There is a lag between the two frames when capturing a screenshot. I said, it doesnt influence the gameplay when the interval is long enough and the screen resolution is not too high. I doubt that the ingame screenshot function is fast enough (or your PC) to capture realtime videos. Maybe you can log the whole screenplay and replay it in a lower speed capturing everything.. but then sound is missing as well. Try for ingame capturing FRAPS or similar. (or better: capture it with a DVD recorder, you get no speed disadvantage when you split the VGA signal and record it on a DVD! Later you can cut it very well. So you can play 1 hour without caring disk space or game performance).

Bye
Christian