title: How to join an existing activity playing media in chrome app
body: <p>So assuming you've already launched media on the receiver from an iOS/Android/Web app, how can another web app join this activity and control the media? I noticed that the cast API has a 'JOIN_ACTIVITY' in it, but there's nothing that currently uses it. Nor do you know the activity's ID to join it..</p>
  
  <p>This is similar to <a href="https://stackoverflow.com/questions/18219184/how-to-check-if-a-chromecast-session-is-already-in-progress">How to check if a ChromeCast Session is already in progress</a> however, this answer does not help to connect to an existing application</p>
  
  <p>However, using the javascript API, even if you know your app is running I can't find a way to connect to it without re-launching</p>