@param st stream that the timestamp belongs to
@param timestamp timestamp to retrieve the index for
@param flags if AVSEEK_FLAG_BACKWARD then the returned index will correspond
to the timestamp which is <= the requested one, if backward
is 0, then it will be >=
if AVSEEK_FLAG_ANY seek to any frame, only keyframes otherwise
@return < 0 if no such timestamp could be found
Get the index for a specific timestamp.
@param st stream that the timestamp belongs to @param timestamp timestamp to retrieve the index for @param flags if AVSEEK_FLAG_BACKWARD then the returned index will correspond to the timestamp which is <= the requested one, if backward is 0, then it will be >= if AVSEEK_FLAG_ANY seek to any frame, only keyframes otherwise @return < 0 if no such timestamp could be found