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We were triggered by a user report that first looked like a severe crash. Lots of subtitle lines had got negative or huge durations. Not cool. Fortunately the user contacted us with a Screen Shot (thank you, Gustav) so we could try to find out what happened. It's about setting sync point toooooo close to each other. Let's explain what really happens while resyncing subtitles:

Usually you'd set 2 sync points. The difference between the original start times and new sync times are used to recalculate all the times between those 2 sync points. And then the magic starts ! ... This recalculation is extended to the front BEFORE the first sync point and to the back AFTER the second. That is because ALL the lines need to be resynced and the sync points act only as a reference.

So now take the following example: take 2 sync points in a subtitle file of 1000 lines just 5 lines apart ...

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... accept that you could "fix" a timing with a 150 millisecond accuracy (i don't think you can do that but well, let's assume you can :) ) .. if you now press the resync button, you could end up with subtitle lines with an error of 5 minutes !!! (150 milliseconds * 2 * 1000 = 300.000 milliseconds is 5 minutes) ... Now, to make it worse, if you would take 2 sync points in 2 consecutive lines and press the button, the recalculation will probably completely explode with unexpected results.

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99% of the subtitles are just a bit stretched or shrunken. Very often the shrink is only towards the end so why set sync points in the beginning of the file? They are already in place, not? Yes, they are. But you need to keep them there and protect there timings.

So just remember the golden rule if you have to do a simple resync: set one sync point somewhere at the beginning and one somewhere at the end. Even if the line is already in sync. That just makes it easier !!! :)))