If you’re in the habit of downloading your movies and subtitles separately, you’ve probably experienced some awkward lags between the subtitles and the audio track.
With VLC it’s easy to readjust the audio/video/subtitle timing, but if you want to automate the process you would need something like SubSync .
SubSync works roughly like this: It divides the video and the subtitles in small pieces of 10ms and for each division, determines if dialogue is present (audio).
It then proceeds to realign the subtitles timecodes with these moments of dialogue.
You can install this tool as follows: