Breaking changes between libvlc 3 and libvlc 4:
- libvlc_media_player_will_play() is removed (it is meaningless with the
  new player)
- libvlc_media_player callbacks are called with the same (recursive)
  mutex as libvlc_media_player functions
- libvlc_media_player_stop() is now asynchronous
- libvlc_media_player_set_pause() and libvlc_media_player_set_media(), which
  could possibly stop, are now asynchronous too
