HTML5 video supported but no codec is found.

I'm using a fresh install of Qt 5.0.1 Visual Studio 10 from the official build.

I'm developing an application that uses webkit, webkitwidgets, multimedia and multimediawidgets.
When I play a local .mp4 video file using QMediaPlayer the playback is good, however, when I try to play a HTML .mp4 video inside a QWebView widget, it just doesn't work.

Websites tell me that my browser (webkit-QWebView) supports HTML video, but the codecs are not being found. I think the webkit uses multimedia for video support, so maybe there is a fix for this.