Advanced Audio Coding

Advanced Audio Coding

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Advanced Audio Coding is a standardized, lossy
Lossy data compression
In information technology, "lossy" compression is a data encoding method that compresses data by discarding some of it. The procedure aims to minimize the amount of data that need to be held, handled, and/or transmitted by a computer...

 compression and encoding
Encoder
An encoder is a device, circuit, transducer, software program, algorithm or person that converts information from one format or code to another, for the purposes of standardization, speed, secrecy, security, or saving space by shrinking size.-Media:...

 scheme for digital audio
Digital audio
Digital audio is sound reproduction using pulse-code modulation and digital signals. Digital audio systems include analog-to-digital conversion , digital-to-analog conversion , digital storage, processing and transmission components...

. Designed to be the successor of the MP3
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...

 format, AAC generally achieves better sound quality than MP3 at similar bit rate
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

s.

AAC has been standardized by ISO and IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

, as part of the MPEG-2
MPEG-2
MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission...

 and MPEG-4
MPEG-4
MPEG-4 is a method of defining compression of audio and visual digital data. It was introduced in late 1998 and designated a standard for a group of audio and video coding formats and related technology agreed upon by the ISO/IEC Moving Picture Experts Group under the formal standard ISO/IEC...

 specifications. Part of the AAC known as High-Efficiency Advanced Audio Coding (HE-AAC) which is part of MPEG-4 Audio is also adopted into digital radio
Digital radio
Digital radio has several meanings:1. Today the most common meaning is digital radio broadcasting technologies, such as the digital audio broadcasting system, also known as Eureka 147. In these systems, the analog audio signal is digitized into zeros and ones, compressed using formats such as...

 standards like DAB+ and Digital Radio Mondiale
Digital Radio Mondiale
Digital Radio Mondiale is a set of digital audio broadcasting technologies designed to work over the bands currently used for AM broadcasting, particularly shortwave...

, as well as mobile television standards DVB-H
DVB-H
DVB-H is one of three prevalent mobile TV formats. It is a technical specification for bringing broadcast services to mobile handsets. DVB-H was formally adopted as ETSI standard EN 302 304 in November 2004. The DVB-H specification can be downloaded from the official DVB-H website...

 and ATSC-M/H
ATSC-M/H
ATSC-M/H is a standard in the USA for mobile digital TV, that allows TV broadcasts to be received by mobile devices.....

.

AAC supports inclusion of 48 full-bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...

 (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
STEREO
STEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...

 is satisfactory to modest requirements at 96 kbit/s in joint stereo mode; however, hi-fi transparency
Transparency (data compression)
In data compression or psychoacoustics, transparency is the ideal result of lossy data compression. If a lossy compressed result is perceptually indistinguishable from the uncompressed input, then the compression can be declared to be transparent...

 demands data rates of at least 128 kbit/s (VBR
Variable bitrate
Variable bitrate is a term used in telecommunications and computing that relates to the bitrate used in sound or video encoding. As opposed to constant bitrate , VBR files vary the amount of output data per time segment...

). The MPEG-2 audio tests showed that AAC meets the requirements referred to as "transparent" for the ITU
Itu
Itu is an old and historic municipality in the state of São Paulo in Brazil. The population in 2009 was 157,384 and the area is 641.68 km². The elevation is 583 m. This place name comes from the Tupi language, meaning big waterfall. Itu is linked with the highway numbered the SP-75 and are flowed...

 at 128 kbit/s for stereo, and 320 kbit/s for 5.1 audio.

AAC is also the default or standard audio format for iPhone
IPhone
The iPhone is a line of Internet and multimedia-enabled smartphones marketed by Apple Inc. The first iPhone was unveiled by Steve Jobs, then CEO of Apple, on January 9, 2007, and released on June 29, 2007...

, iPod
IPod
iPod is a line of portable media players created and marketed by Apple Inc. The product line-up currently consists of the hard drive-based iPod Classic, the touchscreen iPod Touch, the compact iPod Nano, and the ultra-compact iPod Shuffle...

, iPad
IPad
The iPad is a line of tablet computers designed, developed and marketed by Apple Inc., primarily as a platform for audio-visual media including books, periodicals, movies, music, games, and web content. The iPad was introduced on January 27, 2010 by Apple's then-CEO Steve Jobs. Its size and...

, Nintendo DSi
Nintendo DSi
The is a handheld game system created by Nintendo and launched in 2008 and 2009 in Japan, North America, PAL territories, and other regions. It is the third iteration of the Nintendo DS, and its primary market rival is Sony's PlayStation Portable...

, iTunes
ITunes
iTunes is a media player computer program, used for playing, downloading, and organizing digital music and video files on desktop computers. It can also manage contents on iPod, iPhone, iPod Touch and iPad....

, DivX Plus Web Player and PlayStation 3
PlayStation 3
The is the third home video game console produced by Sony Computer Entertainment and the successor to the PlayStation 2 as part of the PlayStation series. The PlayStation 3 competes with Microsoft's Xbox 360 and Nintendo's Wii as part of the seventh generation of video game consoles...

. It is supported on PlayStation Portable
PlayStation Portable
The is a handheld game console manufactured and marketed by Sony Corporation Development of the console was announced during E3 2003, and it was unveiled on , 2004, at a Sony press conference before E3 2004...

, Wii
Wii
The Wii is a home video game console released by Nintendo on November 19, 2006. As a seventh-generation console, the Wii primarily competes with Microsoft's Xbox 360 and Sony's PlayStation 3. Nintendo states that its console targets a broader demographic than that of the two others...

