VideoLAN Wiki - User contributions [en]

MP4

2005-09-13T03:41:15Z

Ciscokid:

==MP4 = MPEG-4==

MP4 (*'''.mp4''') is the global file extension for the official container format defined in the MPEG-4 standard [[ISO 14496-14]].

==MP4 Filename Extensions==

* '''.mp4''': the only official extension; used for both audio and video files (and advanced content)
* '''.m4a''': introduced by Apple for aac/alac ''audio-only'' files.

NOTE: .m4a files can safely be renamed to .mp4 -- but the distinction between audio (m4a) and video (mp4) may be useful if you are going to share files, or if you tend to forget what files you have.

For complete details on MP4, see the following link:

*http://forum.doom9.org/showthread.php?s=&threadid=62723

User:Ciscokid

2005-09-11T09:02:12Z

Ciscokid:

other wikis:

* http://www.WoWWiki.com ([http://www.wowwiki.com/index.php?title=Special:Contributions&target=LAISREN Laisren])
* http://wikihost.org/wikis/ioswiki/ ([http://wikihost.org/wikis/ioswiki/programm/gebo.prg?name=user:cisco_kid cisco_kid])

User:Ciscokid

2005-09-11T08:58:58Z

Ciscokid:

other wikis:

* http://www.WoWWiki.com (Laisren)
* http://wikihost.org/wikis/IOSWiki (cisco_kid)

Dolby Digital

2005-09-11T08:57:28Z

Ciscokid: + cross-wiki to wikipedia:Dolby Digital

See

* [http://www.afterdawn.com/glossary/terms/dolby_digital.cfm http://www.afterdawn.com/glossary/terms/dolby_digital.cfm]
* [[wikipedia:Dolby Digital]]

AC3

2005-09-11T08:56:26Z

Ciscokid:

==AC3==

'''AC3''' is essentially the same thing as "AC-3" which is the same thing as "[[Dolby Digital]]". Sometimes also referred to as '''DD''', as in "DD 5.1" (short for "Dolby Digital for 5.1 channels").

Dolby's '''Audio Coding-3''' (AC-3) coding and compression technology was used by Dolby to create "Dolby Digital".
Dolby Digital is the brand name used for the AC-3 digital audio encoding system. First used in 1995 for movie theaters, Dolby Digital is now also considered the standard for high quality audio for home theaters.

The "AC3" name (without the hyphen) is often used to refer to any audio encoding which can be used for DVD encoding to match Dolby Digital's specification, but is not specifically licensed by Dolby.

==AC-3 VS==

AC-3 VS is Dolby '''V'''irtual '''S'''urround AC-3.

AC-3 VS uses the way you ears work to generate a surround sound feeling from a 2CH signal. This permits you to convert 5.1 AC3 audio that you might find on a DVD to AC-3 VS, dropping the birate to 192kbit/s while still maintaining a surround feeling and superior quality.

Dolby Digital

2005-09-11T08:42:27Z

Ciscokid:

See [http://www.afterdawn.com/glossary/terms/dolby_digital.cfm http://www.afterdawn.com/glossary/terms/dolby_digital.cfm]

AC3

2005-09-11T08:42:10Z

Ciscokid:

==AC3==

AC3 is the same thing as "[[Dolby Digital]]".

==AC-3== VS is Dolby Virtual Surround AC-3.

AC-3 VS uses the way you ears work to generate a surround sound feeling from a 2CH signal. This permits you to convert 5.1 AC3 audio that you might find on a DVD to AC-3 VS, dropping the birate to 192kbit/s while still maintaining a surround feeling and superior quality.

Codec

2005-09-11T08:36:58Z

Ciscokid: /* Audio Codecs */

[[wikipedia:Codec|Codec]] is short for coder/decoder.

==Video Codecs==

* [[MPEG-1]]
* [[MPEG-2]]
* [[MPEG-4]]
* [[Sorenson Video]]
* [[Windows Media Video]]
* [[Digital Video]]
* [[MJPEG]]
* [[H263]]
* [[H263]]
* [[H264]]
* [[Theora]]
* [[Indeo Video]]
* [[Real Media Video]]
* [[Cinepak]]
* [[On2 VP]]
* [[Flash Video]]
* [[Creative YUV]]
* [[Huffman YUV]]

==Audio Codecs==

* [[MPEG audio]]
* [[Dolby Digital]] ([[AC3]])
* [[DTS]]
* [[Vorbis]]
*[[ Speex]]
* [[AAC (Advanced Audio Coding)]]
* [[Windows Media Audio]]
* [[DV Audio]]
* [[FLAC]]
* [[LPCM]]
* [[ADPCM]]
* [[AMR]]
* [[QuickTime Audio]]
* [[Real Audio]]
* [[MACE]]
* [[MusePack]]

AAC (Advanced Audio Coding)

2005-09-11T08:34:43Z

Ciscokid: + redirect

#REDIRECT [[Advanced Audio Coding]]

.m4a

2005-09-11T08:04:04Z

Ciscokid:

==.m4a==
'''.m4a''' is the [[file extension]] attached to names of files using the '''M'''PEG-'''4 A'''udio standard. The normal extension for any MPEG-4 file is '''[[MPEG-4 Part 14|.mp4]]''', which is also mentioned in the MPEG-4 standard. The .m4a file extension has been popularized by Apple, which started using the .m4a file extension in their [[iTunes]] software and [[iPod]] music players to distinguish between MPEG-4 Video and Audio files. Currently, most software that supports MPEG-4 Audio also supports the .m4a extension. The most common type of .m4a files available are those using the AAC ([[Advanced Audio Coding]]) audio format, but other formats such as [[Apple Lossless]] and even [[mp3]] files may be put inside a .m4a container file. You can normally safely rename the file extension of a '''[[MPEG-4 Part 14|.mp4]]''' file containing only audio to .m4a or vice versa to get the file to properly play in your favorite audio player.

===Protected MPEG-4 Audio===
When these files have [[digital rights management]] (DRM) restrictions applied to them, their extension are changed to '''.m4p''', the ''p'' standing for ''protected''. Music files purchased from the [[iTunes Music Store]] have this extension.

===Audiobooks===
When they contain audiobook data, MPEG-4 files have a .m4b extension.

HE-AAC

2005-09-11T08:03:51Z

Ciscokid:

'''High Efficiency AAC aka HE-AAC aka aacPlus'''

'''aacPlus''' is a [[lossy data compression]] scheme for [[audio stream]]s. It is based on [[MPEG-4]], and combines three techniques: [[Advanced Audio Coding]] (AAC), [[Spectral Band Replication]] (SBR), and [[parametric stereo]] (PS).

aacPlus was standardized by the [[MPEG]] as part of the MPEG-4 Part 3 specification, under the '''High Efficiency AAC''' ('''HE-AAC''') name.

For details on the MPEG-4 Part 3 specification, see [http://en.wikipedia.org/wiki/MPEG-4_Part_3 wikipedia:MPEG-4_Part_3].

The [[codec]] can operate at very low bitrates and is good for [[Internet radio]] streaming. A 48 kilobit-per-second stream is considered to have higher quality than 128 [[kbit/s]] [[MP3]].

In HE-AAC, Spectral Band Replication (SBR) technology has been applied to AAC, and was incorporated into the standard to form High Efficiency AAC v1 (HE-AAC v1), (sometimes known as aacPlus v1).

Another recent introduction to AAC is Parametric Stereo ( aacPlus v2 or Enhanced aacPlus ). These technologies significantly improve the performance of AAC at lower bitrates, and are used, for example, in Digital Radio Mondiale .

====Support====
HE-AAC is supported in the [[free software|free]] [[FAAD2|FAAD2 decoding library]], and hence in many free players, and in [[Winamp]] and [[foobar2000]].

==See also==
*[[.m4a|.m4a file extension]] (the "mpeg4-audio" extenstion popularized by Apple iTunes)

===External links===
* [http://www.tuner2.com/ Tuner2.com] list of Internet radio stations using aacPlus
* [http://www.codingtechnologies.com/products/aacPlus.htm aacPlus explained]
* [http://www.audiocoding.com/ Open Source AAC codec] FAAC (encoder) and FAAD2 (decoder)

HE-AAC

2005-09-11T07:59:49Z

Ciscokid: link to MPEG-4, Part 3

'''High Efficiency AAC aka HE-AAC aka aacPlus'''

'''aacPlus''' is a [[lossy data compression]] scheme for [[audio stream]]s. It is based on [[MPEG-4]], and combines three techniques: [[Advanced Audio Coding]] (AAC), [[Spectral Band Replication]] (SBR), and [[parametric stereo]] (PS).

aacPlus was standardized by the [[MPEG]] as part of the MPEG-4 Part 3 specification, under the '''High Efficiency AAC''' ('''HE-AAC''') name.

For details on the MPEG-4 Part 3 specification, see [http://en.wikipedia.org/wiki/MPEG-4_Part_3 wikipedia:MPEG-4_Part_3].

(See also [[.mp4|.mp4 file extension]])

The [[codec]] can operate at very low bitrates and is good for [[Internet radio]] streaming. A 48 kilobit-per-second stream is considered to have higher quality than 128 [[kbit/s]] [[MP3]].

