Advanced Audio Coding

Advanced Audio Coding
ITunes-aacp.png
iTunes DRM-restricted AAC file icon
Filename extension .m4a, .m4b, .m4p, .m4v, .m4r, .3gp, .mp4, .aac
Internet media type audio/aac, audio/aacp, audio/3gpp, audio/3gpp2, audio/mp4, audio/MP4A-LATM, audio/mpeg4-generic
Initial release 1997 (1997)[1]
Type of format Audio compression format, Lossy compression
Standard(s) ISO/IEC 13818-7,
ISO/IEC 14496-3

Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio. Designed to be the successor of the MP3 format, AAC generally achieves better sound quality than MP3 at similar bit rates.[2]

AAC has been standardized by ISO and IEC, as part of the MPEG-2 and MPEG-4 specifications.[3][4] The MPEG-2 standard contains several audio coding methods, including the MP3 coding scheme. AAC is able to include 48 full-bandwidth (up to 96 kHz) audio channels in one stream plus 16 low frequency effects (LFE, limited to 120 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 kbit/s in joint stereo mode; however, hi-fi transparency demands data rates of at least 128 kbit/s (VBR). The MPEG-2 audio tests showed that AAC meets the requirements referred to as "transparent" for the ITU at 128 kbit/s for stereo, and 320 kbit/s for 5.1 audio.

AAC is also the default or standard audio format for: Apple's iPhone, iPod, iPad, Nintendo DSi, iTunes, DivX Plus Web Player, Sony's PlayStation 3 and is supported by Sony's PlayStation Portable, latest generation of Sony Walkman, phones from Sony Ericsson, the latest S40 and S60 models from Nokia, Android based phones, Nintendo's Wii (with the Photo Channel 1.1 update installed for Wii consoles purchased before late 2007), and the MPEG-4 video standard.

"High-Efficiency AAC" is part of digital radio standards like DAB+ and Digital Radio Mondiale, and mobile television standards DVB-H and ATSC-M/H.

Contents

History

AAC was developed with the cooperation and contributions of companies including AT&T Bell Laboratories, Fraunhofer IIS, Dolby, Sony Corporation and Nokia, and was officially declared an international standard by the Moving Picture Experts Group in April 1997. MPEG-2 AAC-LC profile consists of a base format very much like AT&T's Perceptual Audio Coding (PAC) coding format,[5][6][7] with the addition of temporal noise shaping (TNS),[8] the Dolby Kaiser Window described below, a nonuniform quantizer, and a reworking of the bitstream format to handle up to 16 stereo, 16 mono, 16 LFE, 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 SSR uses a 4-band PQMF filterbank, with four shorter filterbanks following, in order to allow for scalable sampling rates.

Standardization

It is specified both as Part 7 of the MPEG-2 standard, and Subpart 4 in Part 3 of the MPEG-4 standard.[9] As such, it can be referred to as MPEG-2 Part 7 and MPEG-4 Part 3 AAC depending on its implementation, however it is most often referred to as MPEG-2 AAC, MPEG-4 AAC, or AAC for short.

AAC was first specified in the standard MPEG-2 Part 7 (known formally as ISO/IEC 13818-7:1997) in 1997 as a new "part" (distinct from ISO/IEC 13818-3, a.k.a. MPEG-2 BC - backwards compatible[10][11]) in the MPEG-2 family of international standards. It is known as MPEG-2 NBC (Non-Backward Compatible), because it is not compatible with the MPEG-1 Audio formats (MP3, MP2, MP1).[10][12][13][14] It defined three profiles: Low complexity profile (AAC LC), Main profile (AAC Main) and Scalable sampling rate profile (AAC SSR).

It was updated in MPEG-4 Part 3 (MPEG-4 Audio) (known formally as ISO/IEC 14496-3:1999) in 1999. The MPEG-4 Part 3 standard also defined usage of other audio compression formats (a.k.a. Audio Object Types), such as TwinVQ, CELP, HVXC, Text-To-Speech Interface, Structured Audio and others. A notable addition in this version of the AAC standard is Perceptual Noise Substitution (PNS). MPEG-4 Audio is defined in a way that it remains backwards compatible to MPEG-2 AAC.[15] The MPEG-2 Part 7 profiles - 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 (using the same names AAC LC, AAC Main and AAC SSR).[16] 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).[17][18] The reference software for MPEG-4 Part 3 is specified in MPEG-4 Part 4 and the conformance bit-streams are specified in MPEG-4 Part 5.

