title: pipe ffmpeg output for video preview
body: <p>I want to pipe <code>ffmpeg</code> output to be able to get it as a stream. More precisely, I have a video that is remotely hosted and I want to compute a preview and save it directly to S3.</p>
  
  <pre><code>ffmpeg -i http://mywebsite.com/video.mp4 -ss 00:00:01 -vframes 1 -f image2 ~/test.jpg
  </code></pre>
  
  <p>works (no streaming here) but this doesn't:</p>
  
  <pre><code>ffmpeg -i http://mywebsite.com/video.mp4 -ss 00:00:01 -vframes 1 -f image2 pipe:1 | echo &gt; ~/Downloads/test.image2
  </code></pre>
  
  <p>The latest will create a 1 byte file that is obviously not the desired output. I don't know what format <code>image2</code> is but I had to specified an output format for the streaming command to run. It works fine without streaming.</p>
  
  <p>Any clue?</p>