However, a patent license is required for all manufacturers or developers of AAC "end-user" [[codecs]].<ref>{{cite web| url = https://www.via-corp.com/licensing/aac/license-fees/ | title = AAC License Fees | publisher = Via Licensing |access-date=2020-01-15 }}</ref> The terms (as disclosed to SEC) uses per-unit pricing. In the case of software, each computer running the software is to be considered a separate "unit".<ref name="license-ag">{{cite web |author1=Via Licensing Corporation |title=AAC PATENT LICENSE AGREEMENT |url=https://www.sec.gov/Archives/edgar/data/1649009/000121390020023370/ea125930ex10-9_siyatamobile.htm |website=www.sec.gov |access-date=21 April 2023 |date=June 5, 2018}}</ref>

It used to be common for [[free and open source software]] implementations such as [[FFmpeg]] and [[FAAC]] to only distribute in [[source code]] form so as to not "otherwise supply" an AAC codec. However, FFmpeg has since become more lenient on patent matters: the "gyan.dev" builds recommended by the official site now contain its AAC codec, with the FFmpeg legal page stating that patent law conformance is the user's responsibility.<ref>{{cite web |title=FFmpeg License and Legal Considerations |url=https://ffmpeg.org/legal.html |website=ffmpeg.org}}</ref> (See below under Products that support AAC, Software.) The [[Fedora Project]], a community backed by [[Red Hat]], has imported the "Third-Party Modified Version of the Fraunhofer FDK AAC Codec Library for Android" to its repositories on September 25, 2018,<ref>{{cite web |title=Commit - rpms/fdk-aac-free - b27d53fbad872ea0ec103653fddaec83238132d9 - src.fedoraproject.org |url=https://src.fedoraproject.org/rpms/fdk-aac-free/c/b27d53fbad872ea0ec103653fddaec83238132d9?branch=rawhide |website=src.fedoraproject.org}}</ref> and has enabled FFmpeg's native AAC encoder and decoder for its ffmpeg-free package on January 31, 2023.<ref>{{cite web |title=Commit - rpms/ffmpeg - 45f894ec0e43a37775393c159021a4ac60170a55 - src.fedoraproject.org |url=https://src.fedoraproject.org/rpms/ffmpeg/c/45f894ec0e43a37775393c159021a4ac60170a55?branch=rawhide |website=src.fedoraproject.org}}</ref>

The AAC patent holders include [[Bell Labs]], [[Dolby]], [[ETRI]], [[Fraunhofer Society|Fraunhofer]], [[JVC Kenwood]], [[LG Electronics]], [[Microsoft]], [[NEC]], [[Nippon Telegraph and Telephone|NTT]] (and its subsidiary [[NTT Docomo]]), [[Panasonic]], [[Philips]], and [[Sony Corporation]].<ref name="aac-licensors"/><ref name="businesswire"/> Based on the list of patents from the SEC terms, the last baseline AAC patent expires in 2028, and the last patent for all AAC extensions mentioned expires in 2031.<ref>{{cite web |title=List of AAC related patents |url=https://hydrogenaud.io/index.php/topic,121109.0.html |website=hydrogenaud.io}}</ref>

