The Open VTT - Music Player Feature Pack is what it sounds like, it adds the feature for you as the host of a OpenVTT session to play music to yourself and your players.

You can use this feature by opening up the new Music Player Tab on your right and pressing play on any of your music assets, if you don’t have any added yet, then just head over to your asset tab and add a music asset, note however that the player can only play mp3 files.