Thanks for the hint Nicholas. But, command-Y is another shortcut for quick look. And, you will notice in finder if you have the quick look icon in the toolbar that pressing the option key changes the quick look image to a play button. So, command-Y is quick look and command-option-Y is playback (quick look fullscreen). But, command-option-Y does not go from normal quick look view of a file to fullscreen, which is what I thought you were saying.