title: ffmpeg - convert image sequence to video with reversed order
body: <p>Looking at <a href="https://trac.ffmpeg.org/wiki/Create%20a%20video%20slideshow%20from%20images" rel="nofollow noreferrer">the docs</a>, it is not apparent to me whether ffmpeg would allow me to convert an image sequence to a video in reverse order, for example using this sequence:</p>
  
  <pre><code>frame-1000.jpg
  frame-999.jpg
  frame-998.jpg
  ...
  frame-1.jpg
  </code></pre>
  
  <p>Is it possible to give a "step direction" for the frame indices?</p>