==Extensions and improvements==
Some extensions have been added to the first AAC standard (defined in MPEG-2 Part 7 in 1997):
* '''Perceptual Noise Substitution (PNS)''', added in [[MPEG-4 Part 3|MPEG-4]] in 1999. It allows the coding of noise as [[pseudorandom]] data.
* '''Long Term Predictor (LTP)''', added in MPEG-4 in 1999. It is a forward predictor with lower computational complexity.<ref name="mpeg4audio-mpeg2audio" />
* '''Error Resilience (ER)''', added in MPEG-4 Audio version 2 in 2000, used for transport over error prone channels<ref name="mpeg-audio-faq">{{cite web | url=http://mpeg.chiariglione.org/faq/mp4-aud/mp4-aud.htm | title=MPEG Audio FAQ Version 9 - MPEG-4 | first1=D. | last1=Thom | first2=H. | last2=Purnhagen | publisher=MPEG Audio Subgroup | website=chiariglione.org | date=October 1998 | access-date=2009-10-06 | url-status=live | archive-url=https://web.archive.org/web/20100214205916/http://mpeg.chiariglione.org/faq/mp4-aud/mp4-aud.htm | archive-date=2010-02-14 }}</ref>
*'''[[AAC-LD]]''' (Low Delay), defined in 2000, used for real-time conversation applications
*'''[[High-Efficiency Advanced Audio Coding|High Efficiency AAC]] (HE-AAC)''', a.k.a. aacPlus v1 or AAC+, the combination of [[Spectral band replication|SBR (Spectral Band Replication)]] and AAC LC. Used for low bitrates. Defined in 2003.
*'''[[HE-AAC v2]]''', a.k.a. aacPlus v2, eAAC+ or Enhanced aacPlus, the combination of [[Parametric Stereo|Parametric Stereo (PS)]] and HE-AAC; used for even lower bitrates. Defined in 2004 and 2006.
*'''[[xHE-AAC#xHE-AAC|xHE-AAC]]''', extends the operating range of the codec from 12 to 300 kbit/s.<ref name=":1">{{Cite web|title=The xHE-AAC Trademark Program|url=https://www.iis.fraunhofer.de/en/ff/amm/broadcast-streaming/xheaac/trademark-program.html|access-date=2021-02-11|website=Fraunhofer Institute for Integrated Circuits IIS|language=en}}</ref><ref name=":0">{{Cite web|title=Fraunhofer's xHE-AAC Audio Codec Software Extends Native AAC Support In Android P For Better Quality At Low Bitrates|url=https://www.iis.fraunhofer.de/en/pr/2018/20180608_AME_Android.html|access-date=2020-07-11|website=Fraunhofer Institute for Integrated Circuits IIS|language=en}}</ref>
*'''[[MPEG-4 SLS|MPEG-4 Scalable To Lossless (SLS)]]''', Not yet published,<ref>{{Cite web|title=ISO/IEC 14496-3:2019|url=https://www.iso.org/cms/render/live/en/sites/isoorg/contents/data/standard/07/63/76383.html|access-date=2022-02-19|website=ISO|language=en}}</ref> can supplement an AAC stream to provide a lossless decoding option, such as in Fraunhofer IIS's "HD-AAC" product

==Container formats{{Anchor|LATM|LOAS}}==
{{Main|MPEG-4 Part 3#Audio storage and transport|l1=MPEG-4 Part 3: Audio storage and transport}}
{{See also|Comparison of video container formats#Audio coding formats support}}
In addition to the [[MP4]], [[3GP]] and other container formats based on [[ISO base media file format]] for file storage, AAC audio data was first packaged in a file for the MPEG-2 standard using Audio Data Interchange Format (ADIF),<ref name="aes2003">{{Cite conference|last1=Wolters |first1=Martin |first2=Kristofer |last2=Kjorling |first3=Daniel |last3=Homm |first4=Heiko |last4=Purnhagen |title=A closer look into MPEG-4 High Efficiency AAC |page=3 |url=http://www.telos-systems.com/techtalk/hosted/HE-AAC.pdf |access-date=2008-07-31 |url-status=dead |archive-url=https://web.archive.org/web/20031219000444/http://telos-systems.com/techtalk/hosted/HE-AAC.pdf |archive-date=2003-12-19 }} Presented at the 115th Convention of the Audio Engineering Society, 10–13 October 2003.</ref> consisting of a single header followed by the raw AAC audio data blocks.<ref name="diipp">{{cite web|url=http://www.digitalpreservation.gov/formats/fdd/fdd000112.shtml|title=Advanced Audio Coding (MPEG-2), Audio Data Interchange Format |publisher=Library of Congress / National Digital Information Infrastructure and Preservation Program |date=7 March 2007 |access-date=2008-07-31 | archive-url= https://web.archive.org/web/20080730205354/http://www.digitalpreservation.gov/formats/fdd/fdd000112.shtml | archive-date= 30 July 2008  | url-status= live}}</ref> However, if the data is to be streamed within an MPEG-2 transport stream, a self-synchronizing format called an '''Audio Data Transport Stream''' ('''ADTS''') is used, consisting of a series of frames, each frame having a header followed by the AAC audio data.<ref name="aes2003"/> This file and streaming-based format are defined in [[MPEG-2 Part 7]], but are only considered informative by MPEG-4, so an MPEG-4 decoder does not need to support either format.<ref name="aes2003"/> These containers, as well as a raw AAC stream, may bear the .aac file extension. [[MPEG-4 Part 3]] also defines its own self-synchronizing format called a Low Overhead Audio Stream (LOAS) that encapsulates not only AAC, but any MPEG-4 audio compression scheme such as [[TwinVQ]] and [[Audio Lossless Coding|ALS]]. This format is what was defined for use in DVB transport streams when encoders use either [[Spectral band replication|SBR]] or [[parametric stereo]] AAC extensions. However, it is restricted to only a single non-multiplexed AAC stream. This format is also referred to as a Low Overhead Audio Transport Multiplex (LATM), which is just an interleaved multiple stream version of a LOAS.<ref name="aes2003"/>

