Advanced Audio Coding

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Specification links:

Reference Sources:

Usually stored in an MP4 container.

See also Understanding AAC.


With Source Code

Other Notables

Common AAC Flavors


The basic subset of AAC that most other flavors and profiles are based on.

The AAC Profile (MPEG-4 AAC-LC)

MPEG-2 AAC-LC plus a Perceptual Noise Substitution (PNS) tool.

The HE-AAC Profile (v1 and v2)

HE-AAC (also known as by the Dolby trade name aacPlus) is MPEG-4 AAC-LC + SBR (Spectral Band Replication) and HE-AAC v2 (aacPlus v2) is MPEG-4 AAC-LC + SBR + PS (Parametric Stereo). Standard AAC-LC decoders can decode HE-AAC encoded files/streams but without SBR and PS you do not get the full quality.

  • See also

MPEG-2/4 AAC Main

MPEG-2/4 AAC-LC plus a computationally intensive, intra-channel, inter-frame frequency domain prediction tool. Additionally this profile adds relaxation to the maximum TNS filter size, and time domain coupling. The details of the prediction tool are only given in ISO/IEC 13818-7 not in ISO/IEC 14496-4. This flavor is rarely seen in the wild.


MPEG-4 AAC-LC plus a less computationally intensive frequency domain prediction tool. This flavor is rarely seen in the wild. Despite being an MPEG-4 only flavor it can be embedded in an ADTS stream.


Bit Slice Arithmetic Coding (BSAC) is an alternate quantization and entropy coding scheme for AAC. It is used by the T-DMB broadcast standard.


GAIN headers

See and MP3 GAIN header.

MPEG Surround

MPEG Surround that can used for all audio but especially MP3/mp3PRO and AAC/aacPlus. MPEG Surround technology share similar characteristics with SBR (Spectral Band Replication) and PS (Parametric Stereo), which MP3PRO and AAC+ decoders also use.

AAC Encoding Guidelines

The following documents are must reads for anyone implementing an AAC encoder

  • ISO/IEC 14496-3:2009 - Decoding AAC, systems MPEG-4 integration
  • ISO/IEC 14496-4:2004 (14496-26:2009) - Conformance, includes limits on various bitstream values
  • ISO/IEC 14496-24:2008 - ISO Gapless AAC
  • ISO/IEC 13818-7:2006 - MPEG-2 AAC includes informative annexes on encoding omitted from 14496-3
  • 3GPP 26.403-405 - Elaborations on the annexes in 13818-7
  • Improved ISO AAC Coder, Ivan Dimkovic, PsyTEL Research