Advanced Audio Coding
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Advanced Audio Coding (AAC) is an audio coding standard for lossy digital audio
compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression * Gas compression *Compression ratio, of a ...
. Designed to be the successor of the
MP3 MP3 (formally MPEG-1 Audio Layer III or MPEG-2 Audio Layer III) is a coding format for digital audio developed largely by the Fraunhofer Society in Germany, with support from other digital scientists in the United States and elsewhere. Origin ...
format, AAC generally achieves higher sound quality than MP3 encoders at the same bit rate. AAC has been standardized by
ISO ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * Iso ...
and IEC as part of the MPEG-2 and MPEG-4 specifications.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
ISO (2006

, Retrieved on 2009-08-06
Part of AAC, HE-AAC ("AAC+"), is part of
MPEG-4 Audio MPEG-4 Part 3 or MPEG-4 Audio (formally ISO/IEC 14496-3) is the third part of the ISO/IEC MPEG-4 international standard developed by Moving Picture Experts Group. It specifies audio coding methods. The first version of ISO/IEC 14496-3 was publish ...
and is adopted into digital radio standards DAB+ and Digital Radio Mondiale, and
mobile television Mobile television is television watched on a small handheld or mobile device. It includes service delivered via mobile phone networks, received free-to-air via terrestrial television stations, or via satellite broadcast. Regular broadcast stan ...
standards DVB-H and
ATSC-M/H ATSC-M/H (''Advanced Television Systems Committee - Mobile/Handheld'') is a U.S. standard for mobile digital TV that allows TV broadcasts to be received by mobile devices. ATSC-M/H is a mobile TV extension to preexisting terrestrial TV broadcasti ...
. AAC supports inclusion of 48 full-
bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...
(up to 96 kHz)
audio channel An audio signal is a representation of sound, typically using either a changing level of electrical voltage for analog signals, or a series of binary numbers for digital signals. Audio signals have frequencies in the audio frequency range of roug ...
s 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 In audio engineering, joint encoding refers to a joining of several channels of similar information during encoding in order to obtain higher quality, a smaller file size, or both. Joint stereo The term joint stereo has become prominent as the I ...
mode; however, hi-fi transparency demands data rates of at least 128 kbit/s ( VBR). Tests of MPEG-4 audio have shown 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 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 A fast Fourier transform (FFT) is an algorithm that computes the discrete Fourier transform (DFT) of a sequence, or its inverse (IDFT). Fourier analysis converts a signal from its original domain (often time or space) to a representation in the ...
. AAC is the default or standard audio format for iPhone, iPod,
iPad The iPad is a brand of iOS and iPadOS-based tablet computers that are developed by Apple Inc. The iPad was conceived before the related iPhone but the iPhone was developed and released first. Speculation about the development, operating ...
,
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, Nintendo 3DS,
YouTube Music YouTube Music is a music streaming service developed by YouTube, a subsidiary of Google. It provides a tailored interface for the service, oriented towards music streaming, allowing users to browse through songs and music videos on YouTube based ...
, Apple Music, iTunes, DivX Plus Web Player, PlayStation 4 and various
Nokia Nokia Corporation (natively Nokia Oyj, referred to as Nokia) is a Finnish multinational telecommunications, information technology, and consumer electronics corporation, established in 1865. Nokia's main headquarters are in Espoo, Finland, i ...
Series 40 Series 40, often shortened as S40, is a software platform and application user interface (UI) software on Nokia's broad range of mid-tier feature phones, as well as on some of the Vertu line of luxury phones. It was one of the world's most wi ...
phones. It is supported on a wide range of devices and software such as PlayStation Vita, Wii, digital audio players like Sony Walkman or
SanDisk Clip SanDisk has produced a number of flash memory-based digital audio and portable media players since 2005. The current range of products bear the SanDisk Clip name, a line of ultraportable digital audio players. SanDisk players were formerly market ...
, Android and BlackBerry devices, various in-dash car audio systems, and is also one of the audio formats used on the
Spotify Spotify (; ) is a proprietary Swedish audio streaming and media services provider founded on 23 April 2006 by Daniel Ek and Martin Lorentzon. It is one of the largest music streaming service providers, with over 456 million monthly active us ...
web player.


