My Raspberry Pi can turn audio gears on and off via relays.
When my desktop starts using its speakers, I want it to tell Raspberry Pi
to turn on the speakers via a relay.
When nothing has used the speakers for a minute, I want it to tell
Raspberry Pi to turn off the speakers.
I can do the same for a USB microphone. A USB microphone can be turned on
and off by uhubctl.
Does ALSA have a callback API that I hook into? Does jack have it?