I was getting frustrated when no matter what I did I couldn’t see the background video running in my Adobe Encore cs4 title menu preview.
I searched hi and low, and the only thing I could find said I had to remove all graphics from the menu for the background video to work (this is completely untrue).
Finally, I discovered that when you are looking at the preview window in Adobe Encore, there is a little “disc” icon with an arrow pointing to the right in the top row of the preview menu on the far left hand side. Click that icon, and the background video is rendered so that you can see it in the preview.
I put all my text and graphics back in the menu (using Photoshop), and it still works flawlessly.