Difference between revisions of "Advanced Audio Coding"

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See also [[Understanding AAC]].
See also [[Understanding AAC]].


== Extensions ==
== Common AAC Flavors ==
 
=== MPEG-2 AAC-LC ===
The basic subset of AAC that most other flavors and profiles are based on.
 
=== The AAC Profile (MPEG-4 AAC-LC) ===
MPEG-2 AAC-LC plus a Perceptual Noise Substitution (PNS) tool.
 
=== The HE-AAC Profile (v1 and v2) ===
 
HE-AAC (also known as by the [[Dolby Laboratories|Dolby]] trade name [http://www.codingtechnologies.com/products/aacPlus.htm aacPlus]) is MPEG-4 AAC-LC + [[Spectral Band Replication|SBR (Spectral Band Replication)]] and HE-AAC v2 (aacPlus v2) is MPEG-4 AAC-LC + SBR + [http://www.codingtechnologies.com/products/paraSter.htm PS (Parametric Stereo)]. Standard AAC-LC decoders can decode HE-AAC encoded files/streams but without SBR and PS you do not get the full quality.


=== HE-AAC ===
=== MPEG-2/4 AAC Main ===
MPEG-2/4 AAC-LC plus a computationally intensive, intra-channel, inter-frame frequency domain prediction tool. The details of the prediction tool are only given in ISO/IEC 13818-7 not in ISO/IEC 14496-4. This flavor is rarely seen in the wild.


HE-AAC (also known as by the [[Dolby Laboratories|Dolby]] trade name [http://www.codingtechnologies.com/products/aacPlus.htm aacPlus]) is AAC-LC + [[Spectral Band Replication|SBR (Spectral Band Replication)]] and HE-AAC v2 (aacPlus v2) is LC-AAC + SBR + [http://www.codingtechnologies.com/products/paraSter.htm PS (Parametric Stereo)]. Standard AAC-LC decoders can decode HE-AAC encoded files/streams but without SBR and PS you do not get the full quality.
=== MPEG-4 AAC LTP ===
MPEG-4 AAC-LC plus a less computationally intensive frequency domain prediction tool. This flavor is rarely seen in the wild. Despite being an MPEG-4 only flavor it can be embedded in an ADTS stream.  


* See also
* See also
** [[MP3#mp3PRO|MP3PRO]] that also uses SBR.
** [[MP3#mp3PRO|MP3PRO]] that also uses SBR.
** [http://www.mpegsurround.com MPEG Surround] that can used for all audio but especially MP3/mp3PRO and AAC/aacPlus. [http://www.codingtechnologies.com/products/mpgsrnd.htm MPEG Surround technology] share similar characteristics with [http://www.codingtechnologies.com/products/sbr.htm SBR (Spectral Band Replication)] and [http://www.codingtechnologies.com/products/paraSter.htm PS (Parametric Stereo)], which [[MP3#mp3PRO|MP3PRO]] and AAC+ decoders also use. [http://www.divx.com DivX Inc.] is one company that uses MPEG Surround technology to achieve 5.1 channel surround sound in smaller files.
** [http://www.mpegsurround.com MPEG Surround] that can used for all audio but especially MP3/mp3PRO and AAC/aacPlus. [http://www.codingtechnologies.com/products/mpgsrnd.htm MPEG Surround technology] share similar characteristics with [http://www.codingtechnologies.com/products/sbr.htm SBR (Spectral Band Replication)] and [http://www.codingtechnologies.com/products/paraSter.htm PS (Parametric Stereo)], which [[MP3#mp3PRO|MP3PRO]] and AAC+ decoders also use. [http://www.divx.com DivX Inc.] is one company that uses MPEG Surround technology to achieve 5.1 channel surround sound in smaller files.
== Extensions ==


=== GAIN headers ===
=== GAIN headers ===

Revision as of 11:01, 17 February 2009

Specification and reference source links.

Implementations with source code:

Other Notable Implementations:

Usually stored in an MP4 container.

See also Understanding AAC.

Common AAC Flavors

MPEG-2 AAC-LC

The basic subset of AAC that most other flavors and profiles are based on.

The AAC Profile (MPEG-4 AAC-LC)

MPEG-2 AAC-LC plus a Perceptual Noise Substitution (PNS) tool.

The HE-AAC Profile (v1 and v2)

HE-AAC (also known as by the Dolby trade name aacPlus) is MPEG-4 AAC-LC + SBR (Spectral Band Replication) and HE-AAC v2 (aacPlus v2) is MPEG-4 AAC-LC + SBR + PS (Parametric Stereo). Standard AAC-LC decoders can decode HE-AAC encoded files/streams but without SBR and PS you do not get the full quality.

MPEG-2/4 AAC Main

MPEG-2/4 AAC-LC plus a computationally intensive, intra-channel, inter-frame frequency domain prediction tool. The details of the prediction tool are only given in ISO/IEC 13818-7 not in ISO/IEC 14496-4. This flavor is rarely seen in the wild.

MPEG-4 AAC LTP

MPEG-4 AAC-LC plus a less computationally intensive frequency domain prediction tool. This flavor is rarely seen in the wild. Despite being an MPEG-4 only flavor it can be embedded in an ADTS stream.

Extensions

GAIN headers

See http://mp3gain.sourceforge.net and MP3 GAIN header.