 (with the Photo Channel 1.1 update installed), Sony Walkman MP3 series and later, mobile phones made by Sony Ericsson
Sony Ericsson
Sony Ericsson Mobile Communications AB is a joint venture established on October 1, 2001 by the Japanese consumer electronics company Sony Corporation and the Swedish telecommunications company Ericsson to manufacture mobile phones....

; Nokia
Nokia
Nokia Corporation is a Finnish multinational communications corporation that is headquartered in Keilaniemi, Espoo, a city neighbouring Finland's capital Helsinki...

; Android; and webOS-based mobile phones. AAC has also seen moderate adoption on in-dash car audio especially on high-end units such as the Pioneer AVIC
Pioneer Corporation
is a multinational corporation that specializes in digital entertainment products, based in Kawasaki, Kanagawa, Japan. The company was founded in 1938 in Tokyo as a radio and speaker repair shop...

 series.

History


AAC was developed with the cooperation and contributions of companies including AT&T Bell Laboratories, Fraunhofer IIS
Fraunhofer Society
The Fraunhofer Society is a German research organization with 60 institutes spread throughout Germany, each focusing on different fields of applied science . It employs around 18,000, mainly scientists and engineers, with an annual research budget of about €1.65 billion...

, Dolby Laboratories
Dolby Laboratories
Dolby Laboratories, Inc. , often shortened to Dolby Labs, is an American company specializing in audio noise reduction and audio encoding/compression.-History:...

, Sony Corporation and Nokia
Nokia
Nokia Corporation is a Finnish multinational communications corporation that is headquartered in Keilaniemi, Espoo, a city neighbouring Finland's capital Helsinki...

. It was officially declared an international standard by the Moving Picture Experts Group
Moving Picture Experts Group
The Moving Picture Experts Group is a working group of experts that was formed by ISO and IEC to set standards for audio and video compression and transmission. It was established in 1988 by the initiative of Hiroshi Yasuda and Leonardo Chiariglione, who has been from the beginning the Chairman...

 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
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

/IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

 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
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 1.5 Mbit/s without excessive quality loss, making video CDs, digital cable/satellite TV and digital audio broadcasting possible.Today, MPEG-1 has become...

 audio formats (MP1, MP2
MPEG-1 Audio Layer II
MPEG-1 Audio Layer II or MPEG-2 Audio Layer II is a lossy audio compression format defined by ISO/IEC 11172-3 alongside MPEG-1 Audio Layer I and MPEG-1 Audio Layer III...

 and MP3
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...

).

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
Noise shaping
Noise shaping is a technique typically used in digital audio, image, and video processing, usually in combination with dithering, as part of the process of quantization or bit-depth reduction of a digital signal...

 (TNS), the Dolby Kaiser Window (described below), a nonuniform quantizer
Quantization (signal processing)
Quantization, in mathematics and digital signal processing, is the process of mapping a large set of input values to a smaller set – such as rounding values to some unit of precision. A device or algorithmic function that performs quantization is called a quantizer. The error introduced by...

, 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 standard and became known as MPEG-4 Part 3
MPEG-4 Part 3
MPEG-4 Part 3 or MPEG-4 Audio is the third part of the ISO/IEC MPEG-4 international standard developed by Moving Picture Experts Group. It specifies audio coding methods...

, 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
TwinVQ
TwinVQ is an audio compression technique developed by Nippon Telegraph and Telephone Corporation Human Interface Laboratories in 1994...

, CELP, HVXC, Text-To-Speech Interface and MPEG-4 Structured Audio
MPEG-4 Structured Audio
MPEG-4 Structured Audio is an ISO/IEC standard for describing sound. It was published as subpart 5 of MPEG-4 Part 3 in 1999....

. Another notable addition in this version of the AAC standard is Perceptual Noise Substitution (PNS). In that regard, the ACC 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 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
AAC-LD
The MPEG-4 Low Delay Audio Coder is audio compression format 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 format...

) 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
HE-AAC
High-Efficiency Advanced Audio Coding is a lossy data compression scheme for digital audio defined as a MPEG-4 Audio profile in ISO/IEC 14496-3. It is an extension of Low Complexity AAC optimized for low-bitrate applications such as streaming audio...

 Profile (AAC LC with SBR
Spectral band replication
Spectral band replication is a technology to enhance audio or speech codecs, especially at low bit rates and is based on harmonic redundancy in the frequency domain....

) 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
European Telecommunications Standards Institute
The European Telecommunications Standards Institute is an independent, non-profit, standardization organization in the telecommunications industry in Europe, with worldwide projection...

) as TS 102005.

The MPEG-4 Part 3
MPEG-4 Part 3
MPEG-4 Part 3 or MPEG-4 Audio is the third part of the ISO/IEC MPEG-4 international standard developed by Moving Picture Experts Group. It specifies audio coding methods...

 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
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...

, known as MP3 format, which was specified by ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

/IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

 in 11172-3 (MPEG-1
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 1.5 Mbit/s without excessive quality loss, making video CDs, digital cable/satellite TV and digital audio broadcasting possible.Today, MPEG-1 has become...

 Audio) and 13818-3 (MPEG-2
MPEG-2
MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission...

 Audio).

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

Improvements include:
  • More sample frequencies (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-rate
    Bit rate
    In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

    s and variable frame length. Standardized constant bit rate with bit reservoir.
  • Higher efficiency and simpler filterbank (rather than MP3's hybrid coding, AAC uses a pure MDCT
    Modified discrete cosine transform
    The modified discrete cosine transform is a Fourier-related transform based on the type-IV discrete cosine transform , with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset,...

    )
  • Higher coding efficiency for stationary signals
    Stationary process
    In the mathematical sciences, a stationary process is a stochastic process whose joint probability distribution does not change when shifted in time or space...

