title: Where can I find APPLICATION_ID
body: <p>I'm learning cast api for android and I'm stuck at this part:</p>
  
  <pre><code>mMediaRouteSelector = new MediaRouteSelector.Builder()
    .addControlCategory(CastMediaControlIntent.categoryForCast("YOUR_APPLICATION_ID"))
    .build();
  </code></pre>
  
  <p>Where can I find this <code>APPLICATION_ID</code> and what is it?</p>