Some online video players give you the option to add or subtract delay e.g. by ±0.5s to subtitles to manually sync them to the video currently playing. However I become functionally dyslexic when it comes to actually figuring out how much delay has to be added. I end up randomly adding or subtracting delay and make it work through trial and error.
Is there some rule of thumb I could follow instead to systematically sync subtitles?
I don’t know what software you are using and if they are indicating the direction of error or correction, but I trust if you try it you’ll figure it out.
Put on media with properly synchronized subtitles. Change to plus five. Are the subs behind or ahead of audio? Make a note. Now you know.