In HE-AAC, Spectral Band Replication (SBR) technology has been applied to AAC, and was incorporated into the standard to form High Efficiency AAC v1 (HE-AAC v1), (sometimes known as aacPlus v1).

Another recent introduction to AAC is Parametric Stereo ( aacPlus v2 or Enhanced aacPlus ). These technologies significantly improve the performance of AAC at lower bitrates, and are used, for example, in Digital Radio Mondiale .

====Support====
HE-AAC is supported in the [[free software|free]] [[FAAD2|FAAD2 decoding library]], and hence in many free players, and in [[Winamp]] and [[foobar2000]].

===External links===
* [http://www.tuner2.com/ Tuner2.com] list of Internet radio stations using aacPlus
* [http://www.codingtechnologies.com/products/aacPlus.htm aacPlus explained]
* [http://www.audiocoding.com/ Open Source AAC codec] FAAC (encoder) and FAAD2 (decoder)

Advanced Audio Coding

2005-09-11T07:56:21Z

Ciscokid: link to new HE-AAC entry

'''Advanced Audio Coding''' ('''AAC''') is a lossy data compression scheme intended for Streaming_audio audio streams .

==Overview==
AAC is a wideband audio coding algorithm that exploits two primary coding strategies to dramatically reduce the amount of data needed to convey high-quality digital audio. First, signal components that are perceptually irrelevant and can be discarded without a perceived loss of audio quality are removed. Next, redundancies in the coded audio signal are eliminated.

==Why AAC was designed==
AAC was designed as an improved-performance codec relative to MP3 (which was specified in MPEG-1 ) and MPEG-2 Part 3 (which is also known as "MPEG-2 Audio" or ISO ( International Organization for Standardization) / IEC (International Electrotechnical Commission) 13818-3).

==AAC ISO Standard==
AAC, which was first specified in the standard known formally as International Organization for Standardization|ISO / International Electrotechnical Commission|IEC 13818-7, was published in 1997 as a new "part" (distinct from ISO / IEC 13818-3) in the MPEG-2 family of international standards.

==Codec improvements==
The codec design was further improved in MPEG-4 Part 3 , known formally as ISO/IEC 14496-3, with the addition of Perceptual Noise Substitution (PNS) and a Long Term Predictor (LTP).

== Bifurcation s in the AAC standard==
Although the AAC codec specified in MPEG-2 Part 7 and the AAC specified in MPEG-4 Part 3 are somewhat different, they are both informally known as AAC (for clarity it is best to refer specifically either to MPEG-2 AAC or to MPEG-4 AAC ).

==AAC's improvements over MP3==
Some of its advances:
* Sample frequencies from 8 Hertz|Hz to 96 kiloherz|kHz (official MP3: 16 Hz to 48 kHz)
* Up to 48 channels
* Higher efficiency and simpler filterbank (hybrid → pure MDCT)
* Higher coding efficiency for stationary signals (blocksize: 576 → 1024 samples)
* Higher coding efficiency for transient signals (blocksize: 192 → 128 samples)
* Much better handling of frequencies above 16 kHz
* More flexible joint stereo (separate for every scale band)

What this all means to the listener is better and more stable quality than MP3 at equivalent or slightly lower bitrates.

==Modular Coding==
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 use for a particular application. The standard offers four default profiles:

*Low Complexity Profile (LC) - the simplest and most widely used and supported.
*Main Profile (MAIN), which expands upon LC with backwards prediction.
*Sample-rate Scalable (SRS), also called Scalable Sample Rate ( MPEG-4 AAC-SSR ).
*Long Term Prediction (LTP), added in MPEG-4, an improvement of the MAIN profile using a forward predictor with lower computational complexity

Depending on the AAC profile and the MP3 encoder, 96 kilobit|kbit /s AAC can give nearly the same or better perceptional quality as 128 kbit/s MP3.

==Products that support AAC==

===iTunes and iPod===

In April 2003, Apple Computer brought mainstream attention to AAC by announcing that its iTunes and iPod products would support songs in MPEG-4 AAC format (via a firmware update for older iPods), and that customers could download popular songs in a protected version of the format via the iTunes Music Store . AAC has now become so associated with Apple computer hardware|hardware and software that people are commonly of the mistaken belief that AAC expands to "Apple Audio Codec." Optionally, a digital rights management scheme (named FairPlay) can be employed in tandem.

Apple has added support for [[VBR]] encoding of AAC tracks in iTunes v5.0 (released 9/7/2005).

=== PSP ===

The Sony PSP (PlayStation Portable) has added AAC support with version 2.0 firmware update, which was released in August 2005 .