     (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)
  • Can use Kaiser-Bessel derived window function to eliminate spectral leakage
    Spectral leakage
    Spectral leakage is an effect in the frequency analysis of finite-length signals or finite-length segments of infinite signals where it appears as if some energy has "leaked" out of the original signal spectrum into other frequencies....

     at the expense of widening the main lobe
    Main lobe
    The main lobe, or main beam, of an antenna radiation pattern is the lobe containing the maximum power. This is the lobe that exhibits the greatest field strength....

  • Much better handling of audio frequencies above 16 kHz
  • More flexible joint stereo
    Joint (audio engineering)
    In audio engineering, joint refers to a joining of several channels of similar information in order to obtain higher quality, a smaller file size, or both.-Joint stereo:...

     (different methods can be used in different frequency ranges)
  • Adds additional modules (tools) to increase compression efficiency: TNS
    Noise shaping
    Noise shaping is a technique typically used in digital audio, image, and video processing, usually in combination with dithering, as part of the process of quantization or bit-depth reduction of a digital signal...

    , Backwards Prediction, 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. 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 better 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.

Also, in terms of comparison, due to its popularity, MP3 format was much more explored than AAC, and there are fewer available AAC codecs than MP3 ones.

How AAC works


AAC is a wideband
Wideband
In communications, wideband is a relative term used to describe a wide range of frequencies in a spectrum. A system is typically described as wideband if the message bandwidth significantly exceeds the channel's coherence bandwidth....

 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 signal is converted from time-domain to frequency-domain using forward modified discrete cosine transform (MDCT)
    Modified discrete cosine transform
    The modified discrete cosine transform is a Fourier-related transform based on the type-IV discrete cosine transform , with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset,...

    . 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
    Psychoacoustics is the scientific study of sound perception. More specifically, it is the branch of science studying the psychological and physiological responses associated with sound...

     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
    Luhn mod N algorithm
    The Luhn mod N algorithm is an extension to the Luhn algorithm that allows it to work with sequences of non-numeric characters...

     is applied to each frame


The MPEG-4
MPEG-4
MPEG-4 is a method of defining compression of audio and visual digital data. It was introduced in late 1998 and designated a standard for a group of audio and video coding formats and related technology agreed upon by the ISO/IEC Moving Picture Experts Group under the formal standard ISO/IEC...

 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.
  • The MPEG-4
    MPEG-4
    MPEG-4 is a method of defining compression of audio and visual digital data. It was introduced in late 1998 and designated a standard for a group of audio and video coding formats and related technology agreed upon by the ISO/IEC Moving Picture Experts Group under the formal standard ISO/IEC...

     audio coding algorithm family spans the range from low bitrate 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
    Modified discrete cosine transform
    The modified discrete cosine transform is a Fourier-related transform based on the type-IV discrete cosine transform , with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset,...

    ) 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) (MPEG-4 AAC-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
  • 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


(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.)

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.

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 tool kit'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 MPEG-4 Low Delay Audio Coder (AAC-LD
AAC-LD
The MPEG-4 Low Delay Audio Coder is audio compression format 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 format...

) 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. 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. For this reason FOSS
Foss
Foss may refer toPeople*Foss , people with the last name Foss*Foss Shanahan , New Zealand diplomat*Foss Westcott , English bishop...

 implementations such as FFmpeg
FFmpeg
FFmpeg is a free software project that produces libraries and programs for handling multimedia data. The most notable parts of FFmpeg are libavcodec, an audio/video codec library used by several other projects, libavformat, an audio/video container mux and demux library, and the ffmpeg command line...

 and FAAC
FAAC
FAAC or Freeware Advanced Audio Coder is a software project which includes the AAC encoder FAAC and decoder FAAD2. It supports MPEG-2 AAC as well as MPEG-4 AAC. It supports several MPEG-4 Audio object types , file formats , multichannel and gapless encoding/decoding and MP4 metadata tags...

 may be distributed in source
Source code
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing 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):
  • Perceptual Noise Substitution (PNS), added in MPEG-4
    MPEG-4 Part 3
    MPEG-4 Part 3 or MPEG-4 Audio is the third part of the ISO/IEC MPEG-4 international standard developed by Moving Picture Experts Group. It specifies audio coding methods...

     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
    AAC-LD
    The MPEG-4 Low Delay Audio Coder is audio compression format 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 format...

     (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)
    Spectral band replication
    Spectral band replication is a technology to enhance audio or speech codecs, especially at low bit rates and is based on harmonic redundancy in the frequency domain....

     and AAC LC; used for low bitrates; defined in 2003;
  • HE-AAC v2, a.k.a. aacPlus v2 or eAAC+, the combination of Parametric Stereo (PS)
    Parametric Stereo
    Parametric Stereo is a feature and an Audio Object Type defined and used in MPEG-4 Part 3 to further enhance efficiency in low bandwidth stereo media. Advanced Audio Coding Low Complexity combined with Spectral band replication and Parametric Stereo was defined as HE-AAC v2...

     and HE-AAC; used for even lower bitrates; defined in 2004 and 2006;
  • MPEG-4 Scalable To Lossless (SLS)
    MPEG-4 SLS
    MPEG-4 SLS, or MPEG-4 Scalable to Lossless as per ISO/IEC 14496-3:2005/Amd 3:2006 , is an extension to the MPEG-4 Part 3 standard to allow lossless audio compression scalable to lossy MPEG-4 General Audio coding methods...

    , defined in 2006, 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
3GP
3GP is a multimedia container format defined by the Third Generation Partnership Project for 3G UMTS multimedia services. It is used on 3G mobile phones but can also be played on some 2G and 4G phones....

 and other ISO base media file format
ISO base media file format
ISO base media file format defines a general structure for time-based multimedia files such as video and audio. It is used as the basis for other media file formats...

