High-Efficiency Advanced Audio Coding

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Not to be confused with MPEG-4 SLS, which is branded HD-AAC.
High-Efficiency Advanced Audio Coding
Filename extension .m4a
.aac
.mp4
Internet media type audio/aacp, audio/3gpp, audio/3gpp2
Developed by ISO
Type of format Audio compression format
Contained by 3GP, MP4, .dvb, etc.
Extended from AAC
Standard ISO/IEC 14496-3
Hierarchical structure of AAC Profile, HE-AAC Profile and HE-AAC v2 Profile, and compatibility between them. The HE-AAC Profile decoder is fully capable of decoding any AAC Profile stream. Similarly the HE-AAC v2 decoder can handle all HE-AAC Profile streams as well as all AAC Profile streams. Based on the MPEG-4 Part 3 technical specification.[1]
Evolution from MPEG-2 AAC LC (Low Complexity) Profile and MPEG-4 AAC LC Object Type to HE-AACv2 Profile.[2]

High-Efficiency Advanced Audio Coding (HE-AAC) is a lossy data compression scheme for digital audio defined as an MPEG-4 Audio profile in ISO/IEC 14496-3. It is an extension of Low Complexity AAC (AAC LC) optimized for low-bitrate applications such as streaming audio. HE-AAC version 1 profile (HE-AAC v1) uses spectral band replication (SBR) to enhance the compression efficiency in the frequency domain. HE-AAC version 2 profile (HE-AAC v2) couples SBR with Parametric Stereo (PS) to enhance the compression efficiency of stereo signals. It is a standardized and improved version of the AACplus codec.

HE-AAC is used in digital radio standards like DAB+ and Digital Radio Mondiale.

History[edit]

The progenitor of HE-AAC was developed by Coding Technologies under the trade name CT-aacPlus. CT-aacPlus combined MPEG-2 AAC LC with the Coding Technologies invented spectral band replication (SBR). CT-aacPlus is the codec used by XM Radio for their satellite radio service. Subsequently, Coding Technologies submitted their SBR to MPEG as a basis of HE-AAC.

HE-AAC version 1 was standardized as a profile of MPEG-4 Audio in 2003 by MPEG and published as part of MPEG-4 in document ISO/IEC 14496-3:2001/Amd 1:2003.[3] The HE-AAC version 2 profile was standardized in 2006 as ISO/IEC 14496-3:2005/Amd 2:2006.[1][4] A parametric stereo coding tool used in HE-AAC v2 was standardized in 2004 by MPEG and published in document ISO/IEC 14496-3:2001/Amd 2:2004.[5]

HE-AAC version 2 was also standardized under the name Enhanced aacPlus by 3GPP for 3G UMTS multimedia services in September 2004 (3GPP TS 26.401). It is based on the AAC LC, SBR and Parametric Stereo coding tools defined in the MPEG-4 Audio standard (and it refers to ISO/IEC 14496-3:2001/Amd.1:2003 - Bandwidth Extension, ISO/IEC 14496-3:2001/Amd.2:2004 - Parametric Coding for High Quality Audio, ISO/IEC 14496-3:2001 and ISO/IEC 14496-3:2001/Amd.1:2003/DCOR1). In addition it includes further tools such as error concealment, spline resampler, and stereo-to-mono downmix.[6] It was also published by ETSI as TS 126 401 V6.1.0 in December 2004.[7]

Prior to the standardization of HE AAC v2 by MPEG, Coding Technologies submitted the combination of HE-AAC v1 coupled with Parametric Stereo under the name Enhanced AAC+. As a result, aacPlus v2 and eAAC+ are now common trade names that refer to HE-AAC v2. AAC+ and aacPlus are common trade names that refer to HE-AAC v1.

Perceived quality[edit]

Scientific testing by the European Broadcasting Union has indicated that HE-AAC at 48 kbit/s was ranked as "Excellent" quality using the MUSHRA scale.[8] MP3 in the same testing received a score less than half that of HE-AAC and was ranked "Poor" using the MUSHRA scale. Data from this testing also indicated that some individuals confused 48 kbit/s encoded material with an uncompressed original.