== Encoders and decoders ==

=== Tools ===

==== Apple AAC ====
[[Apple Inc.|Apple]]'s AAC encoder was first part of the [[QuickTime]] media framework but is now at Audio Toolbox.

====FAAC and FAAD2====
{{Main|FAAC}}

FAAC and FAAD2 stand for Freeware Advanced Audio Coder and Decoder 2 respectively. FAAC supports audio object types LC, Main and LTP.<ref>{{cite web |title=FAAC |url=http://www.audiocoding.com/faac.html |url-status=live |archive-url=https://web.archive.org/web/20091211205237/http://www.audiocoding.com/faac.html |archive-date=2009-12-11 |access-date=2009-11-03 |website=AudioCoding.com}}</ref> FAAD2 supports audio object types LC, Main, LTP, SBR and PS.<ref>{{cite web |title=FAAD2 |url=http://www.audiocoding.com/faad2.html |url-status=live |archive-url=https://web.archive.org/web/20091211215311/http://www.audiocoding.com/faad2.html |archive-date=2009-12-11 |access-date=2009-11-03 |website=AudioCoding.com}}</ref> Although FAAD2 is [[free software]], FAAC is not free software.

====Fraunhofer FDK AAC====
{{Main|Fraunhofer FDK AAC}}

A [[Fraunhofer IIS|Fraunhofer]]-authored open-source encoder/decoder included in [[Android (operating system)|Android]] has been ported to other platforms. FFmpeg's native AAC encoder does not support HE-AAC and HE-AACv2, but GPL 2.0+ of ffmpeg is not compatible with FDK AAC, hence ffmpeg with libfdk-aac is not redistributable. The QAAC encoder that is using Apple's Core Media Audio is still higher quality than FDK.

====FFmpeg and Libav====
{{See also|FAAC#Alternatives for AAC encoding in Unix-like operating systems}}

The native AAC encoder created in [[FFmpeg]]'s [[libavcodec]], and forked with [[Libav]], was considered experimental and poor. A significant amount of work was done for the 3.0 release of FFmpeg (February 2016) to make its version usable and competitive with the rest of the AAC encoders.<ref>{{cite web |title=December 5th, 2015, The native FFmpeg AAC encoder is now stable! |url=https://ffmpeg.org/index.html#aac_encoder_stable |url-status=live |archive-url=https://web.archive.org/web/20160716124052/http://ffmpeg.org/index.html#aac_encoder_stable |archive-date=16 July 2016 |access-date=26 June 2016 |website=ffmpeg.org}}</ref> Libav has not merged this work and continues to use the older version of the AAC encoder. These encoders are [[LGPL]]-licensed open-source and can be built for any platform that the FFmpeg or Libav frameworks can be built.