-based container formats for storage, AAC audio data may be packaged in a more basic format called Audio Data Interchange Format (ADIF), consisting of a single header followed by the raw AAC audio data blocks. 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. 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. These containers, as well as a raw AAC stream, may bear the .aac file extension. Two more formats are defined in MPEG-4 Part 3
MPEG-4 Part 3
MPEG-4 Part 3 or MPEG-4 Audio is the third part of the ISO/IEC MPEG-4 international standard developed by Moving Picture Experts Group. It specifies audio coding methods...

: 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.

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-Tb
ISDB-Tb is the short for International System for Digital Broadcast, Terrestrial, Brazilian version.It is a Digital TV system based on Japanese ISDB-T . ISDB-Tb system is also known as SBTVD and is used in Brazil...

 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
H.264/MPEG-4 AVC
H.264/MPEG-4 Part 10 or AVC is a standard for video compression, and is currently one of the most commonly used formats for the recording, compression, and distribution of high definition video...

 compression for video normally use HE-AAC for audio.

iTunes and iPod


In April 2003, Apple brought mainstream attention to AAC by announcing that its iTunes
ITunes
iTunes is a media player computer program, used for playing, downloading, and organizing digital music and video files on desktop computers. It can also manage contents on iPod, iPhone, iPod Touch and iPad....

 and iPod
IPod
iPod is a line of portable media players created and marketed by Apple Inc. The product line-up currently consists of the hard drive-based iPod Classic, the touchscreen iPod Touch, the compact iPod Nano, and the ultra-compact iPod Shuffle...

 products would support songs in MPEG-4 AAC format (via a firmware
Firmware
In electronic systems and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices...

 update for older iPods). Customers could download music in a closed-source Digital Rights Management (DRM)
Digital rights management
Digital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...

-restricted form of AAC (see FairPlay
FairPlay
FairPlay is a digital rights management technology created by Apple Inc., based on technology created by the company Veridisc. FairPlay is built into the QuickTime multimedia software and used by the iPhone, iPod, iPad, Apple TV, iTunes, and iTunes Store and the App Store. Formerly, all songs in...

) via the iTunes Store
ITunes Store
The iTunes Store is a software-based online digital media store operated by Apple. Opening as the iTunes Music Store on April 28, 2003, with over 200,000 items to purchase, it is, as of April 2008, the number-one music vendor in the United States...

 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
Peer-to-peer
Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...

 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.

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
HE-AAC
High-Efficiency Advanced Audio Coding is a lossy data compression scheme for digital audio defined as a MPEG-4 Audio profile in ISO/IEC 14496-3. It is an extension of Low Complexity AAC optimized for low-bitrate applications such as streaming audio...

 (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

  • Archos
    Archos
    Archos is a French consumer electronics company that was established in 1988 by Henri Crohas. Archos manufactures portable media players and portable data storage devices. The name is an anagram of Crohas' last name, and it is also Greek for 'master'...

  • Creative Zen
    Creative Zen
    The Creative ZEN is a range of digital audio players and portable media players made by Creative Technology. The players evolved from the now-defunct NOMAD brand through the NOMAD Jukebox series...

     Portable
  • Microsoft
    Microsoft
    Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

     Zune
    Zune
    Zune is a digital media brand owned by Microsoft which includes a line of portable media players, a digital media player software for Windows machines, a music subscription service known as a 'Zune Music Pass', music and video streaming for the Xbox 360 via the Zune Software, music, TV and movie...

  • SanDisk
    SanDisk
    SanDisk Corporation is an American multinational corporation that designs, develops and manufactures data storage solutions in a range of form factors using the flash memory, controller and firmware technologies. It was founded in 1988 by Dr. Eli Harari and Sanjay Mehrotra, non-volatile memory...

     Sansa
    SanDisk Sansa
    The SanDisk Sansa is a line of 2 to 16 gigabyte flash memory-based digital audio players and portable media players produced by SanDisk.- Sansa Fuze+:...

     (some models)
  • Sony
    Sony
    , commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....

     PlayStation Portable
    PlayStation Portable
    The is a handheld game console manufactured and marketed by Sony Corporation Development of the console was announced during E3 2003, and it was unveiled on , 2004, at a Sony press conference before E3 2004...

     (PSP) with firmware 2.0 or greater
  • Sony Walkman
    Walkman
    Walkman is a Sony brand tradename originally used for portable audio cassette, and now used to market Sony's portable audio and video players as well as a line of Sony Ericsson mobile phones...

  • Nintendo DSi
    Nintendo DSi
    The is a handheld game system created by Nintendo and launched in 2008 and 2009 in Japan, North America, PAL territories, and other regions. It is the third iteration of the Nintendo DS, and its primary market rival is Sony's PlayStation Portable...

  • Nintendo 3DS
    Nintendo 3DS
    The is a portable game console produced by Nintendo. The autostereoscopic device is able to project stereoscopic 3D effects without the use of 3D glasses or any additional accessories. The Nintendo 3DS features backward compatibility with Nintendo DS series software, including Nintendo DSi software...

  • Any portable player that fully supports the Rockbox
    Rockbox
    Rockbox is a replacement for the standard firmware in various forms of digital audio players . It offers an alternative to the player's operating system, in many cases without removing the original firmware, which provides a plug-in architecture for adding various enhancements and functions...

     third party firmware

Mobile phones


For a number of years, many mobile phones from manufacturers such as Nokia
Nokia
Nokia Corporation is a Finnish multinational communications corporation that is headquartered in Keilaniemi, Espoo, a city neighbouring Finland's capital Helsinki...

, Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...

, Samsung
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...

