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?