History


Background

The discrete cosine transform (DCT), a type of transform coding for lossy compression, was proposed by Nasir Ahmed in 1972, and developed by Ahmed with T. Natarajan and K. R. Rao in 1973, publishing their results in 1974. 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, following earlier work by Princen and Bradley in 1986. The
MP3 MP3 (formally MPEG-1 Audio Layer III or MPEG-2 Audio Layer III) is a coding format for digital audio developed largely by the Fraunhofer Society in Germany, with support from other digital scientists in the United States and elsewhere. Origin ...
audio coding standard introduced in 1994 used a hybrid coding algorithm that is part MDCT and part
FFT A fast Fourier transform (FFT) is an algorithm that computes the discrete Fourier transform (DFT) of a sequence, or its inverse (IDFT). Fourier analysis converts a signal from its original domain (often time or space) to a representation in the ...
. AAC uses a purely MDCT algorithm, giving it higher compression efficiency than MP3. AAC was developed with the cooperation and contributions of companies including
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial Research and development, research and scientific developm ...
,
Fraunhofer IIS The Fraunhofer Society (german: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V., lit=Fraunhofer Society for the Advancement of Applied Research) is a German research organization with 76institutes spread throughout Germany ...
, Dolby Laboratories, LG Electronics, NEC, NTT Docomo,
Panasonic formerly between 1935 and 2008 and the first incarnation of between 2008 and 2022, is a major Japanese multinational conglomerate corporation, headquartered in Kadoma, Osaka. It was founded by Kōnosuke Matsushita in 1918 as a lightbulb ...
, Sony Corporation, ETRI, JVC Kenwood, Philips,
Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washin ...
, and NTT. It 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''.