, Sony Ericsson
Sony Ericsson
Sony Ericsson Mobile Communications AB is a joint venture established on October 1, 2001 by the Japanese consumer electronics company Sony Corporation and the Swedish telecommunications company Ericsson to manufacture mobile phones....

, BenQ-Siemens
BenQ-Siemens
BenQ-Siemens was the mobile communications subsidiary of Taiwanese BenQ Corp. The division was formed out of BenQ's acquisition of the then struggling Siemens mobile group in 2005. The stated goal of the company was to pull together BenQ's lifestyle experience, their design team and Siemens'...

 and Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....

 have supported AAC playback. The first such phone was the Nokia 5510
Nokia 5510
The Nokia 5510 is a type of 2G mobile phone released in 2001. Aside from its music playing abilities , many aspects of the phone are similar or identical to its predecessor, the Nokia 3310/3330. It has a 64 MB memory for storing audio files....

 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 Ericsson
    Sony Ericsson Mobile Communications AB is a joint venture established on October 1, 2001 by the Japanese consumer electronics company Sony Corporation and the Swedish telecommunications company Ericsson to manufacture mobile phones....

     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
    Sony Ericsson P990
    Sony Ericsson P990 is a smartphone and the successor of Sony Ericsson P910. The phone uses the UIQ 3 software platform, which is based upon Symbian OS 9.1. It was released in August 2006. The P990 has a numeric keypad that flips open to reveal a full QWERTY keyboard below the display, on the phone...

    , K610
    Sony Ericsson K610
    The Sony Ericsson K610i is a 3G phone that Sony Ericsson announced at the 3GSM World Congress on February 13, 2006. It was promoted as the smallest and lightest 3G phone available. It has been succeeded by the K530.- Features :...

    , 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
  • BlackBerry
    BlackBerry
    BlackBerry is a line of mobile email and smartphone devices developed and designed by Canadian company Research In Motion since 1999.BlackBerry devices are smartphones, designed to function as personal digital assistants, portable media players, internet browsers, gaming devices, and much more...

    : RIM's latest series of Smartphones such as the 8100 ("Pearl"), 9500 ("Storm") and 8800 support AAC.
  • Apple's iPhone
    IPhone
    The iPhone is a line of Internet and multimedia-enabled smartphones marketed by Apple Inc. The first iPhone was unveiled by Steve Jobs, then CEO of Apple, on January 9, 2007, and released on June 29, 2007...

     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.
  • All recent Android phones support AAC-LC, HE-AAC and HE-AAC v2 in MP4 or M4A containers along with several other audio formats. From Android 3.1 also raw ADTS files are supported. Android 4.0 can also encode these kind of files.
  • The HTC Dream
    HTC Dream
    The HTC Dream is an Internet-enabled smartphone with an operating system designed by Google and hardware designed by HTC...

     (Also known as the T-Mobile G1) is described as supporting certain subset of the full AAC format. As of 2009-04-13 at least several forms of AAC files played while others did not play.
  • WebOS by HP/Palm supports AAC, AAC+, eAAC+, and .m4a containers in its native music player as well as several third-party players. However, it does not support Apple's FairPlay DRM files downloaded from iTunes.
  • Windows Phone 7
    Windows Phone 7
    Windows Phone is a mobile operating system developed by Microsoft, and is the successor to its Windows Mobile platform, although incompatible with it. Unlike its predecessor, it is primarily aimed at the consumer market rather than the enterprise market...

    : WP7's Silverlight runtime supports AAC-LC, HE-AAC and HE-AAC v2 decoding.

Other devices

  • Apple's iPad
    IPad
    The iPad is a line of tablet computers designed, developed and marketed by Apple Inc., primarily as a platform for audio-visual media including books, periodicals, movies, music, games, and web content. The iPad was introduced on January 27, 2010 by Apple's then-CEO Steve Jobs. Its size and...

    : Supports AAC and FairPlay protected AAC files used as the default encoding format in the iTunes store.
  • Palm OS
    Palm OS
    Palm OS is a mobile operating system initially developed by Palm, Inc., for personal digital assistants in 1996. Palm OS is designed for ease of use with a touchscreen-based graphical user interface. It is provided with a suite of basic applications for personal information management...

     PDAs
    Personal digital assistant
    A personal digital assistant , also known as a palmtop computer, or personal data assistant, is a mobile device that functions as a personal information manager. Current PDAs often have the ability to connect to the Internet...

    : Many Palm OS based PDAs and smartphones can play AAC and HE-AAC with the 3rd party software Pocket Tunes
    Pocket Tunes
    Pocket Tunes by Normsoft, Inc. is shareware software used for playing music, Internet radio, podcasts, and other audio files for Palm OS 5 and Windows Mobile 5 or 6. Pocket Tunes supports MP3, AAC, HE-AAC, WMA, and Windows Media DRM files. It also supports MTP for transferring audio files from...

    . 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 PalmOS programs supporting AAC include Kinoma Player and AeroPlayer.
  • Microsoft Windows Mobile platforms support AAC either by the native Windows Media Player
    Windows Media Player
    Windows Media Player is a media player and media library application developed by Microsoft that is used for playing audio, video and viewing images on personal computers running the Microsoft Windows operating system, as well as on Pocket PC and Windows Mobile-based devices...

     or by third-party products (TCPMP, CorePlayer)
  • Epson supports AAC playback in the P-2000 and P-4000 Multimedia/Photo Storage Viewers. This support is not available with their older models, however.
  • The Sony Reader
    Sony Reader
    The Sony Reader is a line of e-book readers manufactured by Sony. It uses an electronic paper display developed by E Ink Corporation, is viewable in direct sunlight, requires no power to maintain a static image, and is usable in portrait or landscape orientation.Sony sells e-books for the Reader...

     portable eBook 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.
  • Nearly every major car stereo manufacturer offers models that will play back .m4a files recorded onto CD in a data format. This includes Pioneer
    Pioneer Corporation
    is a multinational corporation that specializes in digital entertainment products, based in Kawasaki, Kanagawa, Japan. The company was founded in 1938 in Tokyo as a radio and speaker repair shop...

