screencap problem

I capped quite a few times with kmplayer and never really had a problem. Now I'm trying to cap a video that's about 4 min long. I said I wanted 3 caps in 1 sec. But first off it took a long time before he was done. And then I found out he made 7.000 screencaps. Even if I say 1 a second he still makes about 1000 screencaps?

Is there something wrong with me video file or something?