Standardization

In 1997, AAC was first introduced as ''MPEG-2 Part 7'', formally known as ''
ISO ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * 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). Therefore, MPEG-2 Part 7 is also known as ''MPEG-2 NBC'' (Non-Backward Compatible), because it is not compatible with the
MPEG-1 MPEG-1 is a standard for lossy compression of video and audio. It is designed to compress VHS-quality raw digital video and CD audio down to about 1.5 Mbit/s (26:1 and 6:1 compression ratios respectively) without excessive quality loss, making ...
audio formats ( MP1, MP2 and
MP3 MP3 (formally MPEG-1 Audio Layer III or MPEG-2 Audio Layer III) is a coding format for digital audio developed largely by the Fraunhofer Society in Germany, with support from other digital scientists in the United States and elsewhere. Origin ...
). 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, with the addition of temporal noise shaping (TNS), 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 SSR uses a 4-band 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 Part 3 or MPEG-4 Audio (formally ISO/IEC 14496-3) is the third part of the ISO/IEC MPEG-4 international standard developed by Moving Picture Experts Group. It specifies audio coding methods. The first version of ISO/IEC 14496-3 was publish ...
'', ''MPEG-4 Audio'' or ''ISO/IEC 14496-3:1999''. This update included several improvements. One of these improvements was the addition of '' Audio Object Types'' which are used to allow interoperability with a diverse range of other audio formats such as TwinVQ,
CELP Code-excited linear prediction (CELP) is a linear predictive speech coding algorithm originally proposed by Manfred R. Schroeder and Bishnu S. Atal in 1985. At the time, it provided significantly better quality than existing low bit-rate algori ...
, HVXC, Text-To-Speech Interface 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. 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). 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 Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially in ...
with MPEG-2 Part 7. 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 The MPEG-4 Low Delay Audio Coder (a.k.a. AAC Low Delay, or AAC-LD) is audio compression standard designed to combine the advantages of perceptual audio coding with the low delay necessary for two-way communication. It is closely derived from the ...
) 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. It also defined four new audio profiles: High Quality Audio Profile, Low Delay Audio Profile, Natural Audio Profile and Mobile Audio Internetworking Profile. 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. The HE-AAC v2 Profile (AAC LC with SBR and Parametric Stereo) was first specified in ISO/IEC 14496-3:2005/Amd 2:2006. The Parametric Stereo audio object type used in HE-AAC v2 was first defined in ISO/IEC 14496-3:2001/Amd 2:2004. The current version of the AAC standard is defined in ISO/IEC 14496-3:2009. AAC+ v2 is also standardized by ETSI (
European Telecommunications Standards Institute The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of information and communications. ETSI supports the development and testing of global technical standard ...
) as TS 102005. The
MPEG-4 Part 3 MPEG-4 Part 3 or MPEG-4 Audio (formally ISO/IEC 14496-3) is the third part of the ISO/IEC MPEG-4 international standard developed by Moving Picture Experts Group. It specifies audio coding methods. The first version of ISO/IEC 14496-3 was publish ...
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 ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * Iso ...
/ IEC in 11172-3 (
MPEG-1 MPEG-1 is a standard for lossy compression of video and audio. It is designed to compress VHS-quality raw digital video and CD audio down to about 1.5 Mbit/s (26:1 and 6:1 compression ratios respectively) without excessive quality loss, making ...
Audio) and 13818-3 ( MPEG-2 Audio). Blind tests in the late 1990s showed that AAC demonstrated greater sound quality and transparency than MP3 for files coded at the same bit rate. Improvements include: * more
sample rate In signal processing, sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave to a sequence of "samples". A sample is a value of the signal at a point in time and/or spa ...
s (from 8 to 96 kHz) than MP3 (16 to 48 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 rates and variable frame length. Standardized constant bit rate with bit reservoir; * higher efficiency and simpler filter bank. AAC uses a pure
MDCT The modified discrete cosine transform (MDCT) is a transform based on the type-IV discrete cosine transform (DCT-IV), with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset, where ...
(modified discrete cosine transform), rather than MP3's hybrid coding (which was part MDCT and part
FFT A fast Fourier transform (FFT) is an algorithm that computes the discrete Fourier transform (DFT) of a sequence, or its inverse (IDFT). Fourier analysis converts a signal from its original domain (often time or space) to a representation in the ...
); * higher coding efficiency for 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 signals (AAC uses a blocksize of 128 or 120 samples, allowing more accurate coding than MP3's 192 sample blocks); * possibility to use Kaiser-Bessel derived window function to eliminate
spectral leakage The Fourier transform of a function of time, s(t), is a complex-valued function of frequency, S(f), often referred to as a frequency spectrum. Any linear time-invariant operation on s(t) produces a new spectrum of the form H(f)•S(f), which cha ...
at the expense of widening the main lobe; * much better handling of audio frequencies above 16 kHz; * more flexible
joint stereo In audio engineering, joint encoding refers to a joining of several channels of similar information during encoding in order to obtain higher quality, a smaller file size, or both. Joint stereo The term joint stereo has become prominent as the I ...
(different methods can be used in different frequency ranges); * additional modules (tools) added to increase compression efficiency: 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. 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 File sharing is the practice of distributing or providing access to digital media, such as computer programs, multimedia (audio, images and video), documents or electronic books. Common methods of storage, transmission and dispersion include ...
/distribution over the internet, AAC is a strong contender due to some unwavering industry support.


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 (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 Psychoacoustics is the branch of psychophysics involving the scientific study of sound perception and audiology—how humans perceive various sounds. More specifically, it is the branch of science studying the psychological responses associated wit ...
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. 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 kbit/s) to high-quality audio coding (at 64 kbit/s per channel and higher). * AAC offers sampling frequencies between 8 kHz and 96 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 The modified discrete cosine transform (MDCT) is a transform based on the type-IV discrete cosine transform (DCT-IV), with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset, where ...
) 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: * Low Complexity (LC) – the simplest and most widely used and supported * Main Profile (Main) – like the LC profile, with the addition of backwards prediction * 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. 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. Here is a list of some audio profiles defined in the MPEG-4 standard: * 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 * 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 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.


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

The audio coding standards MPEG-4 Low Delay (
AAC-LD The MPEG-4 Low Delay Audio Coder (a.k.a. AAC Low Delay, or AAC-LD) is audio compression standard designed to combine the advantages of perceptual audio coding with the low delay necessary for two-way communication. It is closely derived from the ...
), 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. AAC-ELD is recommended by
GSMA The GSM Association (commonly referred to as 'the GSMA' or ''Global System for Mobile Communications'', originally ''Groupe Spécial Mobile'') is an industry organisation that represents the interests of mobile network operators worldwide. More ...
as super-wideband voice codec in the IMS Profile for High Definition Video Conference (HDVC) Service.


