| Audio Lossless Coding | |
|---|---|
| Developed by | ISO |
| Initial release | March 2006; 19 years ago (2006-03) |
| Latest release | RM23 2009; 17 years ago (2009) |
| Type of format | Losslessaudio |
| Contained by | MP4 |
| Standard | ISO/IEC 14496-3 |
| Open format? | Yes |
| Free format? | No |
MPEG-4 Audio Lossless Coding, also known asMPEG-4 ALS, is an extension to theMPEG-4 Part 3 audio standard to allowlosslessaudio compression. The extension was finalized in December 2005 and published asISO/IEC 14496-3:2005/Amd 2:2006 in 2006.[1] The latest description of MPEG-4 ALS was published as subpart 11 of theMPEG-4 Audio standard (ISO/IEC 14496-3:2019) (5th edition) in December 2019.[2]
MPEG-4 ALS combines a short-term predictor and a long term predictor. The short-term predictor is similar toFLAC in its operation – it is a quantizedLPC predictor with a losslessly coded residual usingGolomb Rice Coding orBlock 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.
As of 2020[update], there has not been wide acceptance of this format, possibly due to the lack of encoders and decoders available.[8]
Areference implementation of MPEG-4 ALS encoder and decoder (mp4als – e.g. mp4alsRM23) 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.[7]
There is a MPEG-4 ALS Decoder plugin forWinamp player.[9]
On November 11, 2009, theFFmpegopen source project gained an MPEG-4 ALS decoder in its development version.[10] Only a subset of the format is currently supported.
In July 2002, theMoving 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 ofTechnische Universität Berlin (TUB),RealNetworks, andNippon Telegraph and Telephone (NTT).