Code: defaults write com.apple.QuickTimePlayerX MGCinematicWindowDebugForceNoRoundedCorners 1

Code: defaults write com.apple.QuickTimePlayerX MGUIVisibilityNeverAutoshow 1

Code: defaults write com.apple.QuickTimePlayerX MGUIVisibilityNeverAutohide 1

Code: defaults write com.apple.QuickTimePlayerX MGCinematicWindowDebugForceNoTitlebar 1

Code: defaults write com.apple.QuickTimePlayerX MGPlayMovieOnOpen 1

Code: defaults write com.apple.QuickTimePlayerX MGEnableCCAndSubtitlesOnOpen 1

Code: defaults write com.apple.QuickTimePlayerX MGFullScreenExitOnAppSwitch 0

Code: defaults write com.apple.QuickTimePlayerX MGAllowMultipleSimultaneousRecordings 1

Code: defaults write com.apple.QuickTimePlayerX MGTimeIntervalBeforeShowingLoadingUI defaults write com.apple.QuickTimePlayerX MGUseForkedDecoder defaults write com.apple.QuickTimePlayerX MGEnableMediumQualityAudioRendering defaults write com.apple.QuickTimePlayerX MGDisableQuickTimeX defaults write com.apple.QuickTimePlayerX MGShowFrameworkVersions defaults write com.apple.QuickTimePlayerX MGEnableWWDC2009KeynoteBehavior defaults write com.apple.QuickTimePlayerX MGCinematicWindowUseWindowShapeForRoundedCorners defaults write com.apple.QuickTimePlayerX MGCinematicWindowTitleAlwaysHasActiveAppearance defaults write com.apple.QuickTimePlayerX MGTimelineDisableAudioTrackForVideoMovies defaults write com.apple.QuickTimePlayerX MGTimelineShowSlientRangesWithModifierKey

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).I don't know exactly what these do, or they don't seem to have an effect when I enable them but here you go: