High-Efficiency Advanced Audio Coding
High-Efficiency Advanced Audio Coding 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 optimized for low-bitrate applications such as streaming audio. The usage profile AAC-HE v1 uses spectral band replication to enhance the modified discrete cosine transform compression efficiency in the frequency domain. The usage profile AAC-HE v2 couples SBR with Parametric Stereo to further enhance the compression efficiency of stereo signals.
AAC-HE is used in digital radio standards like HD Radio, DAB+ and Digital Radio Mondiale.
History
The progenitor of AAC-HE was developed by Coding Technologies by combining MPEG-2 AAC-LC with a proprietary mechanism for spectral band replication, 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 AAC-HE.AAC-HE 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 specification.
The AAC-HE v2 profile was standardized in 2006 as per ISO/IEC 14496-3:2005/Amd 2:2006.
Parts of the AAC-HE specification had previously been standardized and published by various bodies in
3GPP TS 26.401
ETSI TS 126 401 V6.1.0
ISO/IEC 14496-3:2001/Amd.1:2003 and
ISO/IEC 14496-3:2001/Amd 2:2004.
At the time, Coding Technologies had already begun using the trade names AAC+ and aacPlus for what is now known as AAC-HE v1, and aacPlus v2 and eAAC+ for what is now known as AAC-HE v2.
Perceived quality
Testing indicates that material decoded from 64 kbit/s AAC-HE does not quite have similar audio quality to material decoded from MP3 at 128 kbit/s using high quality encoders. The test, taking bitrate distribution and RMSD into account, is a tie between mp3PRO, AAC-HE and Ogg Vorbis.Further controlled testing by 3GPP during their revision 6 specification process indicates that AAC-HE and AAC-HE v2 provide "Good" audio quality for music at low bit rates.
In 2011, a public listening test comparing the two best-rated AAC-HE encoders at the time to Opus and Ogg Vorbis indicated statistically significant superiority at 64 kbit/s for Opus over all other contenders, and second-ranked Apple's implementation of AAC-HE as statistically superior to both Ogg Vorbis and Nero AAC-HE, 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
Encoding
Orban Opticodec-PC Streaming and File Encoders were the first commercially available encoders supporting AAC-LC/AAC-HE back in 2003. They are now deprecated and replaced with StreamS Encoders from StreamS/Modulation Index with many more features, including support xAAC-HE/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 AAC-HE encoding since SonicStage version 4.
iTunes 9 supports AAC-HE encoding and playback.
Nero has released a free-of-charge command line AAC-HE encoder, Nero AAC Codec, and also supports AAC-HE inside the Nero software suite.
Sorenson Media’s Squeeze Compression Suite includes an AAC-HEv1 encoder and is available for Mac OS X as well as Windows.
The 3GPP consortium released source code of a reference AAC-HEv2 encoder that appears to offer competitive quality.
and Winamp Pro also supports ripping music to AAC-HE. Using a transcoding plugin for Winamp's media library, any file can be transcoded to AAC-HE.
, an OS X audio encoding program, offers encoding from any of its supported formats to AAC-HE.
Nokia PC Suite may encode audiofiles to eAAC+ format before transmitting them to mobile phone.
AAC-HE v1 and v2 encoders are provided by the Fraunhofer FDK AAC library in Android 4.1 and later versions.
Decoding
AAC-HE 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 .The Nero AAC Codec supports decoding HE and HEv2 AAC.
AAC-HE 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 AAC-HE v2 parametric stereo streams.
- iTunes 9 thru 9.1, iPhone OS 3.1 and Fall 2009 iPods have support for AAC-HE playback for version 1 with no parametric stereo.
- Older versions of Apple iTunes, iPod Touch, and iPhone will play AAC-HE 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. These will report the track length as twice its actual length.
Dolby Pulse provides the following additional capabilities beyond AAC-HE 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
AAC-HE v2 decoders are provided in all versions of Android. Decoding is handled by Fraunhofer FDK AAC since Android version 4.1.
