I appreciate your answer. The " completely " means that the desktop is totally covered by another window, like another window maximizing. Because the video wallpaper is actually a window that have window.level = NSWindow.Level(rawValue: Int(CGWindowLevelForKey(.desktopWindow))) Then just put an AVPlayerView in this window, the video wallpaper is done. This window will always stay on desktop and will not cover any other window. And go back to my question. When user maximize other window(such as Safari), the desktop is cover by this window. It is time to stop the video play on that desktopWindow So I want to know if there is any notifications or methods that can let me know there is a maximize event occur in other windows so I can use the video play on that desktopWindow