Why such grainy footage from Nikon d3s movie?

I shot some footage outdoors on a sunny day with my nikon d3s in movie mode. ISo was at 200 all day and shutter 1/50 with aperture varying. I'm watching it in QuicktimePro on my Mac desktop and it looks really grainy and low quality. Why is this happening? Do I need a special program to view HD video? Or is it possible that my footage is just grainy? ( but I doubt it, i did several tests beforehand)

Could be quicktime is not handling it properly. Test directly from camera on TV or on another computer and see what gives.
You may also want to talk to nikon support about this.

Quicktime can't handle the Motion JPEG Avi as well as other programs. Try using another program. If I could see the footage, I could tell you more.