    , Sony
    Sony
    , commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....

    , Alpine
    Alpine Electronics
    is traditionally known as an aftermarket car audio and navigation systems manufacturer, famed for their high quality, premium in-car audio units commonly known as headunits. It is a subsidiary of Alps Electric Co. and its registered head office is in Tokyo, Japan. However its main offices, or the...

    , Kenwood, Clarion
    Clarion (car audio)
    is a Japanese manufacturer of car audio, automotive navigation systems, AutoPCs, visual equipment, bus equipment, and communication equipment.Up until the end of 2005, products in Japan were marketed under the brand name AddZest, while outside of Japan the same product typically carried the Clarion...

    , Panasonic
    Panasonic
    Panasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...

    , and JVC
    JVC
    , usually referred to as JVC, is a Japanese international consumer and professional electronics corporation based in Yokohama, Japan which was founded in 1927...

    .
  • The Sonos
    Sonos
    Sonos is a consumer electronics company based in Santa Barbara, California. It was founded in 2002 by John MacFarlane, who previously founded Software.com. The company’s main product is the Sonos Multi-Room Music System.-History:...

     Digital Media Player supports playback of AAC files.
  • The Barnes & Noble Nook Color
    Nook Color
    The Nook Color is a color version of the Nook e-reader device by Barnes & Noble. It is a 7-inch tablet with full-color multitouch touchscreen input. The device is designed for full-color viewing of books, newspapers, magazines, and children's picture books...

     electronic-book reader supports playback of AAC encoded files.
  • The Roku SoundBridge
    SoundBridge
    SoundBridge is a remote hardware device from Roku designed to play internet radio or digital audio streamed to it across a home network, either WiFi or Ethernet. SoundBridge devices directly browse the Radio Roku Internet Radio Guide....

     network audio player supports playback of AAC encoded files.
  • The Squeezebox network audio player (made by Slim Devices
    Slim Devices
    Slim Devices, Inc. is a consumer electronics company based in Mountain View, California, United States. Their main product is the Squeezebox network music player which connects to a home ethernet or Wi-Fi network, and allows the owner to stream digital audio over the network to a stereo...

    , a Logitech
    Logitech
    Logitech International S.A. is a global provider of personal peripherals for computers and other digital platforms headquartered in Romanel-sur-Morges, Switzerland. The company develops and markets products like peripheral devices for PCs, including keyboards, mice, microphones, game controllers...

     company) supports playback of AAC files.
  • The PlayStation 3
    PlayStation 3
    The is the third home video game console produced by Sony Computer Entertainment and the successor to the PlayStation 2 as part of the PlayStation series. The PlayStation 3 competes with Microsoft's Xbox 360 and Nintendo's Wii as part of the seventh generation of video game consoles...

    supports encoding and decoding of AAC files.
  • The Xbox 360
    Xbox 360
    The Xbox 360 is the second video game console produced by Microsoft and the successor to the Xbox. The Xbox 360 competes with Sony's PlayStation 3 and Nintendo's Wii as part of the seventh generation of video game consoles...

    supports streaming of AAC through the Zune software, and off supported iPods connected through the USB port
  • The Wii
    Wii
    The Wii is a home video game console released by Nintendo on November 19, 2006. As a seventh-generation console, the Wii primarily competes with Microsoft's Xbox 360 and Sony's PlayStation 3. Nintendo states that its console targets a broader demographic than that of the two others...

     video game console 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.
  • The Livescribe
    Livescribe
    The Livescribe paper-based computing platform 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 digital audio recorder...

     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.

Flash Player


A very common program supporting AAC playback is Flash Player
Adobe Flash Player
The Adobe Flash Player is software for viewing multimedia, Rich Internet Applications and streaming video and audio, on a computer web browser or on supported mobile devices. Flash Player runs SWF files that can be created by the Adobe Flash authoring tool, by Adobe Flex or by a number of other...

, version 9, update 3 and above. Since Flash Player is also a browser plugin, it can play AAC files through a browser as well.

The Rockbox
Rockbox
Rockbox is a replacement for the standard firmware in various forms of digital audio players . It offers an alternative to the player's operating system, in many cases without removing the original firmware, which provides a plug-in architecture for adding various enhancements and functions...

 open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...

 firmware
Firmware
In electronic systems and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices...

 (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
Xbox 360
The Xbox 360 is the second video game console produced by Microsoft and the successor to the Xbox. The Xbox 360 competes with Sony's PlayStation 3 and Nintendo's Wii as part of the seventh generation of video game consoles...

 is available as a free download from Xbox Live
Xbox Live
Xbox Live is an online multiplayer gaming and digital media delivery service created and operated by Microsoft Corporation. It is currently the only online gaming service on consoles that charges users a fee to play multiplayer gaming. It was first made available to the Xbox system in 2002...

.

Other software media players


Almost all current computer media players include built-in decoders for AAC, or can utilize a library
Library (computer science)
In computer science, a library is a collection of resources used to develop software. These may include pre-written code and subroutines, classes, values or type specifications....

 to decode it. On Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

, DirectShow
DirectShow
DirectShow , codename Quartz, is a multimedia framework and API produced by Microsoft for software developers to perform various operations with media files or streams. It is the replacement for Microsoft's earlier Video for Windows technology...

 can be used this way with the corresponding filters to enable AAC playback in any DirectShow
DirectShow
DirectShow , codename Quartz, is a multimedia framework and API produced by Microsoft for software developers to perform various operations with media files or streams. It is the replacement for Microsoft's earlier Video for Windows technology...

 based player. Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 supports AAC via the QuickTime
QuickTime
QuickTime is an extensible proprietary multimedia framework developed by Apple Inc., capable of handling various formats of digital video, picture, sound, panoramic images, and interactivity. The classic version of QuickTime is available for Windows XP and later, as well as Mac OS X Leopard and...

 libraries.