Both FFmpeg and Libav can use the [[Fraunhofer FDK AAC]] library via libfdk-aac, and while the FFmpeg native encoder has become stable and good enough for common use, FDK is still considered the highest quality encoder available for use with FFmpeg.<ref name="ffmpegdoc">{{cite web |title=FFmpeg AAC Encoding Guide |url=https://trac.ffmpeg.org/wiki/Encode/AAC#fdk_aac |url-status=live |archive-url=https://web.archive.org/web/20160417000546/http://trac.ffmpeg.org/wiki/Encode/AAC#fdk_aac |archive-date=17 April 2016 |access-date=11 April 2016 |quote=Which encoder provides the best quality? ... the likely answer is: libfdk_aac}}</ref> Libav also recommends using FDK AAC if it is available.<ref>{{cite web |title=Libav Wiki - Encoding AAC |url=https://wiki.libav.org/Encoding/aac |url-status=dead |archive-url=https://web.archive.org/web/20160420213129/https://wiki.libav.org/Encoding/aac |archive-date=2016-04-20 |access-date=11 April 2016}}</ref> FFmpeg 4.4 and above can also use the Apple audiotoolbox encoder.<ref name="ffmpegdoc" />

Although the native AAC encoder only produces AAC-LC, ffmpeg's native decoder is able to deal with a wide range of input formats.

====Nero Digital Audio====
In May 2006, [[Nero AG]] released an AAC encoding tool free of charge, ''Nero Digital Audio'' (the AAC codec portion has become [[Nero AAC Codec]]),<ref>{{cite web |title=Nero Platinum 2018 Suite - Award-winning all-rounder |url=http://www.nero.com/eng/downloads-nerodigital-nero-aac-codec.php |url-status=live |archive-url=https://web.archive.org/web/20121214011559/http://www.nero.com/eng/downloads-nerodigital-nero-aac-codec.php |archive-date=14 December 2012 |access-date=8 May 2018 |website=Nero AG}}</ref> which is capable of encoding LC-AAC, HE-AAC and HE-AAC v2 streams. The tool is a command-line interface tool only. A separate utility is also included to decode to PCM [[WAV]].

Various tools including the [[foobar2000]] audio player and [[MediaCoder]] can provide a [[GUI]] for this encoder.

=== Media players ===
{{More citations needed section|date=September 2017}}
Almost all current computer media players include built-in decoders for AAC, or can utilize a [[Library (computer science)|library]] to decode it. On [[Microsoft Windows]], [[DirectShow]] can be used this way with the corresponding filters to enable AAC playback in any [[DirectShow]] based player. [[Mac OS X]] supports AAC via the [[QuickTime]] libraries. [[Adobe Flash Player]], since version 9 update 3, can also play back AAC streams.<ref>{{cite web |title=Statistics - Adobe Flash runtimes |url=https://www.adobe.com/products/player_census/flashplayer/version_penetration.html |url-status=live |archive-url=https://web.archive.org/web/20111002084030/http://www.adobe.com/products/player_census/flashplayer/version_penetration.html |archive-date=2 October 2011 |access-date=8 May 2018 |website=www.adobe.com}}</ref><ref>{{cite web |date=2007-12-04 |title=Adobe Delivers Flash Player 9 with H.264 Video Support |url=https://www.adobe.com/aboutadobe/pressroom/pressreleases/200712/120407adobemoviestar.html |url-status=dead |archive-url=https://web.archive.org/web/20140821183435/http://www.adobe.com/aboutadobe/pressroom/pressreleases/200712/120407adobemoviestar.html |archive-date=2014-08-21 |access-date=2014-08-20 |website=Adobe press release}}</ref> Since Flash Player is also a browser plugin, it can play AAC files through a browser as well.

