AudioSwitch

Analog audio switch.
When audio input is sensed, the solid state relay (SSR) is switched on immediately.
After about 5 minutes without music, the SSR is turned off.

Advantage above Arduino version: no software needed and faster switch on time.
Disadvantage: more sensitive to electric noise (does not seem an issue to me).

Documentation can be found here.

Audio switch with Arduino processor.
When audio input is sensed, the solid state relay (SSR) is switched on almost immediately.
After about 5 minutes without music, the SSR is turned off.

The software tries to discriminate between music and a spike on the mains.

Documentation can be found here.
The software can be found here.