List output devices
Every speaker the station can play on, from every output plugin, with the mounts each can take
List casts
Every speaker the station is meant to be playing on, each asked how it is doing now
Start cast
Play the station on a speaker, replacing whatever it was playing. The station keeps it playing, through a dropped stream or a restart, until it is stopped here or somebody plays something else on it
Stop cast
Stop the station on a speaker. Answers 204 when it was not playing too