Testing indicates that material decoded from 64 kbit/s HE-AAC does not yet have similar audio quality to material decoded from MP3 at 128 kbit/s using high quality encoders.[9][10][11][12] The test, taking bitrate distribution and RMSD into account, is a tie between MP3pro, HE AAC and Ogg Vorbis.

Further controlled testing by 3GPP during their revision 6 specification process indicates that HE-AAC and its derivative MPEG-4 HE-AAC v2 provide "Good" audio quality for music at low bit rates (e.g., 24 kbit/s).

A 2011 Public Listening Test[13] comparing the two best-rated HE AAC encoders at that time to Ogg Vorbis and Opus, indicated statistically significant superiority at 64 kbit/s for Opus over all other contenders, with Apple HE AAC ranked second and statistically superior to both Nero HE AAC and Ogg Vorbis which were tied for third place.

MPEG-2 and MPEG-4 AAC LC decoders without SBR support will decode the AAC LC part of the audio, resulting in audio output with only half the sampling frequency, thereby reducing the audio bandwidth. This usually results in the high-end, or treble, portion of the audio signal missing from the audio product.

Support[edit]

Encoding[edit]

Sony supports HE-AAC encoding since SonicStage version 4.

iTunes 9 supports HE-AAC encoding and playback.[14][15]

Nero has released a free-of-charge command line HE-AAC encoder,[16] and also supports HE-AAC inside the Nero software suite.

Sorenson Media’s Squeeze Compression Suite includes an HE-AACv1 encoder and is available for Mac OS X as well as Windows.

The 3GPP consortium released source code of a reference HE-AACv2 encoder that appears to offer competitive quality.[17]

Die Plattenkiste and Winamp Pro also supports ripping music to HE-AAC. Using a transcoding plugin for Winamp's media library, any file can be transcoded to HE-AAC.[18]

XLD, an OS X audio encoding program, offers encoding from any of its supported formats to HE-AAC.

Nokia PC Suite may encode audiofiles to eAAC+ format before transmitting them to mobile phone.

HE-AAC v1 encoders are provided in Android 4.1 and later versions.[19]

Decoding[edit]

HE-AAC is supported in the open source FAAD/FAAD2 decoding library and all players incorporating it, such as VLC media player, Winamp, foobar2000, Audacious Media Player, SonicStage and Die Plattenkiste.

HE-AAC is also used by AOL Radio and Pandora Radio clients to deliver high-fidelity music at low bitrates.

iTunes 9.2 and iOS 4 include full decoding of HE-AAC v2 parametric stereo streams.

  • iTunes 9 thru 9.1, iPhone OS 3.1 and Fall 2009 iPods have support for HE-AAC playback for version 1 with no parametric stereo.
  • Older versions of Apple iTunes, iPod Touch, and iPhone will play HE-AAC files at reduced fidelity because they ignore the spectral-band replication and parametric stereo information, instead playing them as though they were standard AAC-LC files without the high-frequency, or "treble," information that is only present in the SBR part of the signal.[citation needed] These will report the track length as twice its actual length.[citation needed]

Dolby released Dolby Pulse decoders and encoders in September 2008. HE-AAC v2 is the core of Dolby Pulse so files and streams encoded in Dolby Pulse will playback on AAC, HE-AAC v1 and v2 decoders. Conversely files and streams encoded in AAC, HE-AAC v1 or v2 will playback on Dolby Pulse decoders.

Dolby Pulse provides the following additional capabilities beyond HE-AAC v2:

  • Ability to intelligently generate and insert reversible loudness normalization and dynamic range metadata into the encoded file/stream; this metadata can then be used to optimize the playback experience based on application and/or device.
  • Ability to insert custom metadata into the encoded file, and extract this metadata on playback

Dolby has additionally released a PC decoder as an SDK suitable for integration into PC applications requiring Dolby Pulse, HE-AAC or AAC playback capabilities.

