Those files really contain 2 standard VP6 video streams:
 - the "normal" video stream
 - the alpha plan video stream (which is a standard
   YV12 video with it's U an V plans all set to 0)


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@10527 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b