Does the script work in the terminal (command-line usage)?

[ghost]

Shift + Enter progresses to the next track / playlist entry when running mpv on the command-line, no mpv-playlistmanager's interface appears. The script functions correctly in the mpv window (which I prefer not to launch when playing audio).

I exclusively play audio with the mpv's --no-video flag (disables video playback, the mpv windows isn't created) and more or less always launch mpv (add files to a playlist) via the Unix shell.