Licensing and patents

No licenses or payments are required for a user to stream or distribute content in AAC format. This reason alone might have made AAC a more attractive format to distribute content than its predecessor MP3, particularly for streaming content (such as Internet radio) depending on the use case. However, a patent license is required for all manufacturers or developers of AAC
codecs A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or d ...
. For this reason, free and open source software implementations such as
FFmpeg FFmpeg is a free and open-source software project consisting of a suite of libraries and programs for handling video, audio, and other multimedia files and streams. At its core is the command-line ffmpeg tool itself, designed for processing of vid ...
and FAAC may be distributed in
source Source may refer to: Research * Historical document * Historical source * Source (intelligence) or sub source, typically a confidential provider of non open-source intelligence * Source (journalism), a person, publication, publishing institute o ...
form only, in order to avoid patent infringement. (See below under Products that support AAC, Software.) The AAC patent holders include
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial Research and development, research and scientific developm ...
, Dolby, Fraunhofer, LG Electronics, NEC, NTT Docomo,
Panasonic formerly between 1935 and 2008 and the first incarnation of between 2008 and 2022, is a major Japanese multinational conglomerate corporation, headquartered in Kadoma, Osaka. It was founded by Kōnosuke Matsushita in 1918 as a lightbulb ...
, Sony Corporation, ETRI, JVC Kenwood, Philips,
Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washin ...
, and NTT.


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 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. * Error Resilience (ER), added in MPEG-4 Audio version 2 in 2000, used for transport over error prone channels *
AAC-LD The MPEG-4 Low Delay Audio Coder (a.k.a. AAC Low Delay, or AAC-LD) is audio compression standard designed to combine the advantages of perceptual audio coding with the low delay necessary for two-way communication. It is closely derived from the ...
(Low Delay), defined in 2000, used for real-time conversation applications * High Efficiency AAC (HE-AAC), a.k.a. aacPlus v1 or AAC+, the combination of 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 (PS) and HE-AAC; used for even lower bitrates. Defined in 2004 and 2006. * MPEG-4 Scalable To Lossless (SLS), Not yet published, can supplement an AAC stream to provide a lossless decoding option, such as in Fraunhofer IIS's "HD-AAC" product


Container formats

In addition to the MP4, 3GP and other container formats based on
ISO base media file format The ISO base media file format (ISOBMFF) is a container file format that defines a general structure for files that contain time-based multimedia data such as video and audio. It is standardized in ISO/IEC 14496-12, a.k.a. MPEG-4 Part 12, and wa ...
for file storage, AAC audio data was first packaged in a file for the MPEG-2 standard using Audio Data Interchange Format (ADIF), Presented at the 115th Convention of the Audio Engineering Society, 10–13 October 2003. consisting of a single header followed by the raw AAC audio data blocks. 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. 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. These containers, as well as a raw AAC stream, may bear the .aac file extension.
MPEG-4 Part 3 MPEG-4 Part 3 or MPEG-4 Audio (formally ISO/IEC 14496-3) is the third part of the ISO/IEC MPEG-4 international standard developed by Moving Picture Experts Group. It specifies audio coding methods. The first version of ISO/IEC 14496-3 was publish ...
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 ALS. This format is what was defined for use in DVB transport streams when encoders use either SBR or
parametric stereo Parametric Stereo (abbreviated as PS) is an audio compression algorithm used as an audio coding format for digital audio. It is considered an Audio Object Type of MPEG-4 Part 3 (MPEG-4 Audio) that serves to enhance the coding efficiency of low band ...
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.


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 ISDB-T International, or SBTVD, short for Sistema Brasileiro de Televisão Digital ( en, Brazilian Digital Television System), is a technical standard for digital television broadcast used in Brazil, Argentina, Peru, Botswana, Chile, Honduras, Ve ...
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. DVB broadcasts which use the
H.264 Advanced Video Coding (AVC), also referred to as H.264 or MPEG-4 Part 10, is a video compression standard based on block-oriented, motion-compensated coding. It is by far the most commonly used format for the recording, compression, and distr ...
compression for video normally use HE-AAC for audio.


