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Audio Lossless Coding

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

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]

MPEG-4 ALS 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]

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)[4]
  • Multi-channel / multi-track support (up to 65536 channels)
  • Fast random access to any part of the encoded data.
  • Tagging
  • Streaming[4]
  • Error correction mechanisms[5]
  • 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" is currently under development (as of 2009).[6]

Software support

As of 2006, there has not been wide acceptance of this format, possibly due to the lack of encoders and decoders available.[5]

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.[7]

On November 11, 2009, the FFmpeg open source project gained an MPEG-4 ALS decoder in its development version.[8]

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 declared as the official 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. ^ a b c d Communication Systems Group (2009-10-01). "MPEG-4 Audio Lossless Coding (ALS)". Technische Universität Berlin. Retrieved 2009-10-08.
  3. ^ Tilman Liebchen: Technical Universifty 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 Universifty of Berlin. Retrieved 2009-10-08.{{cite web}}: CS1 maint: multiple names: authors list (link)
  4. ^ a b Noboru Harada, Takehiro Moriya, and Yutaka Kamamoto (2009-05-07). "MPEG-4 ALS: Performance, Applications, and Related Standardization Activities". NTT Technical Review. Retrieved 2009-10-08.{{cite web}}: CS1 maint: multiple names: authors list (link)
  5. ^ a b Hydrogenaudio Knowledgebase (2006). "Lossless comparison - Comparison Table". Hydrogenaudio Knowledgebase. Retrieved 2009-10-08.
  6. ^ ISO/IEC JTC1/SC29/WG11 (2009-07-03), ISO/IEC 14496-3:200X/PDAM 2 – ALS Simple Profile and Transport of SAOC - N10826 (DOC), retrieved 2009-10-15{{citation}}: CS1 maint: numeric names: authors list (link)
  7. ^ "MPEG-4 ALS Decoder plugin 1.00 for Winamp". Codecs.com. 2007-06-05. Retrieved 2009-10-08.
  8. ^ FFmpeg (2009-11-11). "FFmpeg-cvslog r20517". FFmpeg. Retrieved 2009-11-20.
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