OS X :: QuickTime X Hidden Preferences (Disable Rounded Corners And More)

To set any of these, go to terminal and enter in the code for whichever preference you want to set. Remember, to reset the setting to its default value, just change the "1" at the end to a "0" (or vice versa).

Disable rounded corners

Code:
defaults write com.apple.QuickTimePlayerX MGCinematicWindowDebugForceNoRoundedCorners 1
Never show titlebar/controller

Code:
defaults write com.apple.QuickTimePlayerX MGUIVisibilityNeverAutoshow 1
Always show titlebar/controller...............