Clients
| Application | Platform | Description |
| AIMP | Windows | A Winamp-like alternative music player. |
| Adobe Flash Player | Windows, OS X, Chrome OS, Linux | Browser plug-in. Supports AAC+ from any RTMP source. Live streams wrapped in an ADTS container are not natively supported and have to be re-wrapped. |
| Amarok | Windows, Linux | Open-source music player. |
| Audacious Media Player | Windows, Linux | Open-source music player. |
| Linux, Android | Open-source music player. | |
| Windows | Freeware internet radio application. | |
| foobar2000 | Windows | Freeware music player. |
| OS X, iOS | Internet radio application. | |
| iOS | Internet radio application. | |
| Android | Internet radio player. | |
| iOS | Internet radio application. | |
| iTunes | Windows, OS X | Freeware music player. Pre-installed on Mac computers. |
| JetAudio | Windows, Android | Shareware media player. |
| MediaHuman Audio Converter | Windows, OS X | Freeware audio converter. |
| MPlayer | Windows, OS X and Linux | Open-source media player. |
| Mpv | Windows, OS X and Linux | Open-source media player. |
| Rockbox | Various portable media devices | Alternate firmware for various portable media-players, such as Apple iPod and Creative Zen. |
| QuickTime X | OS X | Media player pre-installed on OS X Snow Leopard or later. |
| RealPlayer | Windows, OS X, Linux, Android | Freemium media player. |
| Rhythmbox | Linux | Open-source music player. |
| OS X | Shareware internet radio application. | |
| Windows | Open-source internet radio application. | |
| iOS | Paidware internet radio player. | |
| Tunein radio | iOS, Android, Windows Phone, Blackberry | Internet radio player. |
| VLC media player | Windows, OS X, Linux, iOS, Android | Open-source media player. |
| Winamp | Windows, OS X, Android | Freeware media player. |
| Android, iOS | Internet radio player. | |
| Windows, Linux, OS X, Android | Open-source media player. | |
| Windows | Open-source media player |
Promotion aspects
Commercial trademarks and labeling
AAC-HE 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 AAC-HE v1 and eAAC+ to label support for AAC-HE v2 on their phones. Motorola uses AAC+ to indicate AAC-HE v1 and "AAC+ Enhanced" to indicate AAC-HE v2.Licensing and patents
Companies holding patents for AAC-HE have formed a patent pool administered by Via Licensing Corporation 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 AAC-HE encoders and/or decoders. Unlike the MP3 format before April 23, 2017, content owners are not required to pay license fees to distribute content in AAC-HE.
Standards
AAC-HE profile was first standardized in ISO/IEC 14496-3:2001/Amd 1:2003. AAC-HE v2 profile was first specified in ISO/IEC 14496-3:2005/Amd 2:2006. The Parametric Stereo coding tool used by AAC-HE v2 was standardized in 2004 and published as ISO/IEC 14496-3:2001/Amd 2:2004.The current version of the MPEG-4 Audio 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, Multimedia Messaging Service, Multimedia Broadcast/Multicast Service and Transparent end-to-end Packet-switched Streaming Service. AAC-HE version 2 was standardized under the name Enhanced aacPlus by 3GPP for 3G UMTS multimedia services in September 2004.
AAC-HE and AAC-HE v2 audio coding for DVB applications is standardized by TS 101 154. AacPlus v2 by Coding Technologies is also standardized by the ETSI as TS 102 005 for Satellite services to Handheld devices 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 and video H.264 with audio AAC-HEv2 in the 1Seg mobile sub-program.
Versions
The following is the summary of the different versions of AAC-HE:| Version | Common trade names | Codec feature | Standards |
| AAC-HE v1 | aacPlus v1, eAAC, AAC+, CT-aacPlus | AAC-LC + SBR | ISO/IEC 14496-3:2001/Amd 1:2003 |
| AAC-HE v2 | aacPlus v2, eAAC+, AAC++, Enhanced AAC+ | AAC-LC + SBR + PS | ISO/IEC 14496-3:2005/Amd 2:2006 |
| xAAC-HE | aacPlus v2, eAAC+, AAC++, Enhanced AAC+ | AAC-LC + SBR + PS + USAC | ISO/IEC 23003-3:2012/Amd 2:2012 |