How do you deal with videos that have no subtitles?

This has been bothering me for years. My media library contains a lot of content without subtitles: Somewhat obscure foreign-language films that can't be found on major subtitle sites (either they aren't listed on OpenSubtitles, or the available .srt files have mismatched timing, making manual adjustment a huge hassle). University lectures and conference presentations—content that generally no one bothers to subtitle. Various "long-tail" files: old documentaries, short videos with visuals, and so on. Things