Use a single VLC player instead of one per window

[Cimbali]

To save resources and guarantee a perfect sync between the video in both windows, we should use a single player instance and split the output in both windows.

It does not seem possible out of the box. Relevant topics on the VLC forums:

• Rendering video in two separate windows.
• displaying one video in multible windows
• Bug: No more than one window handle per media player instance can be specified.

  libvlc_media_player_set_xwindow (libvlc_media_player_t *p_mi, uint32_t drawable)
  No more than one window handle per media player instance can be specified. If the media has multiple simultaneously active video tracks, extra tracks will be rendered into external windows beyond the control of the application.

So basically extend libVLC and the python plugin, to use the clone splitter and embed the second output.