Hardware


iTunes and iPod

In April 2003,
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, where its wild ancestor, ' ...
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 kbit/s AAC (see
FairPlay FairPlay is a digital rights management (DRM) technology developed by Apple Inc. It is built into the MP4 multimedia file format as an encrypted AAC audio layer, and was used until April 2009 by the company to protect copyrighted works sold ...
) via the
iTunes Store The iTunes Store is a digital media store operated by Apple Inc. It opened on April 28, 2003, as a result of Steve Jobs' push to open a digital marketplace for music. As of April 2020, iTunes offered 60 million songs, 2.2 million apps, 25,00 ...
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 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. iTunes offers a "Variable Bit Rate" encoding option which encodes AAC tracks in the Constrained Variable Bitrate scheme (a less strict variant of ABR encoding); the underlying QuickTime API does offer a true VBR encoding profile however. 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 Cowon Systems, Inc. (simply known as Cowon) is a South Korean consumer electronics and software corporation. The company’s initial focus was software development and microelectronics, specializing in speech synthesis and speech recognition tec ...
(unofficially supported on some models) *
Creative Zen ZEN is a series of discontinued portable media players designed and manufactured by Creative Technology Limited. The players evolved from the NOMAD brand through the NOMAD Jukebox series of music players, with the first separate "ZEN" branded mo ...
Portable * Fiio (all current models) * Nintendo 3DS *
Nintendo DSi The is a dual-screen handheld game console released by Nintendo. The console launched in Japan on November 1, 2008, and worldwide beginning in April 2009. It is the third iteration of the Nintendo DS, and its primary market rival is Sony's ...
* Philips GoGear Muse * PlayStation Portable (PSP) with firmware 2.0 or greater * Samsung YEPP *
SanDisk Sansa SanDisk has produced a number of flash memory-based digital audio and portable media players since 2005. The current range of products bear the SanDisk Clip name, a line of ultraportable digital audio players. SanDisk players were formerly market ...
(some models) * Walkman *
Zune Zune is a discontinued line of digital media products and services marketed by Microsoft from November 2006 until its discontinuation in June 2012. Zune consisted of a line of portable media players, digital media player software for Windows Per ...
*Any portable player that fully supports the
Rockbox Rockbox is a free and open-source software replacement for the OEM firmware in various forms of digital audio players (DAPs) with an original kernel. It offers an alternative to the player's operating system, in many cases without removing the or ...
third party firmware


Mobile phones

For a number of years, many mobile phones from manufacturers such as
Nokia Nokia Corporation (natively Nokia Oyj, referred to as Nokia) is a Finnish multinational telecommunications, information technology, and consumer electronics corporation, established in 1865. Nokia's main headquarters are in Espoo, Finland, i ...
,
Motorola Motorola, Inc. () was an American multinational telecommunications company based in Schaumburg, Illinois, United States. After having lost $4.3 billion from 2007 to 2009, the company split into two independent public companies, Motorol ...
,
Samsung The Samsung Group (or simply Samsung) ( ko, 삼성 ) is a South Korean multinational manufacturing conglomerate headquartered in Samsung Town, Seoul, South Korea. It comprises numerous affiliated businesses, most of them united under the ...
,
Sony Ericsson Sony Mobile Communications Inc. ( ja, ソニーモバイルコミュニケーションズ株式会社) was a multinational telecommunications company founded on October 1, 2001, as a joint venture between Sony Group Corporation and Ericsson. ...
,
BenQ-Siemens BenQ Mobile GmbH & Co. OHG was the mobile communications subsidiary of Taiwanese BenQ Corporation, selling products under the BenQ-Siemens brand. The group, based in Munich, Germany, was formed out of BenQ's acquisition of the then struggli ...
and Philips have supported AAC playback. The first such phone was the
Nokia 5510 The Nokia Nokia Corporation (natively Nokia Oyj, referred to as Nokia) is a Finnish multinational telecommunications, information technology, and consumer electronics corporation, established in 1865. Nokia's main headquarters are in Es ...
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. *
Sony Ericsson Sony Mobile Communications Inc. ( ja, ソニーモバイルコミュニケーションズ株式会社) was a multinational telecommunications company founded on October 1, 2001, as a joint venture between Sony Group Corporation and Ericsson. ...
phones support various AAC formats in MP4 container. AAC-LC is supported in all phones beginning with 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 BlackBerry OS is a discontinued proprietary mobile operating system developed by Canadian company BlackBerry Limited for its BlackBerry line of smartphone handheld devices. The operating system provides multitasking and supports specialized i ...
devices also support AAC. * bada OS *
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, where its wild ancestor, ' ...
's iPhone supports AAC and FairPlay protected AAC files formerly used as the default encoding format in the iTunes Store until the removal of DRM restrictions in March 2009. * Android 2.3 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. *
WebOS webOS, also known as LG webOS and previously known as Open webOS, HP webOS and Palm webOS, is a Linux kernel-based multitasking operating system for smart devices such as smart TVs that has also been used as a mobile operating system. Initially ...
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. * Windows Phone's Silverlight runtime supports AAC-LC, HE-AAC and HE-AAC v2 decoding.