The [[Rockbox]] [[Open-source software|open source]] [[firmware]] (available for multiple portable players) also offers support for AAC to varying degrees, depending on the model of player and the AAC profile.

Optional iPod support (playback of unprotected AAC files) for the [[Xbox 360]] is available as a free download from [[Xbox Live]].<ref>{{Cite web |title=Xbox.com &#124; System Use - Use an Apple iPod with Xbox 360<!-- Bot generated title --> |url=http://www.xbox.com/en-US/support/systemuse/xbox360/digitalmedia/ipod.htm |url-status=dead |archive-url=https://web.archive.org/web/20070408201732/http://www.xbox.com/en-US/support/systemuse/xbox360/digitalmedia/ipod.htm |archive-date=April 8, 2007}}</ref>

The following is a non-comprehensive list of other software player applications:
*[[3ivx|3ivx MPEG-4]]: a suite of DirectShow and QuickTime plugins which support AAC encoding or AAC/ HE-AAC decoding in any DirectShow application
*[[CorePlayer]]: also supports LC and HE AAC
*[[ffdshow]]: a free [[Open-source software|open source]] [[DirectShow]] filter for [[Microsoft Windows]] that uses FAAD2 to support AAC decoding
*[[foobar2000]]: a [[freeware]] [[audio player (software)|audio player]] for [[Windows]] that supports LC and HE AAC
*[[KMPlayer]]
*[[MediaMonkey]]
*[[AIMP]]
*[[Media Player Classic#Forks|Media Player Classic Home Cinema]]
* [[mp3tag]]
*[[MPlayer]] or [[xine]]: often used as AAC decoders on [[Linux]] or [[Macintosh]]
*[[MusicBee]]: an advanced music manager and player that also supports encoding and ripping through a plugin
*[[RealPlayer]]: includes [[RealNetworks]]' RealAudio 10 AAC encoder
*[[Songbird (software)|Songbird]]: supports AAC on Windows, Linux and [[Mac OS X]], including the DRM rights management encoding used for purchased music from the iTunes Store, with a plug-in
*[[Sonicstage|Sony SonicStage]]
*[[VLC media player]]: supports playback and encoding of MP4 and raw AAC files
*[[Winamp]] for Windows: includes an AAC encoder that supports LC and HE AAC
*[[Windows Media Player 12]]: released with [[Windows 7]], supports playback of AAC files natively
*Another Real: [[Rhapsody (online music service)|Rhapsody]] supports the RealAudio AAC codec, in addition to offering subscription tracks encoded with AAC
*[[XBMC]]: supports AAC (both LC and HE).
*[[XMMS]]: supports MP4 playback using a plugin provided by the faad2 library
Some of these players (e.g., foobar2000, Winamp, and VLC) also support the decoding of ADTS (Audio Data Transport Stream) using the [[SHOUTcast]] protocol. Plug-ins for Winamp and foobar2000 enable the creation of such streams.

===Use in HDTV broadcasting===

====Japanese ISDB-T====
In December 2003, Japan started broadcasting terrestrial DTV [[ISDB-T]] standard that implements MPEG-2 video and MPEG-2 AAC audio.
In April 2006 Japan started broadcasting the ISDB-T mobile sub-program, called 1seg, that was the first implementation of video H.264/AVC with audio HE-AAC in Terrestrial HDTV broadcasting service on the planet.

====International ISDB-Tb====
In December 2007, Brazil started broadcasting terrestrial DTV standard called International [[ISDB-Tb]] that implements video coding H.264/AVC with audio AAC-LC on main program (single or multi) and video H.264/AVC with audio HE-AACv2 in the 1seg mobile sub-program.

