Getting a lot of banding when playing video with a QGraphicsViewItem

[Zapfyr]

I have been playing around a bit with the QGraphicsVideoItem in QT 5.1.0 in Windows 8. And for some reason I get a lot of banding in every video I play. When rendering an image with a gradient no banding occurs, which should mean that the issue is not with the scene or view but with the actual rendering/decoding of the video.

My test scene, where I render one 720p H264 coded video as a background, an image (the gradient) and the trailer of The Hobbit (1080p H264).
!http://tux.servegame.org/~zapfyr/Screenshot_banding.png(Test scene)!

How one of the videos looks when played in VLC.
!http://tux.servegame.org/~zapfyr/Screenshot_non-banding.png(Video played in VLC)!

Some movies works better than others I have tried a bunch of different coded movies. Where Theora does not work at all (black) while MPEG4 and H264 gives a lot of banding and in some cases just blinks and produce some artifacts. The only video I could render without problems where a video coded with Microsoft MPEG-4 4.2.

Does it use Windows Media Foundation? And if so how do I add better codecs to it? I want to be able to play as many different coded movies as possible, but it would be fine if H264 or MPEG4 worked well.