Subtitle Editor seems to be the go-to program for editing subtitles. However, being on a Mac, that’s no good for me as there are only Windows and Linux versions. The thing with having a Linux version of a tool though is that there’s a very good chance that it exists in Docker and that is, indeed, the case here.
https://hub.docker.com/r/fresta/subtitleedit
docker run --name=subtitleedit -e WIDTH=1280 -e HEIGHT=720 -p 3389:3389 -p 8080:8080 -v /media:/media fresta/subtitleedit
Just set /media to be something useful.