==Extensions==
* '''[[HE-AAC]] (High Efficiency AAC)''' (also the [[.m4a]] file extension)

== See also ==
*Audio data compression

== Some External links ==
* [http://www.apple.com/mpeg4/aac Apple's page on MPEG-4 AAC]
* [http://www.eetimes.com/story/OEG20011218S0048 EE Times article on AAC ]
* [http://www.iis.fraunhofer.de/amm/techinf/aac/ Fraunhofer MPEG-2 AAC Information ]
* [http://www.iso.org/ International Standards Organization ]
* [http://www.vialicensing.com/products/mpeg4aac/standard.html AAC Licensing ]
* [http://www.audiocoding.com/ Open Source AAC codec FAAC (encoder) and FAAD2 (decoder)]
* [http://www.rjamorim.com/test/ Roberto's public listening tests - blind, controlled listening tests of lossy compression formats including AAC]

Category:Audio codecs 
Category:Computer file formats

text on this page originally from [http://en.wikipedia.org/wiki/Advanced_Audio_Coding http://en.wikipedia.org/wiki/Advanced_Audio_Coding]

HE-AAC

2005-09-11T07:55:22Z

Ciscokid: new

'''High Efficiency AAC aka HE-AAC aka aacPlus'''

'''aacPlus''' is a [[lossy data compression]] scheme for [[audio stream]]s. It is based on [[MPEG-4]], and combines three techniques: [[Advanced Audio Coding]] (AAC), [[Spectral Band Replication]] (SBR), and [[parametric stereo]] (PS).

aacPlus was standardized by the [[MPEG]] under the '''High Efficiency AAC''' ('''HE-AAC''') name.

The [[codec]] can operate at very low bitrates and is good for [[Internet radio]] streaming. A 48 kilobit-per-second stream is considered to have higher quality than 128 [[kbit/s]] [[MP3]].

In HE-AAC, Spectral Band Replication (SBR) technology has been applied to AAC, and was incorporated into the standard to form High Efficiency AAC v1 (HE-AAC v1), (sometimes known as aacPlus v1).

Another recent introduction to AAC is Parametric Stereo ( aacPlus v2 or Enhanced aacPlus ). These technologies significantly improve the performance of AAC at lower bitrates, and are used, for example, in Digital Radio Mondiale .

====Support====
HE-AAC is supported in the [[free software|free]] [[FAAD2|FAAD2 decoding library]], and hence in many free players, and in [[Winamp]] and [[foobar2000]].

===External links===
* [http://www.tuner2.com/ Tuner2.com] list of Internet radio stations using aacPlus
* [http://www.codingtechnologies.com/products/aacPlus.htm aacPlus explained]
* [http://www.audiocoding.com/ Open Source AAC codec] FAAC (encoder) and FAAD2 (decoder)

Advanced Audio Coding

2005-09-11T07:43:49Z

Ciscokid:

'''Advanced Audio Coding''' ('''AAC''') is a lossy data compression scheme intended for Streaming_audio audio streams .

==Overview==
AAC is a wideband audio coding algorithm that exploits two primary coding strategies to dramatically reduce the amount of data needed to convey high-quality digital audio. First, signal components that are perceptually irrelevant and can be discarded without a perceived loss of audio quality are removed. Next, redundancies in the coded audio signal are eliminated.

==Why AAC was designed==
AAC was designed as an improved-performance codec relative to MP3 (which was specified in MPEG-1 ) and MPEG-2 Part 3 (which is also known as "MPEG-2 Audio" or ISO ( International Organization for Standardization) / IEC (International Electrotechnical Commission) 13818-3).

==AAC ISO Standard==
AAC, which was first specified in the standard known formally as International Organization for Standardization|ISO / International Electrotechnical Commission|IEC 13818-7, was published in 1997 as a new "part" (distinct from ISO / IEC 13818-3) in the MPEG-2 family of international standards.

==Codec improvements==
The codec design was further improved in MPEG-4 Part 3 , known formally as ISO/IEC 14496-3, with the addition of Perceptual Noise Substitution (PNS) and a Long Term Predictor (LTP).

== Bifurcation s in the AAC standard==
Although the AAC codec specified in MPEG-2 Part 7 and the AAC specified in MPEG-4 Part 3 are somewhat different, they are both informally known as AAC (for clarity it is best to refer specifically either to MPEG-2 AAC or to MPEG-4 AAC ).

==AAC's improvements over MP3==
Some of its advances:
* Sample frequencies from 8 Hertz|Hz to 96 kiloherz|kHz (official MP3: 16 Hz to 48 kHz)
* Up to 48 channels
* Higher efficiency and simpler filterbank (hybrid → pure MDCT)
* Higher coding efficiency for stationary signals (blocksize: 576 → 1024 samples)
* Higher coding efficiency for transient signals (blocksize: 192 → 128 samples)
* Much better handling of frequencies above 16 kHz
* More flexible joint stereo (separate for every scale band)

What this all means to the listener is better and more stable quality than MP3 at equivalent or slightly lower bitrates.

