macOS, View for playing Video 4K computer monitor — video only use 25% of it!

In macOS, I defined a View(Hereafter referred to as PlayView) for playing Video!
It's normal in my 'Mac mini (Late 2014)' with many computer monitors, But it's wrong with 4K computer monitor —— The video only use 25% of PlayView!
Width and height of the video are only half of PlayView's! And It happens on some Macs supporting Retina~
macOS, View for playing Video 4K computer monitor — video only use 25% of it!
 
 
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