Feature: test first N minutes

[Arthaey]

I'm trying substudy out on another file, and this one has timing issues that I thought I had fixed, but apparently didn't. So that means I have to try fixing the timing again, then hope that this time I got it right, then wait for substudy to process the entire video again, then re-import into Anki, before I can check if it's okay.

I wish there was a "test" feature of substudy, so that I could check the first 2 or 5 minutes of the video for timing issues, before "committing" to processing the entire video.

[emk]

Yes, this is one flag that I'm OK with. :-)