==Modular Coding==
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 use for a particular application. The standard offers four default profiles:

*Low Complexity Profile (LC) - the simplest and most widely used and supported.
*Main Profile (MAIN), which expands upon LC with backwards prediction.
*Sample-rate Scalable (SRS), also called Scalable Sample Rate ( MPEG-4 AAC-SSR ).
*Long Term Prediction (LTP), added in MPEG-4, an improvement of the MAIN profile using a forward predictor with lower computational complexity

Depending on the AAC profile and the MP3 encoder, 96 kilobit|kbit /s AAC can give nearly the same or better perceptional quality as 128 kbit/s MP3.

==Products that support AAC==

===iTunes and iPod===

In April 2003, Apple Computer brought mainstream attention to AAC by announcing that its iTunes and iPod products would support songs in MPEG-4 AAC format (via a firmware update for older iPods), and that customers could download popular songs in a protected version of the format via the iTunes Music Store . AAC has now become so associated with Apple computer hardware|hardware and software that people are commonly of the mistaken belief that AAC expands to "Apple Audio Codec." Optionally, a digital rights management scheme (named FairPlay) can be employed in tandem.

Apple has added support for [[VBR]] encoding of AAC tracks in iTunes v5.0 (released 9/7/2005).

=== PSP ===

The Sony PSP (PlayStation Portable) has added AAC support with version 2.0 firmware update, which was released in August 2005 .

==Extensions==
* High Efficiency AAC ( MPEG-4 HE-AAC, a.k.a. heaac) - Spectral Band Replication (SBR) technology has been applied to AAC, and was incorporated into the standard to form High Efficiency AAC v1, also known as aacPlus v1 . Another recent introduction to AAC is Parametric Stereo ( aacPlus v2 or Enhanced aacPlus ). These technologies significantly improve the performance of AAC at lower bitrates, and are used, for example, in Digital Radio Mondiale .

== See also ==
*Audio data compression
*''*.m4a ''' file extension (MPEG-4 Part 3)

== Some External links ==
* [http://www.apple.com/mpeg4/aac Apple's page on MPEG-4 AAC]
* [http://www.eetimes.com/story/OEG20011218S0048 EE Times article on AAC ]
* [http://www.iis.fraunhofer.de/amm/techinf/aac/ Fraunhofer MPEG-2 AAC Information ]
* [http://www.iso.org/ International Standards Organization ]
* [http://www.vialicensing.com/products/mpeg4aac/standard.html AAC Licensing ]
* [http://www.audiocoding.com/ Open Source AAC codec FAAC (encoder) and FAAD2 (decoder)]
* [http://www.rjamorim.com/test/ Roberto's public listening tests - blind, controlled listening tests of lossy compression formats including AAC]

Category:Audio codecs 
Category:Computer file formats

text on this page originally from [http://en.wikipedia.org/wiki/Advanced_Audio_Coding http://en.wikipedia.org/wiki/Advanced_Audio_Coding]

Advanced Audio Coding

2005-09-11T07:39:01Z

Ciscokid: /* iTunes and iPod */

'''Advanced Audio Coding''' ('''AAC''') is a lossy data compression scheme intended for Streaming_audio audio streams .

==Overview==
AAC is a wideband audio coding algorithm that exploits two primary coding strategies to dramatically reduce the amount of data needed to convey high-quality digital audio. First, signal components that are perceptually irrelevant and can be discarded without a perceived loss of audio quality are removed. Next, redundancies in the coded audio signal are eliminated.

==Why AAC was designed==
AAC was designed as an improved-performance codec relative to MP3 (which was specified in MPEG-1 ) and MPEG-2 Part 3 (which is also known as "MPEG-2 Audio" or ISO ( International Organization for Standardization) / IEC (International Electrotechnical Commission) 13818-3).

==AAC ISO Standard==
AAC, which was first specified in the standard known formally as International Organization for Standardization|ISO / International Electrotechnical Commission|IEC 13818-7, was published in 1997 as a new "part" (distinct from ISO / IEC 13818-3) in the MPEG-2 family of international standards.

==Codec improvements==
The codec design was further improved in MPEG-4 Part 3 , known formally as ISO/IEC 14496-3, with the addition of Perceptual Noise Substitution (PNS) and a Long Term Predictor (LTP).

== Bifurcation s in the AAC standard==
Although the AAC codec specified in MPEG-2 Part 7 and the AAC specified in MPEG-4 Part 3 are somewhat different, they are both informally known as AAC (for clarity it is best to refer specifically either to MPEG-2 AAC or to MPEG-4 AAC ).

