Audio Lossless Coding

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.[1] 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.[2]

Audio Lossless Coding
Developed byISO
Type of formatAudio compression format
Contained byMP4
StandardISO/IEC 14496-3

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).[3][4] 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 human voice.

Features
  • Support for PCM resolutions of up to 32-bit [2]
  • Arbitrary sampling rates (tested up to 192 kHz, higher frequencies such as 384 kHz can be handled with the current specifications)[5]
  • Multi-channel / multi-track support (up to 65536 channels)
  • Fast random access to any part of the encoded data.
  • Tagging
  • Streaming[5]
  • Error correction mechanisms[6]
  • Optional storage in MP4 file format[2]
  • Can be multiplexed with video data using MP4 file format
  • An MPEG-4 Audio profile "ALS Simple Profile".[7]

Software support

As of 2020, there has not been wide acceptance of this format, possibly due to the lack of encoders and decoders available.[6]

A reference implementation of MPEG-4 ALS encoder and decoder (mp4als - e.g. mp4alsRM22rev2) can be obtained at the MPEG-4 ALS homepage and it was also published as ISO/IEC 14496-5:2001/Amd 10:2007/Cor 3:2009.[2]

There is a MPEG-4 ALS Decoder plugin for Winamp player.[8]

On November 11, 2009, the FFmpeg open source project gained an MPEG-4 ALS decoder in its development version.[9]

History

In July 2002, the Moving Picture Experts Group issued a call for proposals of lossless audio coding procedures to be sent in before December. Seven companies submitted their proposals which were examined taking into consideration compression efficiency, complexity and flexibility. By July 2003, Lossless Predictive Audio Compression (LPAC) was selected as the first draft for the future standard. The reference model was further developed under participation of the Technical University of Berlin (TUB), RealNetworks, and Nippon Telegraph and Telephone (NTT).

See also

References
  1. ISO (2006). "Audio Lossless Coding (ALS), new audio profiles and BSAC extensions - ISO/IEC 14496-3:2005/Amd 2:2006". ISO. Retrieved 2009-10-07.
  2. Communication Systems Group (2009-10-01). "MPEG-4 Audio Lossless Coding (ALS)". Technische Universität Berlin. Retrieved 2019-03-21.
  3. Tilman Liebchen & Yuriy Reznik (2004-04-03). "MPEG-4 ALS: an Emerging Standard for Lossless Audio Coding" (PDF). Data Compression Conference. Retrieved 2010-09-03.
  4. Tilman Liebchen: Technical University of Berlin, T. Moriya, N. Harada, Y. Kamamoto: NTT Communication Science Labs; Y. Reznik: RealNetworks Inc. (2005-08-03). "The MPEG-4 Audio Lossless Coding (ALS) Standard - Technology and Applications" (PDF). Technical University of Berlin. Retrieved 2009-10-08.CS1 maint: uses authors parameter (link)
  5. Noboru Harada; Takehiro Moriya & Yutaka Kamamoto (2009-05-07). "MPEG-4 ALS: Performance, Applications, and Related Standardization Activities". NTT Technical Review. Retrieved 2009-10-08.
  6. Hydrogenaudio Knowledgebase (2006). "Lossless comparison - Comparison Table". Hydrogenaudio Knowledgebase. Retrieved 2009-10-08.
  7. ISO/IEC JTC1/SC29/WG11 (2009-07-03), ISO/IEC 14496-3:200X/PDAM 2 – ALS Simple Profile and Transport of SAOC - N10826, archived from the original (DOC) on 2014-07-29, retrieved 2009-10-15CS1 maint: uses authors parameter (link)
  8. "MPEG-4 ALS Decoder plugin 1.00 for Winamp". Codecs.com. 2007-06-05. Retrieved 2009-10-08.
  9. FFmpeg (2009-11-11). "FFmpeg-cvslog r20517". FFmpeg. Archived from the original on 2010-02-11. Retrieved 2009-11-20.
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