HE-AAC v2 decoders are provided in all versions of Android.[19]

Clients[edit]

Promotion aspects[edit]

Commercial trademarks and labeling[edit]

HE-AAC is marketed under the trademark aacPlus(tm) by Coding Technologies and under the trademark Nero Digital(tm) by Nero AG. Sony Ericsson, Nokia and Samsung use AAC+ to label support for HE AAC v1 and eAAC+ to label support for HE-AAC v2 on their phones. Motorola uses AAC+ to indicate HE AAC v1 and "AAC+ Enhanced" to indicate HE AAC v2.

Licensing and patents[edit]

Companies holding patents for HE AAC have formed a patent pool administered by Via Licensing Corporation [22] to provide a single point of license for product makers.

Patent licenses are required for end-product companies that make hardware or software products that include HE AAC encoders and/or decoders.[23] Unlike the MP3 format,[24] content owners are not required to pay license fees to distribute content in HE AAC.

Standards[edit]

HE-AAC profile was first standardized in ISO/IEC 14496-3:2001/Amd 1:2003.[3] HE-AAC v2 profile (HE-AAC with Parametric Stereo) was first specified in ISO/IEC 14496-3:2005/Amd 2:2006.[1][4][25] The Parametric Stereo coding tool used by HE-AAC v2 was standardized in 2004 and published as ISO/IEC 14496-3:2001/Amd 2:2004.[5][6]

The current version of the MPEG-4 Audio (including HE-AAC standards) is published in ISO/IEC 14496-3:2009.

Enhanced aacPlus is required audio compression format in 3GPP technical specifications for 3G UMTS multimedia services and should be supported in IP Multimedia Subsystem (IMS), Multimedia Messaging Service (MMS), Multimedia Broadcast/Multicast Service (MBMS) and Transparent end-to-end Packet-switched Streaming Service (PSS).[26][27][28][29] HE-AAC version 2 was standardized under the name Enhanced aacPlus by 3GPP for 3G UMTS multimedia services in September 2004 (3GPP TS 26.401).[30]

HE-AAC and HE-AAC v2 audio coding for DVB applications is standardized by TS 101 154.[31][32] AacPlus v2 by Coding Technologies[33] is also standardized by the ETSI as TS 102 005 for Satellite services to Handheld devices (DVB-SH) below 3 GHz.

In December 2007, Brazil started broadcasting terrestrial DTV standard called International ISDB-Tb that implements video coding H.264 with audio AAC LC on main program (single or multi) and video H.264 with audio HE-AACv2 in the 1Seg mobile sub-program.

Versions[edit]

The following is the summary of the different versions of HE-AAC:

Version Common trade names Codec feature Standards
HE-AAC v1 aacPlus v1, eAAC, AAC+, CT-aacPlus AAC LC + SBR ISO/IEC 14496-3:2001/Amd 1:2003
HE-AAC v2 aacPlus v2, eAAC+, AAC++, Enhanced AAC+ AAC LC + SBR + PS ISO/IEC 14496-3:2005/Amd 2:2006

See also[edit]

References[edit]

