I have a few automations set up using TTS for notifications (example “The Garage has been opened” when a sensor is triggered.) and it is working fine over my Chromecast audio.
However if music is already playing this notification will stop the music and I am not sure if there is a way to resume playback?
This post is quiet old… I’am grave digging now. Is this problem still persisting for you? If yes, check if the actual process that is playing music has opened the sound card kind of “exclusively”. Dependig on your OS and your sound drivers you should use a device that allows shared (speaking non exclusive) access. For ALSA environments this would be the dmix device for example.