I have a Windows program that uses the Apple QuickTime API to play video. On Windows 7, CPU usage is 100% on one core, which I believe is why the playback is choppy. If I turn on XP compatibility mode for this program, the CPU usage is around 20% of one core, and playback is normal. Using a profiling tool called Very Sleepy (http://www.codersnotes.com/sleepy), I was able to narrow down the high CPU usage to a function in the QuickTime H.264 decoder called JVTCompComponentDispatch. I can't imagine why there would be a difference in CPU usage when XP compatibility mode is turned off or on. Any ideas?