title: How can I generate a video file directly from an FFmpeg filter with no actual input file?
body: <p>FFmpeg has a number of video generating filters, listed in the documentation as "<a href="http://ffmpeg.org/ffmpeg-filters.html#Video-Sources">video sources</a>":</p>
  
  <ul>
  <li>cellauto</li>
  <li>color</li>
  <li>mptestsrc</li>
  <li>fei0r_src</li>
  <li>life</li>
  <li>nullsrc, rgbtestsrc, testsrc</li>
  </ul>
  
  <p>Those are great for using with other filters like overlay, but is there any way that I can generate a movie consisting of just one of those video sources without any input video?</p>
  
  <p>Something like:</p>
  
  <pre><code>ffmpeg -vf color=red" red_movie.mp4
  </code></pre>
  
  <p>Except that that errors out with <strong><code>At least one input file must be specified</code></strong>.</p>