I've been using VP to edit 4K video, downsizing it to 1080p on export. But my PC can't play a 4k video clip (in any program I've tried) without it stuttering, and the audio breaking up. In the VP clip preview window, the audio plays ok, but I constantly get the "Building preview" msg, even with resolution set to a minimum. I'm using a relatively new Dell desktop with I5 processor, 8gb ram, internal graphics, Windows 8.1, 7200rpm hdd. It's just not fast enough. (The final exported result is just