High-Efficiency Advanced Audio Coding
High-Efficiency Advanced Audio Coding (HE-AAC) is an audio coding format for lossy data compression of 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. The usage profile HE-AAC v1 uses spectral band replication (SBR) to enhance the modified discrete cosine transform (MDCT) compression efficiency in the frequency domain.[3] The usage profile HE-AAC v2 couples SBR with Parametric Stereo (PS) to further enhance the compression efficiency of stereo signals.
"EAAC" redirects here. For the airline, see European Aviation Air Charter.Filename extensions
audio/aac
audio/aacp
audio/3gpp
audio/3gpp2
audio/mp4
Audio compression format
MPEG-4 Part 14, 3GP and 3G2, ISO base media file format, Audio Data Interchange Format (ADIF), Audio Data Transport Stream (ADTS)
HE-AAC is used in digital radio standards like HD Radio,[4] DAB+ and Digital Radio Mondiale.
History[edit]
The progenitor of HE-AAC was developed by Coding Technologies by combining MPEG-2 AAC-LC with a proprietary mechanism for spectral band replication (SBR), to be used by XM Radio for their satellite radio service. Subsequently, Coding Technologies submitted their SBR mechanism to MPEG as a basis of what ultimately became HE-AAC.
HE-AAC v1 was standardized as a profile of MPEG-4 Audio in 2003 by MPEG and published as part of the ISO/IEC 14496-3:2001/Amd 1:2003[5] specification.
The HE-AAC v2 profile was standardized in 2006 as per ISO/IEC 14496-3:2005/Amd 2:2006.[1][6]
Parts of the HE-AAC specification had previously been standardized and published by various bodies in
3GPP TS 26.401
,[7]
ETSI TS 126 401 V6.1.0
,[8]
ISO/IEC 14496-3:2001/Amd.1:2003 and
ISO/IEC 14496-3:2001/Amd 2:2004.
[9]
At the time, Coding Technologies had already begun using the trade names AAC+ and aacPlus for what is now known as HE-AAC v1, and aacPlus v2 and eAAC+ for what is now known as HE-AAC v2.
Perceived quality[edit]
Testing indicates that material decoded from 64 kbit/s HE-AAC does not quite have similar audio quality to material decoded from MP3 at 128 kbit/s using high quality encoders.[10][11][12][13] 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 HE-AAC v2 provide "Good" audio quality for music at low bit rates (e.g., 24 kbit/s).
In 2011, a public listening test[14] comparing the two best-rated HE-AAC encoders at the time to Opus and Ogg Vorbis indicated that Opus had statistically significant superiority at 64 kbit/s over all other contenders, and second-ranked Apple's implementation of HE-AAC as statistically superior to both Ogg Vorbis and Nero HE-AAC, 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]
Orban Opticodec-PC Streaming and File Encoders were the first commercially available encoders supporting AAC-LC/HE-AAC back in 2003. They are now deprecated and replaced with StreamS Encoders from StreamS/Modulation Index with many more features, including support xHE-AAC/Unified Speech and Audio Coding. They are now in use at some of the largest content providers, and are considered to be the standard of the industry for live encoding.
Sony supports HE-AAC encoding since SonicStage version 4.
iTunes 9 supports HE-AAC encoding and playback.[15][16]
Nero has released a free-of-charge command line HE-AAC encoder, Nero AAC Codec,[17] 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 macOS as well as Windows.
The 3GPP consortium released source code of a reference HE-AACv2 encoder that appears to offer competitive quality.[18]
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.[19]
XLD, a macOS 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 and v2 encoders are provided by the Fraunhofer FDK AAC library in Android 4.1 and later versions.[20]
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 and SonicStage.
The Nero AAC Codec supports decoding HE and HEv2 AAC.
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.
Promotion aspects[edit]
Commercial trademarks and labeling[edit]
HE-AAC is marketed under the trademark aacPlus by Coding Technologies and under the trademark Nero Digital 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[27] 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.[28] Unlike the MP3 format before April 23, 2017,[29] content owners are not required to pay license fees to distribute content in HE-AAC.