There should be a remark somewhere in the documentation or wiki that desktop video playback only works under Windows if boolean "lock web items on desktop" in the desktop context menu in "arrange icons by..." is unchecked; since otherwise, the video won't be rendered, turning the desktop background merely blank.
Feature Request:
Automatically check via shell whether web item lock is enabled and give a hint to the user, or turn lock off automatically for the duration of the playback.