Currently the reference encoder uses a fixed block size, optimized on the sample rate of the input. Future version may vary the block size depending on the characteristics of the signal.
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Blocked data is passed to the predictor stage one subblock (channel) at a time. Each subblock is independently coded into a subframe, and the subframes are concatenated into a frame. Because each channel is coded independently, it means that one channel of a stereo frame may be encoded as a constant subframe, and the other an LPC subframe. The FLAC format has reserved space for supporting mid-side coding of stereo data, but it is currently not defined or implemented in the reference codec.
Blocked data is passed to the predictor stage one subblock (channel) at a time. Each subblock is independently coded into a subframe, and the subframes are concatenated into a frame. Because each channel is coded separately, it means that one channel of a stereo frame may be encoded as a constant subframe, and the other an LPC subframe.
FLAC currently defines two similar methods for the coding of the error signal from the prediction stage. The error signal is coded using Rice codes in one of two ways: 1) the encoder estimates a single rice parameter based on the variance of the residual, and Rice codes the entire residual using this parameter; 2) the residual is partitioned into several equal-length regions of contiguous samples, and each region is coded with its own Rice parameter based on the region's mean. (Note that the first method is a special case of the second method with one partition, except the Rice parameter is based on the residual variance instead of the mean.)
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The FLAC format has reserved space for other coding methods. Some possiblities for volunteers would be to explore better context-modeling of the Rice parameter, generic Golomb coding (Rice codes are a subset of Golomb codes where the Rice parameter k is the Golomb parameter m = 2^k), and Huffman coding. See <AHREF="http://www.hpl.hp.com/techreports/98/HPL-98-193.html">LOCO-I</A> and <AHREF="http://www.cs.tut.fi/~albert/Dev/pucrunch/packing.html">pucrunch</A> for descriptions of several universal codes.
The FLAC format has reserved space for other coding methods. Some possiblities for volunteers would be to explore better context-modeling of the Rice parameter, or Huffman coding. See <AHREF="http://www.hpl.hp.com/techreports/98/HPL-98-193.html">LOCO-I</A> and <AHREF="http://www.cs.tut.fi/~albert/Dev/pucrunch/packing.html">pucrunch</A> for descriptions of several universal codes.
