I've been using the Obsidian skin in Theater View along with the Grey Vines background video from sirganty's MetroX skin (
http://yabb.jriver.com/interact/index.php?topic=79340.0). I like it a lot, but I was in the mood for a change.
I found this YouTube Channel with ~500 different background videos:
http://www.youtube.com/channel/UCQP6qJU1vAq7fINZtHYfnJQ/videosAll you need to do is to download a clip of your liking. I know for sure .mpg and .flv files work, the .mp4 ones I tried did not work (you can always use MC to convert format as well).
Create a New Folder in C:\Program Files (x86)\J River\Media Center 19\Skins\Theater View\Themes and name it for your new clip.
Rename your downloaded clip "Background" and copy it into the Folder you just created.
Under Tools -> Options -> Theater View -> Appearance -> Theme select the name of the Folder you created.
Voila .... a new moving Background image in Theater View. Seems simple enough, but I never thought to try it until today. Thought others might enjoy it as well.