Xvid "jerkiness" in video?

Hello, I've recently come across several Xvid files with video "jerkiness" or unsteadiness problems. Every few seconds the video seems to catch for a brief fraction of a second and then continue. It's not a media issue, since the same thing happens whether I play the files on my PC or from dvd on my Philips DVP642 player. It's barely noticeable, but definitely there. There doesn't seem to be a corresponding audio catch since even music in the background plays smoothly. The video quality otherwise seems to be fine. I have now about three files of this type, each about 700MB, and am wondering if there's something I can do to "smooth out" the video. Thx.