title: FFMpeg creates MP4 which no browser can decode, but it can be played in VLC
body: <p>How can I debug what happened? I've tried this with variations to generate a short video from a single image:</p>
  
  <pre><code>ffmpeg -loop 1 -i black.png -vcodec libx264 -b 1500k -s 640x360 -t 1 out.mp4
  </code></pre>
  
  <p>tried:</p>
  
  <ol>
  <li>Changing aspect ration (or omitting it).</li>
  <li>using <code>-image2</code> instead of <code>-loop</code>.</li>
  <li>omitting bitrate.</li>
  <li>creating longer videos.</li>
  <li>also tried different syntax for specifying video codec: <code>-v:c libx264</code>.</li>
  <li>tried mpeg instead of libx264.</li>
  </ol>
  
  <p>In every case the effect is the same. The video plays in VLC, but not in the browser.</p>