title: WebRTC replaceTrack, getStats not returning audioInputLevel
body: <p>I have a WebRTC stream which is sending audio/video, I am displaying the volume in a meter widget which is retrieved from a <code>getStats</code> call on the peerConnection.</p>
  
  <pre><code>getStats(function (stats) {
    var results = stats.result()
    for (let i=0; i &lt; results.length; i++) {
      var res = results[i]
      if (res.type == 'ssrc') {
        volume = parseInt(res.stat('audioInputLevel'))
      }
    }
  })
  </code></pre>
  
  <p>This is working fine, the issue is when I run <code>replaceTrack</code> to update the streams audio/video the above <code>getStats</code> returns 0 for the audio level.</p>
  
  <pre><code>navigator.mediaDevices.getUserMedia(media)
    .then(stream =&gt; {
      const tracks = stream.getTracks()
  
      peerConnection.getSenders()
        .forEach(sender =&gt; {
          const newTrack = tracks.find(track =&gt; track.kind === sender.track.kind)
          sender.replaceTrack(newTrack)
        })
    })
  </code></pre>
  
  <p>The local stream get's updated, the remote user get's updated and audio / video is working. But <code>getStats</code> is no longer returning the <code>audioInputLevel</code>.</p>
  
  <p>Would anyone be able to help me understand why? Or what a fix maybe.</p>
  
  <p>Thanks</p>