The Google Cast API was updated today with some good changes. Most notably is that it now officially supports 4K casting. Also included in the changelog is that the API supports maintaining a state of cast session, where the new class holds the current status of the stream, a fix to the image aspect ratio, ad breaks, and remote control notifications.
That last addition sounds like an interesting one. Whenever a user is casting, other devices on the same network will get a notification that will allow them to control playback, too — something that I cannot imagine ever going wrong. The primary user can disable this feature in the Settings app under the "Google Cast" section, though. Obviously the major takeaway from this changelog is the addition of 4K to the Cast API, which we should see implemented by third-party devs in the near future.
- Google Developers