I wish VLC, plex, video players in general had the ability to automatically sync subs to audio. (automatically, not manually)
We have the technology; everything we need to do this exists. It's just not done automatically, and when using slightly off-sync subs, you have to fiddle with sub timing for ages until you find the right sync. Even more so when the subtitles have different off-sync issues for the whole movie/episode.
And you need to do the manual thing so rarely, that you always forget that does the delay need to be positive or negative if the subtitles are fast. =)
And then VLC does this weird freeze thing to catch up that can't be aborted, so if you accidentally type an extra zero into delay, good luck waiting for that to stop haha. Usually faster to just restart the damn thing.
Given our capabilities, it's really a straightforward thing to do. YouTube does it automatically (you drop in your script with the video, it auto-syncs everything).
It could even be done for when the language doesn't match, given an auto-translation pass and some heuristics.
I think this is what the OP refers to with "fiddle around for ages". I know the problem not with subs, but when audio is off related to the image. And of course the problem is rare enough that I am never "in training", and have to find a remarkable spot first (e.g. door slam shut or a suitable spot in dialogue), then think about going backwards or forwards, guess the amount, etc. etc. :)
If the whole subtitle file is out of sync (e.g. every line is late 2s), one shortcut is all it takes. In that 1/10 case, you do need to 'fiddle around for ages', but given that all other options (e.g. SubtitleEdit[1]) are way more complicated and time consuming, mpv is all I could suggest. For the problem with audio and image being out-of-sync, I have no idea :)
For AV sync you can do this in the receiver (and some devices with e.g. Bluetooth support for speakers) because it's not really a problem with the source material (typically anyway) it's just something that does need tuning to the room & hardware.
I use Bazarr to automate downloading of subtitles for my movies and TV shows, and it integrates subsync. Works 99% of the time, if it doesn't I find the subs for that particular series are consistently offsync by 1.0s which is easy to fix with decent media players.
We have the technology; everything we need to do this exists. It's just not done automatically, and when using slightly off-sync subs, you have to fiddle with sub timing for ages until you find the right sync. Even more so when the subtitles have different off-sync issues for the whole movie/episode.