I asked this question on the PyQt mailing list, and didn't get any responses, so I'll try my luck here.
I've encountered a frustrating issue (on Windows only): when trying to create a VideoWidget instance, I'm getting the error message "the video widget could not be initialized correctly". Oddly, this just surfaced in the code after several weeks of perfect operation, on two separate Windows boxes (one Vista, the other an XP image running via Parallels). I'm not aware of anything having changed in the environment that may have caused it.
I'm using Python 2.6 and the PyQt 4.5.4 Windows installer. I notice this issue was raised last November, but no solutions were offered:
http://www.riverbankcomputing.com/pipermail/pyqt/2008-November/021029.html
My Googling hasn't turned up any explanations of what may cause this. Can anyone clue me in?
Hate to answer my own question, but if anyone else encounters this:
The solution to this ended up being hardware-specific. Phonon appears to have issues with the video drivers for particular virtual machines - Parallels in my case. Physical hardware doesn't exhibit the issue. There is no workaround I've been able to find.