Merges two ASS subtitle files with different languages into a combined ASS file so you can have 2 sets of subtitles on your film at once.
One language is displayed at the bottom and one on the top as defined by the Alignment style in the ASS file.
sudo npm i -g multi-language-ass
multiass subs-en.ass subs-vi.ass > subs-combined.ass
TODO: integrate a converter so this happens automatically for input files.
However for now an easy way to convert is with ffmpeg. For example:
ffmpeg -i film_en.srt film_jp.ass