title: Combining audio and video tracks into new MediaStream
body: <p>I need to get create a MediaStream using audio and video from different MediaStreams.  In Firefox, I can instantiate a new MediaStream from an Array of tracks:</p>
  
  <pre><code>  var outputTracks = [];
    outputTracks = outputTracks.concat(outputAudioStream.getTracks());
    outputTracks = outputTracks.concat(outputVideoStream.getTracks());
    outputMediaStream = new MediaStream(outputTracks);
  </code></pre>
  
  <p>Unfortunately, this doesn't work in Chrome:</p>
  
  <blockquote>
    <p>ReferenceError: MediaStream is not defined</p>
  </blockquote>
  
  <p>Is there an alternative method in Chrome for combining tracks from separate streams?</p>