Avutil.SubtitleReturn the default ASS header used for subtitle encoders that require one (e.g. subrip, webvtt, ass).
type rectangle = {pict : pict option;flags : subtitle_flag list;rect_type : subtitle_type;text : string;ass : string;}type content = {format : int;start_display_time : int;end_display_time : int;rectangles : rectangle list;pts : int64 option;}val get_pts : frame -> int64 option