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 Line plus Noise and Error Resilient (ER) versions of object types.[19][20][21] It also defined four new audio profiles: High Quality Audio Profile, Low Delay Audio Profile, Natural Audio Profile and Mobile Audio Internetworking Profile.[22]

The HE-AAC Profile (AAC LC with SBR) and AAC Profile (AAC LC) were first standardized in ISO/IEC 14496-3:2001/Amd 1:2003.[23] The HE-AAC v2 Profile (AAC LC with SBR and Parametric Stereo) was first specified in ISO/IEC 14496-3:2005/Amd 2:2006.[24][25][26] The Parametric Stereo audio object type used in HE-AAC v2 was first defined in ISO/IEC 14496-3:2001/Amd 2:2004.[27][28][29]

The current version of the AAC standard is defined in ISO/IEC 14496-3:2009.[30]

AAC+ v2 is also standardized by ETSI (European Telecommunications Standards Institute) as TS 102005.[27]

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).

Blind tests show that AAC demonstrates greater sound quality and transparency than MP3 for files coded at the same bit rate.[2]

Improvements include:

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. However, in terms of whether AAC is better than MP3, the advantages of AAC are not entirely decisive, and the MP3 specification, although antiquated, has proven surprisingly robust in spite of considerable flaws. AAC and HE-AAC are better than MP3 at low bit rates (typically less than 128 kilobits per second). This is especially true at very low bit rates where the superior stereo coding, pure MDCT, and more optimal transform window sizes leave MP3 unable to compete. However, as bit rate increases, the efficiency of an audio format becomes less important relative to the efficiency of the encoder's implementation, and the intrinsic advantage AAC holds over MP3 no longer dominates audio quality.

How AAC works

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.

  1. Signal components that are perceptually irrelevant are discarded;
  2. Redundancies in the coded audio signal are eliminated.

The actual encoding process consists of the following steps:

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 bitrate speech coding to high-quality audio coding and music synthesis.

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).

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[31][1]:

The MPEG-4 Part 3 standard (MPEG-4 Audio) defined various new compression tools (a.k.a. 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.[16] Here is a list of some audio profiles defined in the MPEG-4 standard:[24][32]

(One of many improvements in MPEG-4 Audio is the Object Type - Long Term Prediction (LTP), which is an improvement of the Main profile using a forward predictor with lower computational complexity.[15])

Depending on the AAC profile and the MP3 encoder, 96 kbit/s AAC can give nearly the same or better perceptual quality as 128 kbit/s MP3.[33]

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.

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

AAC Low Delay

The MPEG-4 Low Delay Audio Coder (AAC-LD) is designed to combine the advantages of perceptual audio coding with the low delay necessary for two-way communication. It is closely derived from the MPEG-2 Advanced Audio Coding (AAC) format.

Licensing and patents

No licenses or payments are required to be able to stream or distribute content in AAC format.[34] This reason alone makes AAC a much more attractive format to distribute content than MP3, particularly for streaming content (such as Internet radio).

However, a patent license is required for all manufacturers or developers of AAC codecs.[35] It is for this reason FOSS implementations such as FFmpeg and FAAD are distributed in source form only, in order to avoid patent infringement. (See below under Products that support AAC, Software.)

Extensions and improvements

Some extensions have been added to the first AAC standard (defined in MPEG-2 Part 7 in 1997):

Container formats

In addition to the MP4, 3GP and other ISO base media file format-based container formats for storage, AAC audio data may be packaged in a more basic format called Audio Data Interchange Format (ADIF),[37] consisting of a single header followed by the raw AAC audio data blocks.[38] Alternatively, it may be packaged in a streaming format called Audio Data Transport Stream (ADTS), consisting of a series of frames, each frame having a header followed by the AAC audio data.[37] Both formats 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.[37] Two more formats are defined in MPEG-4 Part 3: Low-overhead MPEG-4 Audio Transport Multiplex (LATM), which provides a way to combine separate audio payloads, and Low Overhead Audio Stream (LOAS), a self-synchronizing streaming format.[37]

Products that support AAC

HDTV Standards

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 DVB suite, supports AAC, HE-AAC and HE-AAC v2 audio coding in DVB applications since at least 2004.[39] DVB broadcasts which use the h.264 codec for video normally use the HE-AAC codec for audio.