====DVB====
The [[ETSI]], the standards governing body for the [[Digital Video Broadcasting|DVB suite]], supports AAC, HE-AAC and HE-AAC v2 audio coding in DVB applications since at least 2004.<ref>ETSI TS 101 154 v1.5.1: Specification for the use of Video and Audio Coding in Broadcasting Applications based on the [[MPEG transport stream]]</ref> DVB broadcasts which use the [[H.264]] compression for video normally use HE-AAC for audio.{{Citation needed|date=January 2010}}

===Hardware===
{{Update section|date=April 2025}}

====iTunes and iPod====
In April 2003, [[Apple Inc.|Apple]] brought mainstream attention to AAC by announcing that its [[iTunes]] and [[iPod]] products would support songs in MPEG-4 AAC format (via a [[firmware]] update for older iPods). Customers could download music in a closed-source [[digital rights management]] (DRM)-restricted form of 128&nbsp;kbit/s AAC (see [[FairPlay]]) via the [[iTunes Store]] or create files without DRM from their own CDs using iTunes. In later years, Apple began offering music videos and movies, which also use AAC for audio encoding.

On May 29, 2007, Apple began selling songs and music videos from participating record labels at higher bitrate (256&nbsp;kbit/s cVBR) and free of DRM, a format dubbed "iTunes Plus" . These files mostly adhere to the AAC standard and are playable on many non-Apple products but they do include custom iTunes information such as [[album artwork]] and a purchase receipt, so as to identify the customer in case the file is leaked out onto [[peer-to-peer]] networks. It is possible, however, to remove these custom tags to restore interoperability with players that conform strictly to the AAC specification. As of January 6, 2009, nearly all music on the USA regioned iTunes Store became DRM-free, with the remainder becoming DRM-free by the end of March 2009.<ref>
{{cite web
| url=http://www.macworld.com/article/137946/2009/01/itunestore.html
| title=iTunes Store goes DRM-free
| access-date=2009-02-10
| last=Cohen
| first=Peter
| date=2010-05-27
| work=Macworld
| publisher=Mac Publishing
| archive-url= https://web.archive.org/web/20090218092311/http://www.macworld.com/article/137946/2009/01/itunestore.html| archive-date= 18 February 2009 | url-status= live}}</ref>

iTunes offers a "Variable Bit Rate" encoding option which encodes AAC tracks in the [[Average bitrate|Constrained Variable Bitrate]] scheme (a less strict variant of ABR encoding); the underlying QuickTime API does offer a true VBR encoding profile however.<ref>{{cite web
| url=https://wiki.hydrogenaud.io/index.php?title=Apple_AAC#afconvert
| title=Apple AAC
| access-date=2021-11-22
| publisher=[[Hydrogenaudio]]
| url-status= live|archive-url=https://web.archive.org/web/20211123040120/https://wiki.hydrogenaud.io/index.php?title=Apple_AAC#afconvert|archive-date=2021-11-23}}</ref>

As of September 2009, Apple has added support for [[HE-AAC]] (which is fully part of the MP4 standard) only for radio streams, not file playback, and iTunes still lacks support for true VBR encoding.

==== Other portable players ====
*[[Archos]]
*[[Cowon]] (unofficially supported on some models)
*[[Creative Zen]] Portable
*[[Fiio]] (all current models)
*[[Nintendo 3DS]]
*[[Nintendo DSi]]
*[[Philips GoGear]] Muse
*[[PlayStation Portable]] (PSP) with firmware 2.0 or greater
*[[Samsung YEPP]]
*[[SanDisk Sansa]] (some models)
*[[Walkman]]
*[[Zune]]
*Any portable player that fully supports the [[Rockbox]] third party firmware

