Advanced Audio Coding

• FourCC: AAC AACP MP4A mp4a VLB
• Company: ISO
• Samples: http://samples.mplayerhq.hu/A-codecs/AAC/
• Samples: sample repo at standards.iso.org
• Sample Docs: sample docs

Specification and reference source links.

• http://www.3gpp.org/ftp/specs/html-info/26-series.htm
• ftp://ftp.tnt.uni-hannover.de/pub/MPEG/audio/mpeg4/
• AAC Reference Software

Google has opensourced Android, which includes an Apache 2.0 licensed aac decoder:

• http://git.source.android.com/?p=platform/external/opencore.git;a=tree;f=codecs_v2/audio/aac/dec;hb=HEAD

Intel has source for its IPP based AAC decoder:

• http://www.intel.com/cd/software/products/asmo-na/eng/perflib/ipp/219611.htm?prn=y

Real Networks has source for its Helix AAC fixedpoint decoder here:

• https://datatype.helixcommunity.org/2005/aacfixptdec

Usually stored in an MP4 container.

See also Understanding AAC.

Extensions

HE-AAC

HE-AAC (also known as by the Dolby trade name aacPlus) is AAC-LC + SBR (Spectral Band Replication) and HE-AAC v2 (aacPlus v2) is LC-AAC + 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
  • MP3PRO that also uses SBR.
  • 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. DivX Inc. is one company that uses MPEG Surround technology to achieve 5.1 channel surround sound in smaller files.

GAIN headers

See http://mp3gain.sourceforge.net and MP3 GAIN header.