Hardware

iTunes and iPod

In April 2003, Apple Computer 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 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 free of DRM from participating record labels. 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 iTunes Store became DRM-free, with the remainder becoming DRM-free by the end of March 2009.[40]

iTunes supports a "Variable bit rate" (VBR) encoding option which encodes AAC tracks in an "Average bit rate" (ABR) scheme. As of September 2009, Apple has added support for HE-AAC (which is fully part of the MP4 standard) but iTunes still lacks support for true VBR encoding. The underlying QuickTime API does offer a true VBR encoding profile however.

Other portable players

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 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.

Other devices

Software

Flash Player

A very common program supporting AAC playback is Flash player, version 9, update 3 and above.[42][43] Since flash player is also a browser plugin, it can play AAC files through a browser as well.

The Rockbox 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.[44]

Other software media players

Almost all current computer media players include built-in decoders for AAC, or can utilize a library to decode it. On Microsoft Windows, DirectShow can be utilized this way with the corresponding filters to enable AAC playback in any DirectShow based player. Mac OS X supports AAC via the QuickTime libraries. Software player applications of particular note include:

Some of these players (e.g., foobar2000, Winamp, and VLC) also support the decoding of ADTS (Audio Data Transport Stream) or MP4-contained AAC streamed over HTTP using the SHOUTcast protocol. Plug-ins for Winamp and foobar2000 enable the creation of such streams.

Nero Digital Audio

In May 2006, Nero AG released an AAC encoding tool free of charge, Nero Digital Audio (Nero AAC Codec),[45] which is capable of encoding LC-AAC, HE-AAC and HE-AAC v2 streams. The tool is a Command Line Interface tool only, and a separate utility is included to decode to PCM WAV.

Various tools including the foobar2000 audio player, MediaCoder, MeGUI encoding front end and dBpoweramp can provide a GUI for the encoder.

FAAC and FAAD2

FAAC and FAAD2 stand for Freeware Advanced Audio Coder and Decoder 2 respectively. FAAC supports audio object types LC, Main and LTP.[46] FAAD2 supports audio object types LC, Main, LTP, SBR and PS.[47]

