MPEG-4 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 enable lossless compression . Development of this extension was completed in December 2005.

features

In comparisons, the method delivers mediocre packing rates and decodes very quickly. For this it is

  • probably very flexible with regard to different usage requirements (faster / slower coding / decoding - higher / less high packing rates)
  • as an open standard - in contrast to its predecessor LPAC, disclosed and described.

It supports

  • Samples up to 32 bits - also floating point
  • any sampling frequencies
  • Multi-channel capability (theoretically up to 2 16 = 65536 channels)
  • Tagging
  • Quick jump to any position in a file ("Random Access")
  • Streaming audio

Embedding in the MP4 container results in additional features:

  • Tagging (embedding of additional information on the title, author, etc.)
  • Error correction mechanisms
  • Possibility of multiplexing with video material

On the subject of practical additional options :

  • optional separate storage of the prediction signal and an error correction file are not out of the world (or rather the thoughts) of the developers
  • Self-extracting files (see WavPack ) are not planned

history

In response to a call by the Moving Picture Experts Group in July 2002 for the submission of lossless audio coding methods , seven responses were received within the deadline set by December. Up to March 2003, their compression efficiency, complexity and flexibility were examined. The choice then fell on the Lossless Predictive Audio Compression (LPAC) from Tilman Liebchen from the Department of Communications at the Technical University of Berlin , the successor to his Lossless Transform Audio Compression (LTAC). It was the procedure with the best packing rates among the applicants from the total of seven entrants and required little decoding effort. In July 2003 it was officially declared the draft of the future standard. The development of LPAC was stopped in late 2004 / early 2005. The reference model LPAC was further developed with the participation of the TU Berlin, Real Networks and Nippon Telegraph and Telephone and supplemented with important features that were previously missing. The new standard was to be introduced in 2005 as ISO / IEC 14496-3: 2001 / AMD 4, Audio Lossless Coding (ALS) .

technology

The input signal is decorrelated by an adaptable linear prediction filter and the residual signal is subsequently entropy-coded with various Rice codes . The Levinson-Durbin algorithm is used to determine the coefficients for the prediction filter.

See also

Web links