Software player applications of particular note include:
  • 3ivx MPEG-4
    3ivx
    3ivx is a video codec suite, created by 3ivx Technologies, based in Sydney, Australia, that allows the creation of MPEG-4 compliant data streams. It has been designed around a need for decreased processing power for use mainly in embedded systems. First versions were published in 2001...

     - A suite of DirectShow and QuickTime plugins which support AAC encoding and/or AAC/ HE-AAC decoding in any DirectShow application
  • CorePlayer also supports LC and HE AAC.
  • Easy CD-DA Extractor for Windows
    Microsoft Windows
    Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

    , CD Ripper and audio converter, which includes an AAC encoder that supports LC and HE AAC.
  • ffdshow
    Ffdshow
    ffdshow is a media decoder and encoder mainly used for the fast and high-quality decoding of video in the MPEG-4 ASP and AVC formats, but it supports numerous other video and audio formats as well...

     is a free open source
    Open source
    The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...

     DirectShow
    DirectShow
    DirectShow , codename Quartz, is a multimedia framework and API produced by Microsoft for software developers to perform various operations with media files or streams. It is the replacement for Microsoft's earlier Video for Windows technology...

     filter for Microsoft Windows
    Microsoft Windows
    Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

     operating systems that uses FAAD2 to support AAC decoding.
  • foobar2000
    Foobar2000
    foobar2000 is a freeware audio player for Windows developed by Peter Pawlowski, a former freelance contractor for Nullsoft. It is known for its highly modular design and extensive SDK which allows third-party developers to do such things as completely replace the interface...

     is a freeware
    Freeware
    Freeware is computer software that is available for use at no cost or for an optional fee, but usually with one or more restricted usage rights. Freeware is in contrast to commercial software, which is typically sold for profit, but might be distributed for a business or commercial purpose in the...

     audio player
    Audio player (software)
    An audio player is a kind of media player for playing back digital audio, including optical discs such as CDs, SACDs, DVD-Audio, HDCD, audio files and streaming audio....

     for Windows
    Microsoft Windows
    Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

     that supports LC and HE AAC.
  • JAAD is an open-source decoder written in Java
    Java
    Java is an island of Indonesia. With a population of 135 million , it is the world's most populous island, and one of the most densely populated regions in the world. It is home to 60% of Indonesia's population. The Indonesian capital city, Jakarta, is in west Java...

    .
  • K-Multimedia Player
    K-Multimedia Player
    K-Multimedia Player is a media player software for Microsoft Windows which can play a large number of formats including VCD, DVD, AVI, MKV, Ogg, OGM, 3GP, MPEG-1/2/4, WMV, RealMedia, FLV and QuickTime...

     also supports AAC.
  • KSP Sound Player also supports AAC.
  • MediaMonkey
    MediaMonkey
    MediaMonkey is a proprietary digital media player and media library application developed by Ventis Media Inc., for organizing and playing audio on Microsoft Windows operating systems. By using plugins, it can be extended to handle video and other media formats as well.MediaMonkey is available in a...

  • Media Player Classic Home Cinema
  • MPlayer
    MPlayer
    MPlayer is a free and open source media player. The program is available for all major operating systems, including Linux and other Unix-like systems, Microsoft Windows and Mac OS X. Versions for OS/2, Syllable, AmigaOS and MorphOS are also available. The Windows version works, with some minor...

     or xine
    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 that supports different frontend player applications. Another important feature of xine is the ability to manually correct the synchronization...

     are often used as AAC decoders on Linux
    Linux
    Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

     or Macintosh
    Macintosh
    The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...

    .
  • RealPlayer
    RealPlayer
    RealPlayer is a cross-platform media player by RealNetworks that plays a number of multimedia formats including MP3, MPEG-4, QuickTime, Windows Media, and multiple versions of proprietary RealAudio and RealVideo formats.-History:...

     includes RealNetworks
    RealNetworks
    RealNetworks, Inc. is a provider of Internet media delivery software and services based in Downtown Seattle, Washington, United States. The company is the creator of RealAudio, a compressed audio format; RealVideo, a compressed video format; RealPlayer, a media player; RealDownloader, a download...

    ' RealAudio 10 AAC encoder.
  • Songbird
    Songbird (software)
    Songbird is a free and open source software audio player and web browser, with a stated mission "to incubate Songbird, the first Web player, to catalyze and champion a diverse, open Media Web."...

     for Windows
    Microsoft Windows
    Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

    , Linux
    Linux
    Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

     and Mac OS X
    Mac OS X
    Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

     supports AAC, including the DRM rights management encoding used for purchased music from the iTunes Store, with a plug-in.
  • Sony SonicStage
    SonicStage
    SonicStage is the name for Sony software that is used for managing portable devices when they are plugged into a computer running Microsoft Windows. It comprises a music player and library manager, similar to iTunes, Windows Media Player and RealPlayer. It is used to manage the library of ATRAC...

     also support AAC.
  • VLC media player
    VLC media player
    VLC media player is a free and open source media player and multimedia framework written by the VideoLAN project.VLC is a portable multimedia player, encoder, and streamer supporting many audio and video codecs and file formats as well as DVDs, VCDs, and various streaming protocols. It is able to...

