Hello, i have a brand new, i5, HHD, And 4 Gb Of Ram, macbook pro

when i run a video on quicktime it chops frames... meaning it will play smoothly, and than skip. i've checked the ram, and more than half of it is avaliable, also, my cpu is only running at 20%.

i don't have any other programs open either, but it still skips.

the video i am using is 720p filmed at 60 frames per second.

Please Help Me With This