Editing Advanced Audio Coding (section)

{{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"/>