Why does Qt::WA_TranslucentBackground set on a parent window break the display of video in almost every test case under windows? Doesn't matter what you use to get your video onto a widget.. Phonon, VLC, etc, etc You get a transparent hole with Phonon. You get nothing at all with VLC. The only thing that will work is setting it to full screen which pulls the video from the parent widget making it visible of course or commenting Qt::WA_TranslucentBackground out.