==AAC's improvements over MP3==
Some of its advances:
* Sample frequencies from 8 Hertz|Hz to 96 kiloherz|kHz (official MP3: 16 Hz to 48 kHz)
* Up to 48 channels
* Higher efficiency and simpler filterbank (hybrid → pure MDCT)
* Higher coding efficiency for stationary signals (blocksize: 576 → 1024 samples)
* Higher coding efficiency for transient signals (blocksize: 192 → 128 samples)
* Much better handling of frequencies above 16 kHz
* More flexible joint stereo (separate for every scale band)

What this all means to the listener is better and more stable quality than MP3 at equivalent or slightly lower bitrates.

==Modular Coding==
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 use for a particular application. The standard offers four default profiles:

* Low Complexity Profile (LC) - the simplest and most widely used and supported.
* Main Profile (MAIN), which expands upon LC with backwards prediction.
* Sample-rate Scalable (SRS), also called Scalable Sample Rate ( MPEG-4 AAC-SSR ).
* Long Term Prediction (LTP), added in MPEG-4, an improvement of the MAIN profile using a forward predictor with lower computational complexity

Depending on the AAC profile and the MP3 encoder, 96 kilobit|kbit /s AAC can give nearly the same or better perceptional quality as 128 kbit/s MP3.

==Products that support AAC==

===iTunes and iPod===

In April 2003, Apple Computer brought mainstream attention to AAC by announcing that its Apple iTunes|iTunes and iPod products would support songs in MPEG-4 AAC format (via a firmware update for older iPods), and that customers could download popular songs in a protected version of the format via the iTunes Music Store . AAC has now become so associated with Apple computer hardware|hardware and software that people are commonly of the mistaken belief that AAC expands to "Apple Audio Codec." Optionally, a digital rights management scheme (named FairPlay) can be employed in tandem.

Apple has added support for VBR encoding of AAC tracks in iTunes v5.0 (released 9/7/2005).

=== PSP ===
PlayStation Portable|Sony PSP has added AAC support with version 2.0 firmware update, which was released in August 2005 .

==Extensions==
* High Efficiency AAC ( MPEG-4 HE-AAC ) - Spectral Band Replication|SBR technology has been applied to AAC, and was incorporated into the standard to form High Efficiency AAC v1, also known as aacPlus v1 . Another recent introduction to AAC is Parametric Stereo ( aacPlus v2 or Enhanced aacPlus ). These technologies significantly improve the performance of AAC at lower bitrates, and are used, for example, in Digital Radio Mondiale .

== See also ==
* Audio data compression
* ''' MPEG-4 Part 3#.m4a|*.m4a ''' file extension

== Some External links ==
* [http://www.apple.com/mpeg4/aac Apple's page on MPEG-4 AAC
* [http://www.eetimes.com/story/OEG20011218S0048 EE Times article on AAC
* [http://www.iis.fraunhofer.de/amm/techinf/aac/ Fraunhofer MPEG-2 AAC Information
* [http://www.iso.org/ International Standards Organization
* [http://www.vialicensing.com/products/mpeg4aac/standard.html AAC Licensing
* [http://www.audiocoding.com/ Open Source AAC codec FAAC (encoder) and FAAD2 (decoder)
* [http://www.rjamorim.com/test/ Roberto's public listening tests - blind, controlled listening tests of lossy compression formats including AAC

Category:Audio codecs
Category:Computer file formats

AAC

2005-09-11T07:23:59Z

Ciscokid: See Advanced Audio Coding

See [[Advanced Audio Coding]]

Advanced Audio Coding

2005-09-11T07:23:26Z

Ciscokid:

'''Advanced Audio Coding''' ('''AAC''') is a lossy data compression scheme intended for Streaming_audio audio streams .

==Overview==
AAC is a wideband audio coding algorithm that exploits two primary coding strategies to dramatically reduce the amount of data needed to convey high-quality digital audio. First, signal components that are perceptually irrelevant and can be discarded without a perceived loss of audio quality are removed. Next, redundancies in the coded audio signal are eliminated.

==Why AAC was designed==
AAC was designed as an improved-performance codec relative to MP3 (which was specified in MPEG-1 ) and MPEG-2 Part 3 (which is also known as "MPEG-2 Audio" or ISO ( International Organization for Standardization) / IEC (International Electrotechnical Commission) 13818-3).

==AAC ISO Standard==
AAC, which was first specified in the standard known formally as International Organization for Standardization|ISO / International Electrotechnical Commission|IEC 13818-7, was published in 1997 as a new "part" (distinct from ISO / IEC 13818-3) in the MPEG-2 family of international standards.

==Codec improvements==
The codec design was further improved in MPEG-4 Part 3 , known formally as ISO/IEC 14496-3, with the addition of Perceptual Noise Substitution (PNS) and a Long Term Predictor (LTP).

