title: MediaRecorder : videos saved on chrome do not show on firefox
body: <p>I do use mediaRecorder:</p>
  
  <p>when I record on FF: FF and chrome: ok</p>
  
  <p>when I record on chrome: chrome is ok and firefox returns: unknown MimeType</p>
  
  <p>When I do examine these recorded videos: I got for chrome: </p>
  
  <blockquote>
  <pre><code>Stream #0:1(eng): Video: h264 (Constrained Baseline), yuv420p(progressive), 640x480, SAR 1:1 DAR 4:3, 1k tbr, 1k tbn, 2k tbc
  </code></pre>
    
    <p>(default)</p>
  </blockquote>
  
  <p>and for firefox: </p>
  
  <blockquote>
    <p>Stream #0:0(eng): Video: vp8, yuv420p(progressive), 640x480, SAR 1:1
    DAR 4:3, 1k tbr, 1k tbn, 1k tbc (default</p>
  </blockquote>
  
  <p>in JS I do use: </p>
  
  <pre><code>var options = {mimeType: 'video/webm;codecs=vp8'};
  </code></pre>
  
  <p>Any idea on how to record videos on chrome so firefox can read them ?</p>