Other devices

*
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, where its wild ancestor, ' ...
's
iPad The iPad is a brand of iOS and iPadOS-based tablet computers that are developed by Apple Inc. The iPad was conceived before the related iPhone but the iPhone was developed and released first. Speculation about the development, operating ...
: Supports AAC and FairPlay protected AAC files used as the default encoding format in the iTunes Store *
Palm OS Palm OS (also known as Garnet OS) was a mobile operating system initially developed by Palm, Inc., for personal digital assistants (PDAs) in 1996. Palm OS was designed for ease of use with a touchscreen-based graphical user interface. It is pro ...
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) *
Epson Seiko Epson Corporation, or simply known as Epson, is a Japanese multinational electronics company and one of the world's largest manufacturers of computer printers and information- and imaging-related equipment. Headquartered in Suwa, Nagano ...
: Supports AAC playback in the P-2000 and P-4000 Multimedia/Photo Storage Viewers *
Sony Reader The Sony Reader was a line of e-book readers manufactured by Sony, who produced the first commercial E Ink e-reader with the Sony Librie in 2004. It used an electronic paper display developed by E Ink Corporation, was viewable in direct sunlig ...
: 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 SoundBridge is a hardware device from Roku, Inc. designed to play internet radio or digital audio streamed across a home network, over either Wi-Fi or ethernet. SoundBridge devices directly browsed the Radio Roku guide. As of 2008 all Roku Sou ...
: a network audio player, supports playback of AAC encoded files *
Squeezebox The term squeezebox (also squeeze box, squeeze-box) is a colloquial expression referring to any musical instrument of the general class of hand-held bellows-driven free reed aerophones such as the accordion and the concertina. The term is so a ...
: network audio player (made by Slim Devices, a Logitech company) that supports playback of AAC files *
PlayStation 3 The PlayStation 3 (PS3) is a home video game console developed by Sony Computer Entertainment. The successor to the PlayStation 2, it is part of the PlayStation brand of consoles. It was first released on November 11, 2006, in Japan, November ...
: 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. This update removed MP3 compatibility, but users who have installed this may freely downgrade to the old version if they wish. *
Livescribe Livescribe is a paper-based computing platform that consists of a digital pen, digital paper, software applications, and developer tools. Central to the Livescribe platform is the ''smartpen,'' a ballpoint pen with an embedded computer and digita ...
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