See also

Notes

  1. ↑ 1.0 1.1 ISO (1997). "ISO/IEC 13818-7:1997, Information technology -- Generic coding of moving pictures and associated audio information -- Part 7: Advanced Audio Coding (AAC)". http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=25040. Retrieved 2010-07-18. 
  2. ↑ 2.0 2.1 Brandenburg, Karlheinz (1999). "MP3 and AAC Explained". http://www.telos-systems.com/techtalk/hosted/Brandenburg_mp3_aac.pdf 
  3. ↑ ISO (2006) ISO/IEC 13818-7:2006 - Information technology -- Generic coding of moving pictures and associated audio information -- Part 7: Advanced Audio Coding (AAC), Retrieved on 2009-08-06
  4. ↑ ISO (2006) ISO/IEC 14496-3:2005 - Information technology -- Coding of audio-visual objects -- Part 3: Audio, Retrieved on 2009-08-06
  5. ↑ Johnston, J. D. and Ferreira, A. J., "Sum-difference stereo transform coding", ICASSP '92, March 1992, pp. II-569-572.
  6. ↑ Sinha, D. and Johnston, J. D., "Audio compression at low bit rates using a signal adaptive switched filterbank", IEEE ASSP, 1996, pp. 1053-1057.
  7. ↑ 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.
  8. ↑ 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
  9. ↑ ISO/IEC (1 September 2009) (PDF). ISO/IEC 14496-3:2009 - Information technology -- Coding of audio-visual objects -- Part 3: Audio. IEC. http://webstore.iec.ch/preview/info_isoiec14496-3%7Bed4.0%7Den.pdf. Retrieved 2009-10-07 
  10. ↑ 10.0 10.1 MPEG.ORG. "AAC". http://www.mpeg.org/MPEG/audio/aac.html. Retrieved 2009-10-28. 
  11. ↑ ISO (15 January 2006). "ISO/IEC 13818-7, Fourth edition, Part 7 - Advanced Audio Coding (AAC)" (PDF). http://webstore.iec.ch/preview/info_isoiec13818-7%7Bed4.0%7Den.pdf. Retrieved 2009-10-28 
  12. ↑ Gabriel Bouvigne (2003). "MPEG-2/MPEG-4 - AAC". MP3'Tech. http://www.mp3-tech.org/aac.html. Retrieved 2009-10-28. 
  13. ↑ ISO (1998-10). "MPEG Audio FAQ Version 9 - MPEG-1 and MPEG-2 BC". ISO. http://mpeg.chiariglione.org/faq/mp1-aud/mp1-aud.htm. Retrieved 2009-10-28. 
  14. ↑ ISO (1996-03). "Florence Press Release". ISO. http://mpeg.chiariglione.org/meetings/firenze/prfloren.htm. Retrieved 2009-10-28. 
  15. ↑ 15.0 15.1 15.2 Karlheinz Brandenburg, Oliver Kunz, Akihiko Sugiyama (1999). "MPEG-4 Natural Audio Coding - General Audio Coding (AAC based)". chiariglione.org. http://mpeg.chiariglione.org/tutorials/papers/icj-mpeg4-si/09-natural_audio_paper/gacoding.html. Retrieved 2009-10-06. 
  16. ↑ 16.0 16.1 Karlheinz Brandenburg, Oliver Kunz, Akihiko Sugiyama. "MPEG-4 Natural Audio Coding - Audio profiles and levels". chiariglione.org. http://mpeg.chiariglione.org/tutorials/papers/icj-mpeg4-si/09-natural_audio_paper/profiles.html. Retrieved 2009-10-06. 
  17. ↑ ISO/IEC JTC 1/SC 29/WG 11 (15 May 1998). "ISO/IEC FCD 14496-3 Subpart 1 - Draft - N2203" (PDF). ftp://ftp.tnt.uni-hannover.de/pub/MPEG/audio/mpeg4/documents/w2203/w2203.pdf. Retrieved 2009-10-07 
  18. ↑ Karlheinz Brandenburg, Oliver Kunz, Akihiko Sugiyama (15 May 1998). "MPEG-4 Natural Audio Coding - Audio profiles and levels". chiariglione.org. http://mpeg.chiariglione.org/tutorials/papers/icj-mpeg4-si/09-natural_audio_paper/profiles.html. Retrieved 2009-10-07 
  19. ↑ ISO (2000). "ISO/IEC 14496-3:1999/Amd 1:2000 - Audio extensions". ISO. http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=31568. Retrieved 2009-10-07. 
  20. ↑ ISO/IEC JTC 1/SC 29/WG 11 (1999-07). "ISO/IEC 14496-3:/Amd.1 - Final Committee Draft - MPEG-4 Audio Version 2" (PDF). ftp://ftp.tnt.uni-hannover.de/pub/MPEG/audio/mpeg4/documents/w2803/w2803_n.pdf. Retrieved 2009-10-07 
  21. ↑ Heiko Purnhagen (19 February 2000). "AES 108th Convention: MPEG-4 Version 2 Audio ­ What is it about?". Heiko Purnhagen. http://140.130.175.70/html/mpeg4/sound.media.mit.edu/mpeg4/audio/general/index.html#aes108. Retrieved 2009-10-07. 
  22. ↑ Fernando Pereira (2001-10). "Levels for Audio Profiles". MPEG Industry Forum. http://www.m4if.org/resources/profiles/audio.php. Retrieved 2009-10-15. 
