fourcc (LSB first, so "ABCD" -> ('D'<<24) + ('C'<<16) + ('B'<<8) + 'A'). this is used to workaround some encoder bugs
- encoding: set by user, if not then the default based on codec_id will be used
- decoding: set by user, will be converted to upper case by lavc during init
Definition at line 687 of file avcodec.h.