VLC can only play video files formats from the web (.mp4, .mp3, .avi, etc.). The external player is a .html file, meaning that it's a website, not an actual video file, and thus cannot be streamed through VLC. If youtube has a way of playing videos through VLC, then try that, but it still may not work since the external youtube players is specially hooked into DeepBot to be able to change the video when new songs are requested.