====Mobile phones====
For a number of years, many mobile phones from manufacturers such as [[Nokia]], [[Motorola]], [[Samsung]], [[Sony Ericsson]], [[BenQ-Siemens]] and [[Philips]] have supported AAC playback. The first such phone was the [[Nokia 5510]] released in 2002 which also plays MP3s. However, this phone was a commercial failure{{citation needed|date=September 2014}} and such phones with integrated music players did not gain mainstream popularity until 2005 when the trend of having AAC as well as MP3 support continued. Most new smartphones and music-themed phones support playback of these formats.
* '''[[Sony Ericsson]]''' phones support various AAC formats in MP4 container. AAC-LC is supported in all phones beginning with [[Sony Ericsson K700|K700]], phones beginning with [[W550]] have support of HE-AAC. The latest devices such as the [[P990]], [[K610]], [[W890i]] and later support HE-AAC v2.
* '''[[Nokia XpressMusic]]''' and other new generation Nokia multimedia phones like N- and E-Series also support AAC format in LC, HE, M4A and HEv2 profiles. These also supports playing LTP-encoded AAC audio.
* '''[[BlackBerry]]''' phones running the [[BlackBerry 10]] operating system support AAC playback natively. Select previous generation [[BlackBerry OS]] devices also support AAC.
* '''[[bada OS]]'''
* '''[[Apple Inc.|Apple]]'s [[iPhone]]''' supports AAC and FairPlay protected AAC files formerly used as the default encoding format in the iTunes Store until the [[FairPlay#Announcement of FairPlay restrictions removal|removal of DRM restrictions in March 2009]].
* '''[[Android (operating system)|Android]]''' 2.3<ref>{{cite web|url=http://developer.android.com/about/versions/android-2.3-highlights.html|title=Gingerbread - Android Developers|website=Android Developers|access-date=8 May 2018|url-status=live|archive-url=https://web.archive.org/web/20171229061610/https://developer.android.com/about/versions/android-2.3-highlights.html|archive-date=29 December 2017}}</ref> and later supports AAC-LC, HE-AAC and HE-AAC v2 in MP4 or M4A containers along with several other audio formats. Android 3.1 and later supports raw ADTS files. Android 4.1 can encode AAC.<ref>{{cite web|url=http://developer.android.com/guide/appendix/media-formats.html|title=Supported media formats - Android Developers|website=Android Developers|access-date=8 May 2018|url-status=live|archive-url=https://web.archive.org/web/20120311121312/http://developer.android.com/guide/appendix/media-formats.html|archive-date=11 March 2012}}</ref>
* '''[[WebOS]]''' by HP/Palm supports AAC, AAC+, eAAC+, and .m4a containers in its native music player as well as several third-party players. However, it does not support Apple's FairPlay DRM files downloaded from iTunes.<ref>{{cite web|website=Palm USA|title=Palm Pre Phone / Features, Details|url=http://www.palm.com/us/products/phones/pre/#techspecs|url-status=dead|archive-url=https://web.archive.org/web/20110524144931/http://www.palm.com/us/products/phones/pre/#techspecs|archive-date=2011-05-24 }}</ref>
* '''[[Windows Phone]]'''<nowiki/>'s [[Silverlight]] runtime supports AAC-LC, HE-AAC and HE-AAC v2 decoding.

