contribution by Laszlo Torok <torokl@alpha.dfmk.hu>
4CC 'MAC3' and 'MAC6' in Quicktime.
It works for mono streams, needs to be fixed for stereo when I get my hands on a stereo sample :)
patch by (François Revol <revol at free dot fr>)
Originally committed as revision 1145 to svn://svn.ffmpeg.org/ffmpeg/trunk
François Revol