[FFmpeg-devel] [PATCH] add fixed coeff LPC mode to alac encoder

[Justin Ruggles]

Hi,

We currently do not have a regression test for the ALAC encoder like we
do for FLAC.  The ALAC encoder has 2 compression levels, one
uncompressed, which does not cover much of the code, and one which uses
floating point when calculating LPC coefficients, which does not lend
itself to reliable regression tests across all test platforms.

The way we do regression testing with FLAC is to use the fixed LPC
coefficient mode, which skips the floating-point parts but still covers
prediction, entropy coding, and other parts in the regression test.

Here is a patch to the ALAC encoder to add a fixed-coeff LPC mode using
compression_level == 1.  This will allow us to add a round-trip
encode/decode regression test.  The default compression level is changed
to 2 and keeps the same behavior.  The fixed-coeff mode is about 20%
faster but has about 6% worse compression (about the same as FLAC with
compression level 2).

Thanks,
Justin

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