====Other devices====
*'''[[Apple Inc.|Apple]]'s [[iPad]]''': Supports AAC and FairPlay protected AAC files used as the default encoding format in the iTunes Store
*'''[[Palm OS]] [[Personal digital assistant|PDAs]]''': Many Palm OS based PDAs and smartphones can play AAC and HE-AAC with the 3rd party software [[Pocket Tunes]]. Version 4.0, released in December 2006, added support for native AAC and HE-AAC files. The AAC codec for [[TCPMP]], a popular video player, was withdrawn after version 0.66 due to patent issues, but can still be downloaded from sites other than corecodec.org. CorePlayer, the commercial follow-on to TCPMP, includes AAC support. Other Palm OS programs supporting AAC include Kinoma Player and AeroPlayer.
*'''[[Windows Mobile]]''': Supports AAC either by the native [[Windows Media Player]] or by third-party products (TCPMP, CorePlayer){{Citation needed|date=January 2010}}
*'''[[Epson]]''': Supports AAC playback in the [[Epson P-2000|P-2000]] and [[Epson P-4000|P-4000]] Multimedia/Photo Storage Viewers
*'''[[Sony Reader]]''': plays M4A files containing AAC, and displays metadata created by iTunes. Other Sony products, including the A and E series Network Walkmans, support AAC with firmware updates (released May 2006) while the S series supports it out of the box.
*'''[[Sonos]] Digital Media Player''': supports playback of AAC files
*'''Barnes & Noble [[Nook Color]]''': supports playback of AAC encoded files
*'''Roku [[SoundBridge]]''': a network audio player, supports playback of AAC encoded files
*'''[[Squeezebox (network music player)|Squeezebox]]''': network audio player (made by [[Slim Devices]], a [[Logitech]] company) that supports playback of AAC files
*'''[[PlayStation 3]]''': supports encoding and decoding of AAC files
*'''[[Xbox 360]]''': supports streaming of AAC through the Zune software, and of supported iPods connected through the USB port
*'''[[Wii]]''': supports AAC files through version 1.1 of the [[Photo Channel]] as of December 11, 2007. All AAC profiles and bitrates are supported as long as it is in the .m4a file extension. The 1.1 update removed MP3 compatibility, but according to Nintendo, users who have installed this may freely downgrade to the old version if they wish.<ref>{{cite web|url=https://www.nintendo.com/consumer/systems/wii/en_na/channelsPhoto.jsp#photo1.1|title=Nintendo - Customer Service - Wii - Photo Channel<!-- Bot generated title -->|website=nintendo.com|access-date=8 May 2018|url-status=live|archive-url=https://web.archive.org/web/20170505150346/https://www.nintendo.com/consumer/systems/wii/en_na/channelsPhoto.jsp#photo1.1|archive-date=5 May 2017}}</ref>
*'''[[Livescribe]] Pulse and Echo Smartpens''': record and store audio in AAC format. The audio files can be replayed using the pen's integrated speaker, attached headphones, or on a computer using the Livescribe Desktop software. The AAC files are stored in the user's "My Documents" folder of the Windows OS and can be distributed and played without specialized hardware or software from Livescribe.
*'''Google [[Chromecast]]''': supports playback of LC-AAC and HE-AAC audio<ref>{{cite web |url=https://developers.google.com/cast/docs/media |title=Supported Media for Google Cast |access-date=2015-09-22 |url-status=live |archive-url=https://web.archive.org/web/20150923004649/https://developers.google.com/cast/docs/media |archive-date=2015-09-23 }} | Supported Media for Google Cast</ref>

==See also==
* [[Comparison of audio coding formats]]
* [[HE-AAC]] and [[AAC-LD]]
* [[MPEG-4 Part 14]] (container format)
* [[Vorbis]] and [[Opus (audio codec)|Opus]] – [[royalty-free]] lossy competitors to AAC
* [[Windows Media Audio]] – a competing lossy codec
* [[E-AC-3|Dolby E-AC-3]] – another lossy compression scheme

==Notes==
{{notelist}}

==References==
{{Reflist|30em}}

==External links==
*[https://www.iis.fraunhofer.de/en/bf/amm/produkte/audiocodec.html Fraunhofer audio codecs]
*[https://www.audiocoding.com/ AudioCoding.com] {{Webarchive|url=https://web.archive.org/web/20060825230111/https://www.audiocoding.com/ |date=2006-08-25 }} – home of FAAC and FAAD2
*[https://mpeg.chiariglione.org/ Official MPEG web site]
*[[commons:File:AAC profiles.svg|AAC improvements and extensions (2004)]]
*{{IETF RFC|3016}} - RTP Payload Format for MPEG-4 Audio/Visual Streams
*{{IETF RFC|3640}} - RTP Payload Format for Transport of MPEG-4 Elementary Streams
*{{IETF RFC|4281}} - The Codecs Parameter for "Bucket" Media Types
*{{IETF RFC|4337}} - MIME Type Registration for MPEG-4
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[[Category:Audio codecs]]
[[Category:Lossy compression algorithms]]
[[Category:MPEG]]
[[Category:Open standards covered by patents]]