Hierarchical structure of AAC profile, AAC-HE profile and AAC-HE v2 profile, and compatibility between them. The AAC-HE profile decoder is fully capable of decoding any AAC profile stream. Similarly, The AAC-HE v2 decoder can handle all AAC-HE profile streams as well as all AAC profile streams. Based on the MPEG-4 Part 3 technical specification.
Evolution from MPEG-2 AAC-LC (Low Complexity) Profile and MPEG-4 AAC-LC Object Type to AAC-HE v2 Profile.
The progenitor of AAC-HE 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 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.
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 (e.g., 24 kbit/s).
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.
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.
Die Plattenkiste 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.
XLD, 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.
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 released Dolby Pulse decoders and encoders in September 2008. AAC-HE v2 is the core of Dolby Pulse so files and streams encoded in Dolby Pulse will playback on AAC, AAC-HE v1 and v2 decoders. Conversely files and streams encoded in AAC, AAC-HE v1 or v2 will playback on Dolby Pulse decoders.
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
Dolby has additionally released a PC decoder as an SDK suitable for integration into PC applications requiring Dolby Pulse, AAC-HE or AAC playback capabilities.
AAC-HE v2 decoders are provided in all versions of Android. Decoding is handled by Fraunhofer FDK AAC since Android version 4.1.
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.
AAC-HE profile was first standardized in ISO/IEC 14496-3:2001/Amd 1:2003. AAC-HE v2 profile (AAC-HE with Parametric Stereo) 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 (including AAC-HE standards) is published in ISO/IEC 14496-3:2009.
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 (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 AAC-HEv2 in the 1Seg mobile sub-program.
The following is the summary of the different versions of AAC-HE:
^To deliver streaming audio, AAC data is most likely carried in either the Audio Data Interchange Format (ADIF) or via Audio Data Transport Stream (ADTS). You can parse these containers and create FLV audio tags in order to use the audio file with Data Generation Mode.