Draw ASS (Advanced Substation Alpha) subtitles on top of input video using the libass library.

To enable compilation of this filter you need to configure FFmpeg with --enable-libass.

This filter accepts the syntax: ass_filename[:options], where ass_filename is the filename of the ASS file to read, and options is an optional sequence of key=value pairs, separated by ":".

A description of the accepted options follows.

original_size

Specifies the size of the original video, the video for which the ASS file was composed. Due to a misdesign in ASS aspect ratio arithmetic, this is necessary to correctly scale the fonts if the aspect ratio has been changed.

For example, to render the file sub.ass on top of the input video, use the command:

ass=sub.ass