I do something similar with chromecast_mpris. I have my media keys mapped to Plasma's Media Controller, which uses MPRIS in the background. Works well for me, a

I do something similar with chromecast_mpris. I have my media keys mapped to Plasma's Media Controller, which uses MPRIS in the background. Works well for me, and you don't have to wait for catt to launch and find your Chromecast each time.