title: Is MediaInfo.Builder's contentId always a URL?
body: <p>In the <a href="https://developers.google.com/cast/docs/reference/android/com/google/android/gms/cast/MediaInfo.Builder.html#MediaInfo.Builder(java.lang.String)" rel="nofollow">Chromecast Android docs</a>, the argument to MediaInfo.Builder is called <code>contentId</code>. In every example I've seen, <code>contentId</code> is passed a URL. Must <code>contentId</code> be a URL, or are there other ways to address content?</p>