audio/alac - The NetBSD Packages Collection

Located here is a basic decoder for Apple Lossless Audio Codec files
(ALAC). ALAC is a proprietary lossless audio compression scheme. Apple
never released any documents on the format.
What I provide here is a C implementation of a decoder, written from
reverse engineering the file format. It turns out that most of the
algorithms in the codec are fairly well known. ALAC uses an adaptive FIR
prediction algorithm and stores the error values using a modified rice
or golumb algorithm. Further details are in alac.c.

Although an encoder is not provided, by using the decoder as a sort of
specification it should be fairly trivial to write an encoder. By
exploiting other lossless audio encoders, such as FLAC, the task will be
much easier. Although one wouldn't be able to copy the compression
algorithms verbatim, as adaptive compression is used in ALAC and not in
FLAC. There are, however, a bunch of academic papers on the issue.

The program located here will not be able to handle all ALAC files, it
can only handle mono or stereo files. ALAC allows up to 8 channels. It
should be trivial to finish the implementation once I find files that I
can test it with. The ALAC decoder supports both 16 and 24 bit sample
sizes.