Hello,
Sorry for digging up such an old thread but I think this is worth it.
The feature mentioned above is really useful for anyone dealing with subtitles at all, especially nowadays, when the availability of these is overwhelming and it is no longer a luxury to have subtitles for every movie in the collection. Usually, while searching for subtitles there are tens of those for just one movie and the only difference between them is the timing/sync. The text is usually ok in all of them, so this feature would save a lot of time because if the subtitles aren't synced correctly, the user can 'correct' this by a single keypress saying that *NOW* is the right time to show the next (previous) line of text. The player then shifts all the subtitles and this usually corrects the sync for at least a few minutes, or in case fps is correct it may even fix sync for the whole movie.
To sum this up: instead of syncing via special tools (overwhelming) or constantly pressing +/-, a few keypresses would usually fix the subtitles.
It is there in mplayer/mpv (and by proxy in SMPlayer) since years (AFAIR assigned to keys G and Y by default), so if anyone has any doubts about its usefulness, one can try this feature in there.
Now, pretty please, someone implement this in Kodi!
... or am I missing something? I could only find this thread and nothing else.