[IanCal]

It's tricky. Subs aren't always brilliantly timed either.

I did something similar many moons ago to auto create summary videos based on changing sentiment in the subtitles for the BBC. Worked... interestingly.

If you want to nail scene changes, one thing you can do is look for sudden changes to the histogram frame by frame. It'll change pretty smoothly as people move, cameras move etc but there's a discontinuity when there's a cut. One issue though then is that there are a lot of camera cuts! Surprising how many there are that you don't really notice.