  23. ↑ ISO (2003). "ISO/IEC 14496-3:2001/Amd 1:2003 - Bandwidth extension". ISO. http://www.iso.org/iso/catalogue_detail.htm?csnumber=38148. Retrieved 2009-10-07. 
  24. ↑ 24.0 24.1 ISO/IEC JTC1/SC29/WG11/N7016 (11 January 2005). "Text of ISO/IEC 14496-3:2001/FPDAM 4, Audio Lossless Coding (ALS), new audio profiles and BSAC extensions" (DOC). http://www.itscj.ipsj.or.jp/sc29/open/29view/29n6475t.doc. Retrieved 2009-10-09 
  25. ↑ ISO (2006). "Audio Lossless Coding (ALS), new audio profiles and BSAC extensions, ISO/IEC 14496-3:2005/Amd 2:2006". ISO. http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=43026. Retrieved 2009-10-13. 
  26. ↑ Mihir Mody (6 June 2005). "Audio compression gets better and more complex". Embedded.com. http://www.embedded.com/columns/specialreports/164300682?_requestid=60812. Retrieved 2009-10-13. 
  27. ↑ 27.0 27.1 http://www.codingtechnologies.com/products/assets/CT_aacPlus_whitepaper.pdf
  28. ↑ ISO (2004). "Parametric coding for high-quality audio, ISO/IEC 14496-3:2001/Amd 2:2004". ISO. http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=39382. Retrieved 2009-10-13. 
  29. ↑ 3GPP (30 September 2004). "3GPP TS 26.401 V6.0.0 (2004-09), General Audio Codec audio processing functions; Enhanced aacPlus General Audio Codec; General Description (Release 6)" (DOC). 3GPP. http://www.3gpp.org/ftp/Specs/archive/26_series/26.401/26401-600.zip. Retrieved 2009-10-13. 
  30. ↑ ISO (2009). "ISO/IEC 14496-3:2009 - Information technology -- Coding of audio-visual objects -- Part 3: Audio". ISO. http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=53943. Retrieved 2009-10-07. 
  31. ↑ ISO (15 October 2004). "ISO/IEC 13818-7, Third edition, Part 7 - Advanced Audio Coding (AAC)" (PDF). p. 32. http://jongyeob.com/moniwiki/pds/upload/13818-7.pdf. Retrieved 2009-10-19 
  32. ↑ Bernhard Grill, Stefan Geyersberger, Johannes Hilpert, Bodo Teichmann (2004-07) (PDF). Implementation of MPEG-4 Audio Components on various Platforms. Fraunhofer Gesellschaft. http://www.iis.fraunhofer.de/fhg/Images/AES5270_MPEG-4_Audio_Components_on_various_Platforms_tcm278-67534.PDF. Retrieved 2009-10-09 
  33. ↑ Apple - QuickTime - Technologies - AAC Audio
  34. ↑ Via Licensing. "AAC Licensing FAQ Q5". http://www.vialicensing.com/Licensing/AAC_FAQ.cfm?faq=5#5. 
  35. ↑ Via Licensing. "AAC License Fees". http://www.vialicensing.com/Licensing/AAC_fees.cfm. 
  36. ↑ D. Thom, H. Purnhagen, and the MPEG Audio Subgroup (1998-10). "MPEG Audio FAQ Version 9 - MPEG-4". chiariglione.org. http://mpeg.chiariglione.org/faq/mp4-aud/mp4-aud.htm. Retrieved 2009-10-06. 
  37. ↑ 37.0 37.1 37.2 37.3 Wolters, Martin; Kristofer Kjorling, Daniel Homm, Heiko Purnhagen (PDF). A closer look into MPEG-4 High Efficiency AAC. pp. 3. http://www.telos-systems.com/techtalk/hosted/HE-AAC.pdf. Retrieved 2008-07-31.  Presented at the 115th Convention of the Audio Engineering Society, 10–13 October 2003.
  38. ↑ "Advanced Audio Coding (MPEG-2), Audio Data Interchange Format". Library of Congress / National Digital Information Infrastructure and Preservation Program. 7 March 2007. http://www.digitalpreservation.gov/formats/fdd/fdd000112.shtml. Retrieved 2008-07-31. 
  39. ↑ 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
  40. ↑ Cohen, Peter (2010-05-27). "iTunes Store goes DRM-free". Macworld. Mac Publishing. http://www.macworld.com/article/137946/2009/01/itunestore.html. Retrieved 2009-02-10. 
  41. ↑ Nintendo - Customer Service | Wii - Photo Channel
  42. ↑ http://www.adobe.com/products/player_census/flashplayer/version_penetration.html
  43. ↑ http://www.adobe.com/aboutadobe/pressroom/pressreleases/200712/120407adobemoviestar.html
  44. ↑ Xbox.com | System Use - Use an Apple iPod with Xbox 360
  45. ↑ http://www.nero.com/eng/downloads-nerodigital-nero-aac-codec.php
  46. ↑ AudioCoding.com. "FAAC". http://www.audiocoding.com/faac.html. Retrieved 2009-11-03. 
  47. ↑ AudioCoding.com. "FAAD2". http://www.audiocoding.com/faad2.html. Retrieved 2009-11-03. 

