Explicitly set the number of bits per sample to stop
the avi muxer from guessing at 24 bits.
The result is that bits per pixel in the avi stream header
matches what other XSUB muxers produce, such as AVIAddXSubs.exe
Signed-off-by: Erik Olofsson <eaj.olofsson@gmail.com>
Reviewed-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>