I have had my Nikon D5100 for a few months now, but have just got around to figuring out that the video, when loaded onto my computer, is jumpy. It plays fine on the camera itself. HELP! I have lots of videos of my new son on there!
It sounds more like a memory or video memory issue with your computer. Video files can be quite large and take lot of memory to play. I recommend you close other programs that are not needed when viewing video.
muzza22au recommended VLC because it is more lightweight and doesn't take as many resources as other players.