please note that ref#8 has been changed to: "http://www.aacplus.net/products/assets/CT_aacPlus_whitepaper.pdf"

External links

Multimedia compression and container formats
Video compression
ISO/IEC
MJPEG · Motion JPEG 2000 · MPEG-1 · MPEG-2 (Part 2) · MPEG-4 (Part 2/ASP · Part 10/AVC) · HEVC
ITU-T
H.120 · H.261 · H.262 · H.263 · H.264 · HEVC
Others
AVS · Bink · CineForm · Cinepak · Dirac · DV · Indeo · Microsoft Video 1 · OMS Video · Pixlet · RealVideo · RTVideo · SheerVideo · Smacker · Sorenson Video & Sorenson Spark · Theora · VC-1 · VC-2 · VC-3 · VP3 · VP6 · VP7 · VP8 · WMV
Audio compression
ISO/IEC
MPEG-1 Layer III (MP3) · MPEG-1 Layer II (Multichannel) · MPEG-1 Layer I · AAC · HE-AAC · MPEG Surround · MPEG-4 ALS · MPEG-4 SLS · MPEG-4 DST · MPEG-4 HVXC · MPEG-4 CELP
ITU-T
G.711 · G.718 · G.719 · G.722 · G.722.1 · G.722.2 · G.723 · G.723.1 · G.726 · G.728 · G.729 · G.729.1
Others
AC-3 · AMR · AMR-WB · AMR-WB+ · Apple Lossless · ATRAC · CELT · DRA · DTS · EVRC · EVRC-B · FLAC · GSM-HR · GSM-FR · GSM-EFR · iLBC · iSAC · Monkey's Audio · TTA (True Audio) · MT9 · A-law · μ-law · Musepack · Nellymoser · OptimFROG · OSQ · QCELP · RealAudio · RTAudio · SD2 · SHN · SILK · Siren · SMV · Speex · SVOPC · TwinVQ · VMR-WB · Vorbis · WavPack · WMA
Image compression
ISO/IEC/ITU-T
JPEG · JPEG 2000 · JPEG XR · lossless JPEG · JBIG · JBIG2 · PNG
Others
APNG · BMP · DjVu · EXR · GIF · ICER · ILBM · MNG · PCX · PGF · TGA · QTVR · TIFF · WBMP · WebP
Media containers
ISO/IEC
MPEG-PS · MPEG-TS · ISO base media file format · MPEG-4 Part 14 · Motion JPEG 2000 · MPEG-21 Part 9
ITU-T
H.222.0 · T.802
Others
3GP and 3G2 · AMV · ASF · AIFF · AVI · AU · Bink · DivX Media Format · DPX · EVO · Flash Video · GXF · M2TS · Matroska · MXF · Ogg · QuickTime File Format · RealMedia · REDCODE RAW · RIFF · Smacker · MOD and TOD · VOB · WAV · WebM
See Compression methods for methods and Compression software implementations for codecs
High-definition (HD)
Concepts

High-definition video · High-definition television · Ultra High-definition television · High-definition audio
Analog broadcast

(All defunct): 819 line system · HD MAC · MUSE (Hi-Vision)
Digital broadcast

ATSC · DVB · ISDB · SBTVD · DMB-T/H
Audio

Dolby Digital (5.1) · MPEG-1 Layer II · PCM · LPCM · DXD · DSD · AAC
Filming and storage

HDV · DCI
HD media and
compression

Blu-ray Disc · CBHD · HD DVD · HD VMD · D-VHS · Super Audio CD · DVD-Audio · MPEG-2 · H.264 · VC-1 · MVC
Connectors

Component · HDMI · DVI · DisplayPort · VGA · HDBaseT
Deployments

List of digital television deployments by country
Resolutions
2K · 4K · 6K · 8K