Audio Lossless Coding

MPEG-4 Audio Lossless Coding, also known as MPEG -4 is to provide an extension to the MPEG-4 audio standard for lossless compression. The development of this extension was completed in December 2005.

Features

The method provides in comparing mediocre pack rates and decodes very quickly. Therefore it is

  • Probably very flexible, which affects different usage requirements ( slower / faster encoding / decoding - greater / less high packing rate )
  • Disclosed in contrast to the previous LPAC and described - as an open standard.

It supports

  • Samples to 32 bit - and floating point
  • Any sampling
  • Multi-channel capability (theoretically up to 216 = 65536 channels)
  • Tagging
  • Rapid light to any position in a file ( "Random Access " )
  • Streaming

By embedding in the MP4 container further features arise:

  • Tagging ( embedding additional information about the title, author, etc.)
  • Streaming capability
  • Error correction mechanisms
  • ( ReplayGain? )
  • Possibility of multiplexing with video material

On the subject of Practical additional options:

  • Optional separately storing the prediction signal and an error correction file are not of the world (or thoughts), the developer
  • Self-extracting files (see WavPack ) are not planned

History

In a call to the Moving Picture Experts Group in July 2002 for submission of lossless audio coding were seven letters in the given deadline until December. By March 2003, the compression efficiency, complexity and flexibility were evaluated. The choice then fell on the Lossless Predictive Audio Compression ( LPAC ) by Tilman Liebchen from the Communication Systems of the Technical University of Berlin, the successor of its Lossless Transform Audio Compression ( LTAC ). It was the method with the best packing rates among the candidates of the seven submitters and required little decoding complexity. In July 2003, it was officially declared a design for the future standard. The development of LPAC was set in late 2004/early 2005. The reference model LPAC was further developed with the participation of the Technical University of Berlin, RealNetworks and Nippon Telegraph and Telephone and supplemented by previously missing important features. As an ISO / IEC 14496-3:2001 / AMD 4, Audio Lossless Coding ( ALS) is the new standard will be introduced in 2005.

Technology

The input signal is decorrelated by an adaptive linear prediction filter and the residual signal entropy below with different Rice code. To determine the coefficients of the prediction filter the Levinson -Durbin algorithm is used.

Audioformat
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