Google Chromecast supports external control, such as play, pause, next, previous using both the Google Home app and an Infrared remote (over HDMI CEC).
How can these events be captured in a custom media receiver (using the CAF Receiver API) when the receiver has no media playing?
When no media is playing, the receiver is in IDLE state - that means that a sender is connected and the receiver app is loaded and running, but there is currently no playback, paused playback or buffering operation ongoing.
The messages that can now be intercepted/observed by the receiver are basically the same regardless if they have been issued by a sender app, Google home/assistant or CEC - and you can process them the same way.
If you want to implement different behavior depending on the device that send the message (or track that maybe), you can have a look at the customData section - you can set up your sender app to include some data into that, but you have no influence on how a Google Home / Google Assistant or CEC issued messages look like: CustomData will be empty here.
