Line In support

I’d love to have the option to play back music from a device plugged into the sound cards Line In connector.
I looked into writing this myself, but I’m honestly at a loss just figuring out how to get started writing an extension, having never tackled more than small, stand-alone scripts in Python before.

EDIT: Really, all I’d need for that is a way to run a command line script from a web-interface. It doesn’t have to go through the mpd or show up in a playlist.
Just have a seperate button in the web-interface that says “line in” and when you click it, it pauses the mpd and does some command-line foo (for alsa or pulseaudio) to pipe the line in to the line out.
Click again (or click on something else?) to revert. would be the ideal way to do this. But there isn’t a way to give GStreamer an URI which would make it use that src.

So don’t really see any clean or simple way of adding anything like this to mopidy itself.