Problems with iphone4 video clips after upload to mac and pc

Hi, I'm having a little issue regarding the video I'm taking on my iphone4. Whenever I shoot any footage of anything on the phone, it looks great when I play it back on the phone. But once I upload it to either my MacBook or PC desktop and laptop, the footage appears choppy. The first 2 seconds are okay, and then it'll freeze every 2nd second, to give it a jarring choppy effect. I've used different programs and the problem remains the same. So is it a problem with the phone? Or is there something I can do to help it out? Any feedback would be greatly appreciated!