Software

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 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. Since Flash Player is also a browser plugin, it can play AAC files through a browser as well. The
Rockbox Rockbox is a free and open-source software replacement for the OEM firmware in various forms of digital audio players (DAPs) with an original kernel. It offers an alternative to the player's operating system, in many cases without removing the or ...
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. The following is a non-comprehensive list of other software player applications: * 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 DirectShow filter for Microsoft Windows that uses FAAD2 to support AAC decoding * foobar2000: a freeware audio player for Windows that supports LC and HE AAC * KMPlayer *
MediaMonkey MediaMonkey is a digital media player and media library application developed by Ventis Media Inc., for organizing and playing audio on Microsoft Windows and Android operating systems. MediaMonkey for Windows (sometimes noted as MMW) include ...
*
AIMP AIMP (Artem Izmaylov Media Player) is a freeware audio player for Windows and Android, originally developed by Russian developer Artem Izmaylov ( rus, Артём Измайлов, Artyom Izmajlov).
*
Media Player Classic Home Cinema Media Player Classic (MPC), Media Player Classic - Home Cinema (MPC-HC), and Media Player Classic - Black Edition (MPC-BE) are a family of free and open-source, compact, lightweight, and customizable media players for 32-bit and 64-bit Microsoft ...
*
mp3tag Mp3tag is a metadata tag editor that supports many popular audio file formats. It is freeware for Microsoft Windows, while it costs USD $19.99 for Apple macOS in the Mac App Store. Features * Batch Tag Editing. Write ID3v1.1, ID3v2.3, ID3v2.4 ...
*
MPlayer MPlayer is a free and open-source media player software application. It is available for Linux, OS X and Microsoft Windows. Versions for OS/2, Syllable, AmigaOS, MorphOS and AROS Research Operating System are also available. A port for DOS usi ...
or
xine xine is a multimedia playback engine for Unix-like operating systems released under the GNU General Public License. xine is built around a shared library (xine-lib) that supports different frontend player applications. xine uses libraries ...
: often used as AAC decoders on
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
or
Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...
*
MusicBee MusicBee is a freeware media player for playback and organization of audio files on Microsoft Windows, built using the audio library. Features * Audio playback: MP3, AAC, M4A, MPC, OGG, FLAC, ALAC, APE, Opus, , WavPack, WMA, WAV, MI ...
: an advanced music manager and player that also supports encoding and ripping through a plugin *
RealPlayer RealPlayer, formerly RealAudio Player, RealOne Player and RealPlayer G2, is a cross-platform media player app, developed by RealNetworks. The media player is compatible with numerous container file formats of the multimedia realm, including MP3 ...
: includes
RealNetworks RealNetworks, Inc. is a provider of artificial intelligence and computer vision based products. RealNetworks was a pioneer in Internet streaming software and services. They are based in Seattle, Washington, United States. The company also p ...
' RealAudio 10 AAC encoder *
Songbird A songbird is a bird belonging to the suborder Passeri of the perching birds (Passeriformes). Another name that is sometimes seen as the scientific or vernacular name is Oscines, from Latin ''oscen'', "songbird". The Passeriformes contains 5000 ...
: supports AAC on Windows,
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
and Mac OS X , including the DRM rights management encoding used for purchased music from the iTunes Store, with a plug-in * Sony SonicStage *
VLC media player VLC media player (previously the VideoLAN Client and commonly known as simply VLC) is a free and open-source, portable, cross-platform media player software and streaming media server developed by the VideoLAN project. VLC is available for desk ...
: supports playback and encoding of MP4 and raw AAC files *
Winamp Winamp is a media player for Microsoft Windows originally developed by Justin Frankel and Dmitry Boldyrev by their company Nullsoft, which they later sold to AOL in 1999 for $80 million. It was then acquired by Radionomy in 2014. Sinc ...
for Windows: includes an AAC encoder that supports LC and HE AAC * Windows Media Player 12: released with
Windows 7 Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was released to manufacturing on July 22, 2009, and became generally available on October 22, 2009. It is the successor to Windows Vista, released nearly ...
, supports playback of AAC files natively *Another Real:
Rhapsody Rhapsody may refer to: * A work of epic poetry, or part of one, that is suitable for recitation at one time ** Rhapsode, a classical Greek professional performer of epic poetry Computer software * Rhapsody (online music service), an online m ...
supports the RealAudio AAC codec, in addition to offering subscription tracks encoded with AAC *
XBMC Kodi (formerly XBMC) is a free and open-source media player software application developed by the XBMC Foundation, a non-profit technology consortium. Kodi is available for multiple operating systems and hardware platforms, with a software 10- ...
: supports AAC (both LC and HE). *
XMMS X Multimedia System (XMMS) is an audio player for Unix-like systems released under a free software license. History XMMS was originally written as ''X11Amp'' by Peter and Mikael Alm in November 1997. The player was made to resemble Winamp, which ...
: 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.


Nero Digital Audio

In May 2006,
Nero AG Nero AG (known as Ahead Software AG until 2005) is a German computer software company that is especially well known for its CD/DVD/ BD burning suite, ''Nero Burning ROM''. The company's main product is Nero 2019, a piece of software that comp ...
released an AAC encoding tool free of charge, ''Nero Digital Audio'' (the AAC codec portion has become
Nero AAC Codec __NOTOC__ Nero AAC Codec is a set of software tools for encoding and decoding Advanced Audio Coding (AAC) format audio, and editing MPEG-4 metadata. It was developed and distributed by Nero AG, and is available at no cost for Windows and Linux f ...
), which is capable of encoding LC-AAC, HE-AAC and HE-AAC v2 streams. The tool is a
Command Line Interface A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
tool only. A separate utility is also included to decode to PCM
WAV Waveform Audio File Format (WAVE, or WAV due to its filename extension; pronounced "wave") is an audio file format standard, developed by IBM and Microsoft, for storing an audio bitstream on PCs. It is the main format used on Microsoft Wind ...
. Various tools including the foobar2000 audio player and
MediaCoder __NOTOC__ MediaCoder is a proprietary transcoding program for Microsoft Windows, developed by Stanley Huang since 2005. Features MediaCoder uses various open-source (and several proprietary) audio and video codecs to transcode media files to d ...
can provide a
GUI The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inste ...
for this 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. FAAD2 supports audio object types LC, Main, LTP, SBR and PS. Although FAAD2 is
free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, no ...
, FAAC is not free software.


