The container runs mopidy, which pipes it's audio output to a pulseaudio sink, from where it is sent via an RTP Broadcast on 18.104.22.168:45678.
Plugins for Spotify and a Webinterface are already included.
While this can run on a Raspberry Pi 1, a Raspberry Pi 2 is recommended.
docker run --net=host -e USER='YOUR SPOTIFY USERNAME' -e PASS='YOUR SPOTIFY PASSWORD' malted/mopidy-pulseaudio-server
You can listen to the stream for example with
Navigate your Browser to YOUR_IP:6680 to control mopidy via its webinterface
This image is built for the raspberry pi's ARM architecture, so you can not run it on a Desktop OS.
However you can try to change the "FROM resin/rpi-raspbian:jessie" in the Dockerfile to "FROM ubuntu" and then build and run it on your Desktop.
But I have not tested this, as the project is intended for Raspberry PIs.
You can find the Dockerfile here: https://github.com/Malte-D/rpi-mopidy-pulseaudio-server/blob/master/Dockerfile
If I try to go to
http://localhost:6680 in my browser, I get no response. Is this incorrect? I'm not running on raspberry pi, although that's the next step.