Add fmt to the list of media formats contained in *avff.
If *avff is NULL the function allocates the filter formats struct
and puts its pointer in *avff.
@return a non negative value in case of success, or a negative
value corresponding to an AVERROR code in case of error
Add fmt to the list of media formats contained in *avff. If *avff is NULL the function allocates the filter formats struct and puts its pointer in *avff.
@return a non negative value in case of success, or a negative value corresponding to an AVERROR code in case of error