Never display the Quicktime player X title bar

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It’s possible to hide the title bar within in a Quicktime player X window. The titlebar automatically shows up when the mouse pointer is active in the window. To disable this behavior, quit Quicktime X and apply the following command: 

defaults write com.apple.QuickTimePlayerX MGCinematicWindowDebugForceNoTitlebar 1

Revert to default setting with:

defaults write com.apple.QuickTimePlayerX MGCinematicWindowDebugForceNoTitlebar 0