  1. ^ a b c ISO/IEC JTC1/SC29/WG11/N7016 (2005-01-11), Text of ISO/IEC 14496-3:2001/FPDAM 4, Audio Lossless Coding (ALS), new audio profiles and BSAC extensions (DOC), retrieved 2009-10-09 
  2. ^ Fraunhofer IIS, MPEG-4 Audio and Video Technology (PDF), retrieved 2009-10-15 [dead link]
  3. ^ a b ISO (2003). "Bandwidth extension, ISO/IEC 14496-3:2001/Amd 1:2003". ISO. Retrieved 2009-10-13. 
  4. ^ a b ISO (2006). "Audio Lossless Coding (ALS), new audio profiles and BSAC extensions, ISO/IEC 14496-3:2005/Amd 2:2006". ISO. Retrieved 2009-10-13. 
  5. ^ a b ISO (2004). "Parametric coding for high-quality audio, ISO/IEC 14496-3:2001/Amd 2:2004". ISO. Retrieved 2009-10-13. 
  6. ^ a b 3GPP (2004-09-30). "3GPP TS 26.401 V6.0.0 (2004-09), General Audio Codec audio processing functions; Enhanced aacPlus General Audio Codec; General Description (Release 6)" (DOC). 3GPP. Retrieved 2009-10-13. 
  7. ^ 3GPP (2005-01-04). "ETSI TS 126 401 V6.1.0 (2004-12) - Universal Mobile Telecommunications System (UMTS); General audio codec audio processing functions; Enhanced aacPlus general audio codec; General description (3GPP TS 26.401 version 6.1.0 Release 6)". 3GPP. Retrieved 2009-10-13. 
  8. ^ http://tech.ebu.ch/docs/techreview/trev_305-moser.pdf
  9. ^ Results of 64kbit/s Listening Test
  10. ^ Multiformat Listening Test @ 48 kbps - FINISHED - Hydrogenaudio Forums
  11. ^ 80 kbps personal listening test (summer 2005) - Hydrogenaudio Forums
  12. ^ - MP3 - WMA - AAC - OGG - qualité à 96 kbps (évaluation) - Traitement Audio - Video & Son - FORUM HardWare.fr
  13. ^ 64kbit/sec stereo multiformat listening test —unofficial results page
  14. ^ http://www.apple.com/itunes/features/#importing
  15. ^ http://www.apple.com/itunes/features/#radio
  16. ^ "Nero AAC Codec". Retrieved 2009-11-23. 
  17. ^ Bouvigne, Gabriel (2006-03-20). "48kbps AAC public test results". MP3'Tech. Retrieved 2008-09-05. 
  18. ^ Winamp Transcoder
  19. ^ a b "Supported Media Formats". Google. Retrieved 2013-10-10. 
  20. ^ Adobe HD video: Supported technologies
  21. ^ Adobe bringing HD video, high quality audio to Flash using H.264, AAC (iPhone Flash support?) — MacDailyNews
  22. ^ Via Licensing Corporation
  23. ^ AAC Licensing FAQ
  24. ^ Thomson. "Thomson/FhG MP3 Licensing". 
  25. ^ Mihir Mody (2005-06-06). "Audio compression gets better and more complex". Embedded.com. Retrieved 2009-10-13. 
  26. ^ ETSI (2009-04) ETSI TS 126 234 V8.2.0 (2009-04); 3GPP TS 26.234; Transparent end-to-end Packet-switched Streaming Service (PSS); Protocols and codecs Page 58. Retrieved on 2009-06-02.
  27. ^ ETSI (2009-01) ETSI TS 126 140 V8.0.0 (2009-01); 3GPP TS 26.140; Multimedia Messaging Service (MMS); Media formats and codes Page 11. Retrieved on 2009-06-02.
  28. ^ ETSI (2009-01) ETSI TS 126 141 V8.0.0 (2009-01); 3GPP TS 26.141; IP Multimedia System (IMS) Messaging and Presence; Media formats and codecs Page 10. Retrieved on 2009-06-02.
  29. ^ 3GPP (2009). "ETSI TS 126 346 V8.3.0 (2009-06); 3GPP TS 26.346; Multimedia Broadcast/Multicast Service (MBMS); Protocols and codecs". ETSI. p. 85. Retrieved 2009-10-13. 
  30. ^ 3GPP (2004). "3GPP TS 26.401 - General audio codec audio processing functions; Enhanced aacPlus general audio codec; General description". 3GPP. Retrieved 2009-10-13. 
  31. ^ ETSI TS 101 154 v1.5.1: Specification for the use of Video and Audio Coding in Broadcasting Applications based on the MPEG-2 Transport Stream
  32. ^ ETSI (2009-03-31). "TS 101 154 version 1.9.1 - Digital Video Broadcasting (DVB); Specification for the use of Video and Audio Coding in Broadcasting Applications based on the MPEG-2 Transport Stream". ETSI. Retrieved 2009-10-13. 
  33. ^ http://www.codingtechnologies.com/products/assets/CT_aacPlus_whitepaper.pdf

External links[edit]