+1, It should be a per-video setting that will save so that when watching the video again or watch a different video you will not have to re-adjust the subtitle delay.
This would indeed be good. Is it possible to have a button to allow server side override for viewers? So that when they adjust the subtitle (or download a new one) to fit the movie on emby, it saves to the server so any other account that watches the movie gets improved subtitles instead of the out of sync ones? Would be nice, but I guess it should be optional since some server administrators might not want their viewers to mess with their subtitles (specially those that have done them all manually themselves)?