rockbox/apps/codecs/libcook/README.rockbox

Library: libcook
Imported by : Mohamed Tarek

These files comprise a rm parser and a cook decoder based on the decoder
from ffmpeg.

LICENSING INFORMATION

ffmpeg is licensed under the Lesser GNU General Public License and the
file cook.c is Copyright 2003 Sascha Sommer and 2005 Benjamin Larsson.

IMPORT DETAILS

The decoder is based on ffmpeg-svn r18079.

The file libavcodec/cook.c was modified to remove all ffmpeg-specific
code and to use the current rm parser.

In initializing random_state in COOKContext, ffmpeg used a random_seed()
function that was weird in the way it gets the random number. So it was
decided to not use this function at all,and the value was initialized to 1,
because according to Benjamin Larsson random_seed() could just be 
replaced by any value.

The current files contain lots of code which is either not needed by
the decoder or totally disabled (#if 0 .. #endif) to enable
compiling. This was during the isolation of the decoder from ffmpeg,
the intention was to take as few files as possible to be able to
compile cook.c and the related files outside ffmpeg.

The decoder still uses floating point and relies on dynamic allocations 
in some parts of it. It's still not ready to be ported to rockbox.

CONVERSION TO FIXED-POINT

A patch from ffmpeg's mailing list was used to convert the decoder to
use fixed-point arithmetic. The patch was done by Ian Braithwaite, and
discussed here :

http://thread.gmane.org/gmane.comp.video.ffmpeg.devel/46024

The patch is a bit dated (2007) so the modifications to cook.c had to
be done manually.  The patch was also applied to cookdata.h and was
used to create cookdata_fixpoint.h, cook_fixpoint.h and
cook_fixp_mdct.h.

The patch used a cook_random() function for noise filling. this was
dropped and av_lfg_get() was used instead for consistency.

Note : Only parts of the patch were committed to ffmpeg's repository.

TESTING

The test program should compile in any Unix-like environment using the
command "make -f Makefile.test".

Running "./cooktest file.rm" will decode the audio data to a WAV file
called "output.wav" in the current directory.