When attempting to watch channels with 5.1 audio (including most HD channels) in QuickTV, if the ffdshow audio decoder is being used, you may get a single frame of video and nothing else. Channels with 2.0 audio (including most SD channels) will play normally.
Solution: open the Audio decoder configuration for ffdshow and check the box labelled Mixer on the left side. Click OK, restart QuickTV, and all channels should now play normally.