mpeg4videoparse: Need detect picture coding type when drain
Submitted by kevin
Link to original bug (#749617)
Description
our use case is demuxer only output key frame when backward playback. every frame is DISCONT and KEY frame. mpeg4videoparse will detect coding type when detect start code after VOP. our use case will drain after VOP and can't detect start code after VOP. Add check coding type code when drain.