Fraunhofer FDK AAC

A Fraunhofer-authored open-source encoder/decoder included in 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

The native AAC encoder created in
FFmpeg FFmpeg is a free and open-source software project consisting of a suite of libraries and programs for handling video, audio, and other multimedia files and streams. At its core is the command-line ffmpeg tool itself, designed for processing of vid ...
's
libavcodec libavcodec is a free and open-source library of codecs for encoding and decoding video and audio data. libavcodec is an integral part of many open-source multimedia applications and frameworks. The popular MPV, xine and VLC media players use ...
, and forked with
Libav Libav is an abandoned free software project, forked from FFmpeg in 2011, that contains libraries and programs for handling multimedia data. History Fork from FFmpeg The Libav project was a fork of the FFmpeg project. It was announced on M ...
, 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. Libav has not merged this work and continues to use the older version of the AAC encoder. These encoders are
LGPL The GNU Lesser General Public License (LGPL) is a free-software license published by the Free Software Foundation (FSF). The license allows developers and companies to use and integrate a software component released under the LGPL into their own ...
-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 Fraunhofer FDK AAC is an open-source library for encoding and decoding digital audio in the Advanced Audio Coding (AAC) format. Fraunhofer IIS, developed this library for Android 4.1. It supports several Audio Object Types including MPEG-2 and ...
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. Libav also recommends using FDK AAC if it is available.


See also

*
Comparison of audio coding formats The following tables compare general and technical information for a variety of audio coding formats. For listening tests comparing the perceived audio quality of audio formats and codecs, see the article Codec listening test. General informati ...
*
AAC-LD The MPEG-4 Low Delay Audio Coder (a.k.a. AAC Low Delay, or AAC-LD) is audio compression standard 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-4 Part 14 MPEG-4 Part 14 or MP4 is a digital multimedia container format most commonly used to store video and audio, but it can also be used to store other data such as subtitles and still images. Like most modern container formats, it allows stream ...
(container format) * ALAC – a lossless codec developed by
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, where its wild ancestor, ' ...
*
Vorbis Vorbis is a free and open-source software project headed by the Xiph.Org Foundation. The project produces an audio coding format and software reference encoder/decoder (codec) for lossy audio compression. Vorbis is most commonly used in conj ...
– the main open,
royalty-free Royalty-free (RF) material subject to copyright or other intellectual property rights may be used without the need to pay royalties or license fees for each use, per each copy or volume sold or some time period of use or sales. Computer standard ...
competitor to AAC and MP3 *
Opus ''Opus'' (pl. ''opera'') is a Latin word meaning "work". Italian equivalents are ''opera'' (singular) and ''opere'' (pl.). Opus or OPUS may refer to: Arts and entertainment Music * Opus number, (abbr. Op.) specifying order of (usually) publicatio ...
– an open,
royalty-free Royalty-free (RF) material subject to copyright or other intellectual property rights may be used without the need to pay royalties or license fees for each use, per each copy or volume sold or some time period of use or sales. Computer standard ...
codec for both pre-encoded and interactive use, standardized in 2012


References


External links


Fraunhofer audio codecsAudioCoding.com
– home of FAAC and FAAD2
Official MPEG web site
* AAC improvements and extensions (2004) * - RTP Payload Format for MPEG-4 Audio/Visual Streams * - RTP Payload Format for Transport of MPEG-4 Elementary Streams * - The Codecs Parameter for "Bucket" Media Types * - MIME Type Registration for MPEG-4 {{navboxes , list1= {{Compression formats {{MPEG {{High-definition {{Audio broadcasting {{Authority control Audio codecs Lossy compression algorithms MPEG Open standards covered by patents