Cadmanpro
You need to play around with your frame rate.
When you record your MPEG, you have three options: 25, 30 and 50 Frames per second (FPS).
So if you are recording your MPEG at 25 FPS, you need to make sure that the animation or motion analysis is also recorded at 25 FPS to ensure that the animation is running on a 1:1 time scale.
If you want to slow it down, you can record your motion analysis with a higher frame rate. It will still cut to the MPEG at 25 FPS, except it will seem to be moving slower, since the steps between each frame are now smaller.
Hope it helps!