air wall pass help

I know how to do it well the steps but I have never done it I lower my FPS to 4 with fraps and it's locked at 4 fps but once I record and I jump on the box and I press it together with my crouch button it doesn't lower my fps right then once I land on the box how do I make it lower it as soon as I press the button?

what do u mean u dont know how to make the FPS to a 4 ?

Yea once I push the button to record it's sopose to lower it to 4FPS and keep it their but it lowers it slowley and I'm sopose to do it once I'm in mid air and it's to slow and once I land on the box a bit later it's at 4FPS how can I make it go to 4FPS as soon as I start recording?(I'm using Fraps)