[apag]

Why would you need VNC?

You only need a browser. On the machine on which you thought you were going to run the VNC client, you open the browser and go to beets’s web UI. Then you pick some music to play, and beets streams it to the browser, which plays it on that machine.

If you actually want the Pi itself to be playing music, then you probably want not the beets web plugin but the BPD plugin, which emulates an MPD server. You can use any MPD client you want to control it – CLI on the Pi, one of the GUI apps over the network, whatever.

No matter what, VNC doesn’t enter the picture.