Download a YouTube videos subtitle file and choose a specific subtitle file format using yt-dlp.
To list the available subtitles on a YouTube video with yt-dlp:
yt-dlp --list-subs VIDEOURL
If the video has subtitles it will print them out including their available formats:
Language Name Formats en English vtt, ttml, srv3, srv2, srv1, json3
Choosing the language and saving it as a subtitle format file:
yt-dlp --write-subs en --sub-format json3 VIDEOURL
Or as default will be a .vtt file
yt-dlp --write-subs en https://www.youtube.com/watch?v=HOBDzc1ME5M