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MPEG-4 Audio Lossless Coding

An extension to the MPEG-4 Part 3 audio standard to allow lossless audio compression.

MPEG-4 Audio Lossless Coding, also known as MPEG-4 ALS, is an extension to the MPEG-4 Part 3 audio standard to allow lossless audio compression. The extension was finalized in December 2005 and published as ISO/IEC 14496-3:2005/Amd 2:2006 in 2006. The latest description of MPEG-4 ALS was published as subpart 11 of the MPEG-4 Audio standard (ISO/IEC 14496-3:2009) (4th edition) in August 2009.

MPEG-4 ALS combines together a short-term predictor and a long term predictor. The short-term predictor is similar to FLAC in its operation - it is a quantized LPC predictor with a losslessly coded residual using Golomb Rice Coding or Block Gilbert Moore Coding (BGMC). The long term predictor is modeled by 5 long-term weighted residues, each with its own lag (delay). The lag can be hundreds of samples. This predictor improves the compression for sounds with rich harmonics (containing multiples of a single fundamental frequency, locked in phase) present in many musical instruments and the human voice.

  • Support for PCM resolutions of up to 32-bit
  • Arbitrary sampling rates (tested up to 192 kHz, higher frequencies such as 384 kHz can be handled with the current specifications)
  • Multi-channel / multi-track support (up to 65536 channels)
  • Fast random access to any part of the encoded data.
  • Tagging
  • Streaming
  • Error correction mechanisms
  • Optional storage in MP4 file format
  • Can be multiplexed with video data using MP4 file format
  • An MPEG-4 Audio profile "ALS Simple Profile".

Key Terms

als
audio lossless coding
audio standard
extension
iso iec
lag
long term predictor
lossless audio compression
part
short term predictor

Additional Resources

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Acronymn

MPEG-4 ALS

Synonymns

MPEG-4 Audio Lossless Coding
Audio Lossless Coding

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Sources & Credits

Last modified on May 25 2020
Content adapted from Wikipedia
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