title: ffmpeg - how to make a preview with short bursts of scenes
body: <p>Given a list of timestamps, how can I make a movie where I will extract x seconds at each of the timestamps?</p>
  
  <p>for example, if my list is [3, 8, 11], I would like to make a movie made of [3-4][8-9][11-12]</p>
  
  <p>I know how to extract the frames at the timestamps, but not how to extract a chunk of the movie from a list.</p>