LAPSE
A subtitle sync engine. It listens to the audio of a film, works out where people are talking and moves the subtitle to match. It fixes subtitles that start too late, drift further out over the runtime, or were made for a different cut of the film. Runs from the command line, as a Docker container that keeps a whole library in sync, or in the browser. Beats alass and ffsubsync in the benchmarks
LAPSE for Jellyfin
A plugin that puts LAPSE inside Jellyfin. Any film or episode gets menu entries to sync, shift, convert or extract its subtitles, and libraries can be set up to sync new items on their own.