     supports playback and encoding of MP4 and AAC files.
  • Winamp
    Winamp
    Winamp is a media player for Windows-based PCs and Android devices, written by Nullsoft, now a subsidiary of AOL. It is proprietary freeware/shareware, multi-format, extensible with plug-ins and skins, and is noted for its graphical sound visualization, playlist, and media library features.Winamp...

     for Windows
    Microsoft Windows
    Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

    , which includes an AAC encoder that supports LC and HE AAC;
  • Windows Media Player 12, released with Windows 7, supports playback of AAC files natively.
  • Another Real product, Rhapsody
    Rhapsody (online music service)
    Rhapsody is an online music store subscription service, launched in December 2001, and available in the United States only. On April 6, 2010, Rhapsody officially declared its independence from RealNetworks. Downloaded files come with restrictions on their use, enforced by Helix, Rhapsody's version...

     supports the RealAudio AAC codec, in addition to offering subscription tracks encoded with AAC.
  • XBMC (XBox Media Center) supports both AAC (LC and HE) on modified Xbox
    Xbox
    The Xbox is a sixth-generation video game console manufactured by Microsoft. It was released on November 15, 2001 in North America, February 22, 2002 in Japan, and March 14, 2002 in Australia and Europe and is the predecessor to the Xbox 360. It was Microsoft's first foray into the gaming console...

     game-consoles.
  • XMMS
    XMMS
    The X Multimedia System is a free audio player for Unix-like systems.-History:XMMS was originally written as X11Amp by Peter and Mikael Alm in November 1997. The player was made to resemble Winamp, which was first released in May that year. As such, XMMS has supported Winamp 2 "classic" skins...

     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) or MP4-contained AAC streamed over HTTP using the SHOUTcast
SHOUTcast
SHOUTcast is cross-platform proprietary software for streaming media over the Internet. The software, developed by Nullsoft , allows digital audio content, primarily in MP3 or HE-AAC format, to be broadcast to and from media player software, enabling the creation of Internet radio "stations"...

 protocol. Plug-ins for Winamp and foobar2000 enable the creation of such streams.

Nero Digital Audio


In May 2006, Nero AG
Nero AG
Nero is a global computer software company headquartered in Karlsbad, Germany. It is perhaps most well-known for its burning software, Nero Burning ROM.-History:The company was founded as Ahead Software GmbH in 1995 by Richard Lesser....

 released an AAC encoding tool free of charge, Nero Digital Audio (Nero AAC Codec), which is capable of encoding LC-AAC, HE-AAC and HE-AAC v2 streams. The tool is a Command Line Interface tool only. A separate utility is also included to decode to PCM WAV
WAV
Waveform Audio File Format , is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs...

.

Various tools including the foobar2000
Foobar2000
foobar2000 is a freeware audio player for Windows developed by Peter Pawlowski, a former freelance contractor for Nullsoft. It is known for its highly modular design and extensive SDK which allows third-party developers to do such things as completely replace the interface...

 audio player, MediaCoder
MediaCoder
MediaCoder is a transcoding program for Microsoft Windows. It has been developed by Stanley Huang since 2005.MediaCoder uses various open source audio and video codecs, among several proprietary codecs and tools to transcode different audio/video formats and has many extra features...

, MeGUI encoding front end and dBpoweramp can provide a GUI
Gui
Gui or guee is a generic term to refer to grilled dishes in Korean cuisine. These most commonly have meat or fish as their primary ingredient, but may in some cases also comprise grilled vegetables or other vegetarian ingredients. The term derives from the verb, "gupda" in Korean, which literally...

 for this encoder.

FAAC and FAAD2


FAAC
FAAC
FAAC or Freeware Advanced Audio Coder is a software project which includes the AAC encoder FAAC and decoder FAAD2. It supports MPEG-2 AAC as well as MPEG-4 AAC. It supports several MPEG-4 Audio object types , file formats , multichannel and gapless encoding/decoding and MP4 metadata tags...

 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
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

, FAAC is not free software.

FFmpeg


FFmpeg
FFmpeg
FFmpeg is a free software project that produces libraries and programs for handling multimedia data. The most notable parts of FFmpeg are libavcodec, an audio/video codec library used by several other projects, libavformat, an audio/video container mux and demux library, and the ffmpeg command line...

's libavcodec
Libavcodec
libavcodec is a free software/open source LGPL-licensed library of codecs for encoding and decoding video and audio data. Same name but incompatible libraries are provided from both FFmpeg project and Libav project....

 library contains free software codecs for both encoding and decoding AAC (encoding is experimental).

See also

  • Comparison of audio codecs
    Comparison of audio codecs
    The following tables compare general and technical information for a variety of audio formats and audio compression formats. For listening tests comparing the perceived audio quality of audio formats and codecs, see the article Codec listening test....

  • AAC-LD
    AAC-LD
    The MPEG-4 Low Delay Audio Coder is audio compression format 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 format...

  • MPEG-4 Part 14
    MPEG-4 Part 14
    MPEG-4 Part 14 or MP4 is a multimedia container format standard specified as a part of MPEG-4. It is most commonly used to store digital video and digital audio streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images...

     (container format)
  • Vorbis
    Vorbis
    Vorbis is a free software / open source project headed by the Xiph.Org Foundation . The project produces an audio format specification and software implementation for lossy audio compression...


External links

  • Fraunhofer MPEG-2 AAC Information
  • AudioCoding.com – home of FAAC and FAAD2
  • Official MPEG web site
  • AAC improvements and extensions (2004)
  • RFC 3016 - RTP Payload Format for MPEG-4 Audio/Visual Streams
  • RFC 3640 - RTP Payload Format for Transport of MPEG-4 Elementary Streams
  • RFC 4281 - The Codecs Parameter for "Bucket" Media Types
  • RFC 4337 - MIME Type Registration for MPEG-4