ffmpeg -i subs.srt subs.ass
-vf ass=subtitles.ass
mencoder dvd://1 -sid 0 -oac copy -ovc copy -vobsubout subtitles -o bla
creates sub/idx files. Use online converter to convert to srt.
https://subtitletools.com/convert-sub-idx-to-srt-online
Synchronise srt files: