/**
* fourcc (LSB first, so "ABCD" -> ('D'<<24) + ('C'<<16) + ('B'<<8) + 'A').
* this is used to workaround some encoder bugs
+ * a demuxer should set this to what is stored in the field used to identify the codec
+ * if there are mutiple such fields in a container then the demuxer should choose the one
+ * which maximizes the information about the used codec
+ * if the codec tag field in a container is larger then 32bit then the demxuer should
+ * remap the longer id to 32bit with a table or other structure alternatively a new
+ * extra_codec_tag + size could be added but for this a clear advantage must be demonstrated
+ * first
* - 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
*/