title: FFMPEG: Extracting 20 images from a video of variable length
body: <p>I've browsed the internet for this very intensively, but I didn't find what I needed, only variations of it which are not quite the thing I want to use.</p>
  <p>I've got several videos in different lengths and I want to extract 20 images out of every video from start to the end, to show the broadest impression of the video.</p>
  <p>So one video is 16m 47s long =&gt; 1007s in total =&gt; I have to make one snapshot of the video every 50 seconds.</p>
  <p>So I figured using the -r switch of ffmpeg with the value of 0.019860973 (eq 20/1007) but ffmpeg tells me that the framerate is too small for it...</p>
  <p>The only way I figured out to do it would be to write a script which calls ffmpeg with a manipulated -ss switch and using -vframes 1 but this is quite slow and a little bit off for me since ffmpegs numerates the images itself...</p>