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. The latest description of MPEG-4 ALS was published as subpart 11 of the MPEG-4 Audio standard 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. The long term predictor is modeled by 5 long-term weighted residues, each with its own lag. The lag can be hundreds of samples. This predictor improves the compression for sounds with rich harmonics present in many musical instruments and human voice.

Features

, there has not been wide acceptance of this format, possibly due to the lack of encoders and decoders available.
A reference implementation of MPEG-4 ALS encoder and decoder 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.
There is a MPEG-4 ALS Decoder plugin for Winamp player.
On November 11, 2009, the FFmpeg open source project gained an MPEG-4 ALS decoder in its development version.

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 was selected as the first draft for the future standard. The reference model was further developed under participation of the Technical University of Berlin, RealNetworks, and Nippon Telegraph and Telephone.