My older MacBook's graphic card has a hard time with playing 1080 at 100%. Have you tried resizing your quicktime window to half size. If that works, you could drag the window to a larger size that's less than 100% and still works.
1. try using a raid set to play your HD video off of. If you are going to do editing and other work this should be part of your hardware setup. Hd is heavy on the datarate requirement from your drives.
2. don't try to play the H264 files, transcode them to what you find has the best results for the program you are using. You might have to try a few to get the best results. As for me I have an older G5 so I found DVCProHD 1080 60i container (it actually plays and counts frames at 1080p 2398). I have converted these in MPEG Streamclip. If I had an intel mac I would use ProRes.
3. Always copy your files to the harddrive raid. Doesn't matter you can play them off your camera, the camera it using a preview compression so that you can view on your camera.
4. Understand that playing 1080p 2398 requires more horsepower so if your system isn't up to stuff you'll be rendering more and might run into things like dropping frames, crashing out ect. That is why you must first build up your system so that it can handle all this data passing through. It's not like the old days with 24p standard def.
Sorry I know I'm recaping with other things said by everyone in this post but just trying to clear it up for anyone who needs it.
