mpv backend on Windows: unknown address family

[pbienst]

Using version 20201002, the mpv backend, Windows and emacs 27.1.

Whenever I start playing a file, I get

Debugger entered--Lisp error: (error "Unknown address family")
  make-network-process(:name "bongo-mpv" :buffer nil :family local :service "c:/Users/peter/AppData/Local/Temp/bongo-mpv.socket" :filter bongo--mpv-socket-filter)

The file starts playing, but I cannot pause or seek. Only stopping the file works