== Bifurcation s in the AAC standard==
Although the AAC codec specified in MPEG-2 Part 7 and the AAC specified in MPEG-4 Part 3 are somewhat different, they are both informally known as AAC (for clarity it is best to refer specifically either to MPEG-2 AAC or to MPEG-4 AAC ).

==AAC's improvements over MP3==
Some of its advances:
* Sample frequencies from 8 Hertz|Hz to 96 kiloherz|kHz (official MP3: 16 Hz to 48 kHz)
* Up to 48 channels
* Higher efficiency and simpler filterbank (hybrid → pure MDCT)
* Higher coding efficiency for stationary signals (blocksize: 576 → 1024 samples)
* Higher coding efficiency for transient signals (blocksize: 192 → 128 samples)
* Much better handling of frequencies above 16 kHz
* More flexible joint stereo (separate for every scale band)

What this all means to the listener is better and more stable quality than MP3 at equivalent or slightly lower bitrates.

==Modular Coding==
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 use for a particular application. The standard offers four default profiles:

* Low Complexity Profile (LC) - the simplest and most widely used and supported.
* Main Profile (MAIN), which expands upon LC with backwards prediction.
* Sample-rate Scalable (SRS), also called Scalable Sample Rate ( MPEG-4 AAC-SSR ).
* Long Term Prediction (LTP), added in MPEG-4, an improvement of the MAIN profile using a forward predictor with lower computational complexity

Depending on the AAC profile and the MP3 encoder, 96 kilobit|kbit /s AAC can give nearly the same or better perceptional quality as 128 kbit/s MP3.

==Products that support AAC==

===iTunes and iPod===
Image:Original iPod 5GB.jpg|thumbnail|right|50px|An iPod
In April 2003|April, 2003 , Apple Computer brought mainstream attention to AAC by announcing that its Apple iTunes|iTunes and iPod products would support songs in MPEG-4 AAC format (via a firmware update for older iPods), and that customers could download popular songs in a protected version of the format via the iTunes Music Store . AAC has now become so associated with Apple computer hardware|hardware and software that people are commonly of the mistaken belief that AAC expands to "Apple Audio Codec." Optionally, a digital rights management scheme (named FairPlay ) can be employed in tandem.

Apple has added support for VBR encoding of AAC tracks in iTunes v5.0 (released 9/7/2005).

=== PSP ===
PlayStation Portable|Sony PSP has added AAC support with version 2.0 firmware update, which was released in August 2005 .

==Extensions==
* High Efficiency AAC ( MPEG-4 HE-AAC ) - Spectral Band Replication|SBR technology has been applied to AAC, and was incorporated into the standard to form High Efficiency AAC v1, also known as aacPlus v1 . Another recent introduction to AAC is Parametric Stereo ( aacPlus v2 or Enhanced aacPlus ). These technologies significantly improve the performance of AAC at lower bitrates, and are used, for example, in Digital Radio Mondiale .

== See also ==
* Audio data compression
* ''' MPEG-4 Part 3#.m4a|*.m4a ''' file extension

== Some External links ==
* [http://www.apple.com/mpeg4/aac Apple's page on MPEG-4 AAC
* [http://www.eetimes.com/story/OEG20011218S0048 EE Times article on AAC
* [http://www.iis.fraunhofer.de/amm/techinf/aac/ Fraunhofer MPEG-2 AAC Information
* [http://www.iso.org/ International Standards Organization
* [http://www.vialicensing.com/products/mpeg4aac/standard.html AAC Licensing
* [http://www.audiocoding.com/ Open Source AAC codec FAAC (encoder) and FAAD2 (decoder)
* [http://www.rjamorim.com/test/ Roberto's public listening tests - blind, controlled listening tests of lossy compression formats including AAC

Category:Audio codecs
Category:Computer file formats

Advanced Audio Coding

2005-09-11T07:01:00Z

Ciscokid: from wikipedia (GNU Free Documentation License)

'''Advanced Audio Coding''' ('''AAC''') is a [[lossy data compression]] scheme intended for [[audio stream]]s.

==Overview==
AAC is a wideband audio coding algorithm that exploits two primary coding strategies to dramatically reduce the amount of data needed to convey high-quality digital audio. First, signal components that are perceptually irrelevant and can be discarded without a perceived loss of audio quality are removed. Next, redundancies in the coded audio signal are eliminated.

==Why AAC was designed==
AAC was designed as an improved-performance codec relative to [[MP3]] (which was specified in [[MPEG-1]]) and [[MPEG-2]] Part 3 (which is also known as "MPEG-2 Audio" or [[International Organization for Standardization|ISO]]/[[International Electrotechnical Commission|IEC]] 13818-3).

