title: Why does mediaDevices.enumerateDevices list some devices twice? What is default?
body: <p>I write this code in JavaScript in Chrome:</p>
  
  <pre><code>navigator.mediaDevices.enumerateDevices()
    .then((list) =&gt; {
      console.log(list);
    });
  </code></pre>
  
  <p>This outputs a list of media devices like microphones and cameras. Each device is represented as an object with its own <code>deviceId</code>. But some devices, like one of the microphones in particular, are listed twice. And one time their respective <code>deviceId</code> is set to <code>'default'</code>. What is so special about a one default microphone? And how do I tell which actual <code>deviceId</code> it has?</p>