Can't set background on QVideoWidget when framelesswindowhint is set

In Media Player out of examples, I set WindowType with Qt::Framelesswindowhint. 

As I attached image videowidget become transparent. 

I think that this single code does not work on Qt 5.11.2 anymore

->    setAttribute(Qt::WA_OpaquePaintEvent);

This code in videowidget.cpp

Moreover, I add my customized title bar like that situation. I do maximize followed by minimized followed by restore window then hover does not work. 

p.s. I got QVideoWidget does not call paintEvent() even when I call update() explicitly.