I have been trying to fix this issue for weeks. I found videos and tutorials on how to add subtitles automatically via subtitles.org and that seems to work. My problem is that the timing of the subtitles are way off and in some cases more than 10-20 seconds off from the actual dialogue.
there’s usually quite a number of different versions of each movie “in the wild” – sometimes that’s actually different versions (theatrical, directors cut, extended edition…), sometimes it’s just due to the local distributors adding their own logo with a different runtime.
That’s why those subtitles might work flawlessly for users in certain countries and others have a constant fight with them. Plex itself provides no adjustment option for subtitles (which might help if it’s constantly a fixed amount of time off). You might try if your TV can add a time shift to the subtitles. Otherwise you’ll depend on searching for the “right” subtitles matching your video.
I usually just dump any Subs that are not properly timed via Sub-Sero, I ban the Sub, then I force-install a new Sub. It usually finds a proper sub when you force it. On one occasion, the replacement sub was also out of whack, so I had to ban that sub too.
What you have to watch out for are subs where the maker added all kinds of spam ASCII animation, with popup links and email addresses and phone numbers even. I don’t mind a sub maker putting their mark on a sub, but I won’t tolerate Spam.
Not really any way to adjust subs in Plex though, if a sub is out of sync, check it in MPC-HC (Not VLC). If it’s out of whack there, it’s out of whack, get a new Sub. (VLC sometimes allows the timing to drift).
Most movies have good Subs, sometimes a Fanedit won’t have many. But with Fanedits,. they are made for a specific Fanedit, so just look for the version of the Fanedit you have. Sometimes, a movie won’t have subs in your language at all.