title: How to modify the content of WebRTC MediaStream video track?
body: <p>I use WebRTC in a scenario in which the client video stream is recorded on a third-party server <a href="https://tokbox.com/">https://tokbox.com/</a>. I would like to put some kind of watermark in the recorded video.</p>
  
  <p>Investigation brought me to this page <a href="http://w3c.github.io/webrtc-pc/#mediastreamtrack">http://w3c.github.io/webrtc-pc/#mediastreamtrack</a> and it seems that it is technically possible since it says that:</p>
  
  <blockquote>
    <p>A MediaStream acquired using getUserMedia() is, by default, accessible to an application. This means that the application is able to access the contents of tracks, modify their content, and send that media to any peer it chooses.</p>
  </blockquote>
  
  <p>This is exactly what I need, but I didn't find any examples or explanation of this function. I'd like to get some advice from WebRTC experts.</p>