Just to be clear, it's not app crash, I did not describe it good.
Sometimes fullscreen mode look messy(look at image), let say it's happening every 10th time.
But, I can exit from that messy fullscreen and video plays in normal mode.

I tried:

resize(QApplication::desktop()->width(), QApplication::desktop()->height());

But no effect.

I have Gamma Ray, I guess it can help.
Which informations are relevant?