The problem can be reproduced with the qmediaplayer demo. If all the audio devices are disabled (from Control Panel\All Control Panel Items\System\Device Manager) playing an .avi file will result error:

"The operation cannot be performed because the pins are not connected. (0x80040209)"

The same .avi file can be played with Windows Media Player without any problems. The qmediaplayer shows a .wmv file correctly when the audio devices are disabled.