Difference between revisions of "Advanced Audio Coding"

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(→‎MPEG-2/4 AAC Main: Mention other Main features)
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*[[AAC Reference Software]]
*[[AAC Reference Software]]


Implementations with source code:
Usually stored in an [[MP4]] container.
 
See also [[Understanding AAC]].
 
== Implementations ==
 
=== With Source Code ===
*[[Google]] has opensourced Android, which includes an Apache 2.0 licensed aac decoder:  
*[[Google]] has opensourced Android, which includes an Apache 2.0 licensed aac decoder:  
**http://git.source.android.com/?p=platform/external/opencore.git;a=tree;f=codecs_v2/audio/aac/dec;hb=HEAD
**http://git.source.android.com/?p=platform/external/opencore.git;a=tree;f=codecs_v2/audio/aac/dec;hb=HEAD
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**http://www.audiocoding.com
**http://www.audiocoding.com


Other Notable Implementations:
=== Other Notables ===
*[[Nero]] has a well regarded freeware AAC encoder and decoder
*[[Nero]] has a well regarded freeware AAC encoder and decoder
**http://www.nero.com/enu/technologies-aac-codec.html
**http://www.nero.com/enu/technologies-aac-codec.html
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*[[Apple]] who popularized the format in its [[iTunes]] software has an encoders and decoders available in iTunes and [[QuickTime]]
*[[Apple]] who popularized the format in its [[iTunes]] software has an encoders and decoders available in iTunes and [[QuickTime]]
**http://www.apple.com/itunes
**http://www.apple.com/itunes
Usually stored in an [[MP4]] container.
See also [[Understanding AAC]].


== Common AAC Flavors ==
== Common AAC Flavors ==
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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 (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.
* See also
** [[MP3#mp3PRO|MP3PRO]] that also uses SBR.


=== MPEG-2/4 AAC Main ===
=== MPEG-2/4 AAC Main ===
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=== MPEG-4 AAC LTP ===
=== 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.  
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
** [[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.


== Extensions ==
== Extensions ==
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See http://mp3gain.sourceforge.net and [[MP3#GAIN (MP3Gain) header|MP3 GAIN header]].
See http://mp3gain.sourceforge.net and [[MP3#GAIN (MP3Gain) header|MP3 GAIN header]].
=== MPEG Surround ===
[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.





Revision as of 00:20, 23 February 2009

Specification and reference source links.

Usually stored in an MP4 container.

See also Understanding AAC.

Implementations

With Source Code

Other Notables

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.

  • See also

MPEG-2/4 AAC Main

MPEG-2/4 AAC-LC plus a computationally intensive, intra-channel, inter-frame frequency domain prediction tool. Additionally this profile adds relaxation to the maximum TNS filter size, and time domain coupling. 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.

MPEG Surround

MPEG Surround that can used for all audio but especially MP3/mp3PRO and AAC/aacPlus. MPEG Surround technology share similar characteristics with SBR (Spectral Band Replication) and PS (Parametric Stereo), which MP3PRO and AAC+ decoders also use. DivX Inc. is one company that uses MPEG Surround technology to achieve 5.1 channel surround sound in smaller files.