Basically, what are the requirements for you to even open a file? I converted a video to mp4 and I installed Quicktime, thinking that was the issue, but it wouldn't even recognize the mp4. When I could open an .avi file, no image would show at all. The entire animation frame was blank. So I uninstalled Quicktime, and now CS4 can't open a file because Quicktime 7 or later is required.
I'd appreciate any help for such a basic question. Thank you!