My setup consists of two Symfonisk speakers, stereo paired, and a Sonos Port. The Port has a line in from a Behringer sound card. The card is fed by a Raspberry PI and also has an analog line-in signal from the TV.
I have set the Port to Autoplay line-in. When I start a film on Netflix (Chromecast connected to TV), the port is activated and sound comes up within two seconds through the Symfonisk speakers, which is good enough.
However, if there’s a silent passage in the film, sound gets deactivated and it may take 5 seconds to activate again when signal is detected. Looks like Autoplay gets interrupted after a couple of seconds with no sound. Is there a way to prevent this from happening, other than manually switching input via the Sonos app?