Sample use case :
Below is a possible use case, when subtitles are late when compared to the audio.
Step 1 : Detect (“hear and see”) that subtitles are out of sync
(No high tech voice recognition needed here, just let the user detect it)
Step 2 : Press “Ctrl H” when you recognize a sentence you hear on the audio
Step 3 : Press “Ctrl J” when you read the same sentence in the subtitle
Step 4 : Press “Ctrl K” to correct the sync
Technical details
Shortcuts
The proposed workflow uses 3 shortcuts (^H, ^J, ^K) that are inspired by the already existing “J” and “H” shortcuts for subtitles synchronization
Subtitles delay
The result delay would applied as when entering the delay into the “Track synchronization” window (except that this way of calculating it requires much less brain cycles)
Note: as of now, if you enter a delay of 30 seconds in that window, you need to actually wait 30 seconds for the sync to be performed! Could that be improved?
What to do when subtitles are in advance when compared to the audio?
The principle would be the same, except that you would use the shortcuts in the following order :
Step 1 : Press “Ctrl J” --> Save subtitle timestamp when you read and memorize a sentence
Step 2 : Press “Ctrl H” --> Save audio timestamp when you hear the same sentence
Step 3 : Press “Ctrl K” --> Apply the delay
What about subtitle speed adjustments?
This process does not give a solution here.
However, by using the described shortcuts periodically (say, every 5 minutes), it might even still be usable.
Perhaps you could help to fix/implement also other open issues in VLC. VLC really needs skilled C++ volunteer developers.