If you start Ensemble from GA bundle and go straight to the Adv Media demo using the navigation tree and mouse click, the media will not play until another node is selected then go back to the Adv Media demo.

Steps:
Launch Ensemble from GA bundle
Using the mouse adjust the tree view and select the Advanced Media demo
Press play, nothing happens
Using the mouse choose another node
Now select the Adv Media node again and the media will play