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