==AAC ISO Standard==
AAC, which was first specified in the standard known formally as [[International Organization for Standardization|ISO]]/[[International Electrotechnical Commission|IEC]] 13818-7, was published in 1997 as a new "part" (distinct from [[International Organization for Standardization|ISO]]/[[International Electrotechnical Commission|IEC]] 13818-3) in the [[MPEG-2]] family of [[international standard]]s.

==Codec improvements==
The codec design was further improved in [[MPEG-4 Part 3]], known formally as [[International Organization for Standardization|ISO]]/[[International Electrotechnical Commission|IEC]] 14496-3, with the addition of Perceptual Noise Substitution (PNS) and a Long Term Predictor (LTP).

==[[Bifurcation]]s in the AAC standard==
Although the AAC codec specified in [[MPEG-2]] Part 7 and the AAC specified in [[MPEG-4]] Part 3 are somewhat different, they are both informally known as AAC (for clarity it is best to refer specifically either to [[MPEG-2 AAC]] or to [[MPEG-4 AAC]]).

==AAC's improvements over MP3==
Some of its advances:
* Sample frequencies from 8 [[Hertz|Hz]] to 96 [[kiloherz|kHz]] (official MP3: 16 Hz to 48 kHz)
* Up to 48 channels
* Higher efficiency and simpler filterbank (hybrid → pure MDCT)
* Higher coding efficiency for stationary signals (blocksize: 576 → 1024 samples)
* Higher coding efficiency for transient signals (blocksize: 192 → 128 samples)
* Much better handling of frequencies above 16 kHz
* More flexible joint stereo (separate for every scale band)

What this all means to the listener is better and more stable quality than MP3 at equivalent or slightly lower bitrates.

==Modular Coding==
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 use for a particular application. The standard offers four default profiles:

* [[Low Complexity Profile]] (LC) - the simplest and most widely used and supported.
* Main Profile (MAIN), which expands upon LC with backwards prediction.
* [[Sample-rate Scalable]] (SRS), also called [[Scalable Sample Rate]] ([[MPEG-4 AAC-SSR]]).
* [[Long Term Prediction]] (LTP), added in MPEG-4, an improvement of the MAIN profile using a forward predictor with lower computational complexity

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

==Products that support AAC==

===iTunes and iPod===
[[Image:Original iPod 5GB.jpg|thumbnail|right|50px|An iPod]]
In [[April 2003|April, 2003]], [[Apple Computer]] brought mainstream attention to AAC by announcing that its [[Apple iTunes|iTunes]] and [[iPod]] products would support songs in MPEG-4 AAC format (via a [[firmware]] update for older iPods), and that customers could download popular songs in a protected version of the format via the [[iTunes Music Store]]. AAC has now become so associated with Apple [[computer hardware|hardware]] and [[software]] that people are commonly of the mistaken belief that AAC expands to "Apple Audio Codec." Optionally, a [[digital rights management]] scheme (named [[FairPlay]]) can be employed in tandem.

Apple has added support for [[VBR]] encoding of AAC tracks in iTunes v5.0 (released 9/7/2005).

=== PSP ===
[[PlayStation Portable|Sony PSP]] has added AAC support with version 2.0 firmware update, which was released in [[August 2005]].

==Extensions==
*[[High Efficiency AAC]] ([[MPEG-4 HE-AAC]]) - [[Spectral Band Replication|SBR]] technology has been applied to AAC, and was incorporated into the standard to form High Efficiency AAC v1, also known as [[aacPlus v1]]. Another recent introduction to AAC is [[Parametric Stereo]] ([[aacPlus v2]] or [[Enhanced aacPlus]]). These technologies significantly improve the performance of AAC at lower bitrates, and are used, for example, in [[Digital Radio Mondiale]].

== See also ==
* [[Audio data compression]]
* '''[[MPEG-4 Part 3#.m4a|*.m4a]]''' file extension

== Some External links ==
* [http://www.apple.com/mpeg4/aac Apple's page on MPEG-4 AAC]
* [http://www.eetimes.com/story/OEG20011218S0048 EE Times article on AAC]
* [http://www.iis.fraunhofer.de/amm/techinf/aac/ Fraunhofer MPEG-2 AAC Information]
* [http://www.iso.org/ International Standards Organization]
* [http://www.vialicensing.com/products/mpeg4aac/standard.html AAC Licensing]
* [http://www.audiocoding.com/ Open Source AAC codec] FAAC (encoder) and FAAD2 (decoder)
* [http://www.rjamorim.com/test/ Roberto's public listening tests] - blind, controlled listening tests of lossy compression formats including AAC

[[Category:Audio codecs]]
[[Category:Computer file formats]]