Voteplayer is an app that manages the music via votes. You can sign in with Spotify or play local music.
https://play.google.com/store/apps/details?id=com.LEEVGS.Voteplayer
The program runs on port 7777. So you should open that port if you want people to connect from outside of your network.
People can open the app and change the ip-adress of the host.
If you opened the port you can see your ip-adress on the following webstite: http://eth0.me/
When you loaded your playlist its important you skip the current playing song in Spotify. The app uses the queue function of Spotify. So when you load the playlist it adds a song to the queue.
The real albums are not loaded for now. But you can add custom albums. Its important you use a _ in the file name.
Example: [Artist]_[Album name]