Audio Lossless Coding

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MPEG-4 Audio Lossless Coding, also known as MPEG-4 ALS, is an extension to the MPEG-4 audio standard to allow lossless audio compression. The extension was finalised in December 2005.

MPEG-4 ALS is similar to FLAC in its operation. Simply put it is a quantized LPC predictor with a losslessly coded residual using Golomb Rice Coding or Bounded Gilbert Moore Coding (BGMC).

Features inlude:

Support for PCM resolutions of up to 32-bit
Arbitrary sampling rates
Multi-channel / multi-track support (up to 65536 channels)
Fast random access to any part of the encoded data.
Tagging
Streaming
Error correction mechanisms
Can be multiplexed with video data

As of 2006, there has not been wide acceptance of this format, possibly due to the lack of encoders and decoders available. A reference encoder and decoder can be obtained at the MPEG-4 ALS homepage.

[edit] 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 NTT.