Central to a joyful experience with music and other content is the absence of unpleasant surprises. Your app should not supply the listener with any. You shouldn’t change volume, or groups, or event content without the listener’s express intent. Where possible, your app should inform the user when it’s about to change things.
Very simply, strive at all times to respect the home and the listener.
Users build group configurations to put music exactly where they want it. Your app should not subvert that intent.
Changing the state of grouping for users without explicit or implicit consent.
Do not change the configuration of players, such as into a stereo pair, pairing a SUB with a player, or setting up surrounds, without the user initiating the action.
Now Playing and Playback
Stopping what a user is listening to, or starting unexpected content, is a bad experience. Your app should not do these things.
Do not stop playback without user intent.
Do not play sounds that are not requested by the user. The exception to this is audio ads that play between tracks.
Do not play sound on a player or group at zero volume without the users explicit intent.