One world's music, synthesised once for every session in it: a Cauldron2D.Audio cued from the world's own state, its PCM sent to every subscriber as {:cauldron_shared_pcm, chunk}.

shared = Cauldron2D.Net.Audio.Shared.fetch(world, MyGame.Client, %{rate: 44_100, channels: 2})
:ok = Cauldron2D.Net.Audio.Shared.subscribe(shared)

fetch/3 finds the world's stage or starts it. The cue is the game's cue/2 of the view its Cauldron2D.Game.view/2 gives for the id :audio, read from a snapshot every two seconds; a game whose view/2 cannot answer for an id that is not a player gets no music from a shared stage. A subscriber is watched; the stage stops a few seconds after its last subscriber is gone, and with the world. A rate change from Cauldron2D.Net.Audio restarts the stage at the new rate.