Why is Phonon so slow?.

[DaveyDave]

Hi All,
I'm using the Phonon plugin to play a wmv video file in a QT application. I'm running this on Windows 7 using a DirectX backend. The playback is very jerky even though the video is low resolution. Playing the same video using Windows Media Player is fine.

On the basis that the Phonon plugin is using a DirectX mechanism underneath why is this happening?. Has anyone any ideas how to improve the performance of the Phonon VideoWidget?.

Thanks in advance,
Dave