cpiped captures an audio stream and outputs it to a pipe with a bit of buffering to handle clock mismatch. It also includes silence/sound detection and the ability to run a command on detection.
I'm using this to capture line-in audio from a sound card and send it to forked-daapd (https://github.com/ejurgensen/forked-daapd). On sound detection, it runs a simple script to start playing the associated pipe in forked-daapd.