Desktop Capture Problem

Question

Hi there,
i'm developing a c# application that capture desktop changes and create an avi file.
The application can register in full screen mode or desktop area(region) mode, and all works fine.

But I've a problem with the Frame Rate and Scale (FrameRate/Scale= fps) variables values that distort the real video duration so when i finish my registration the avi file appers so:

Original Value Settings
FrameRate = 25
Scale = 1
fps= (25/1) = 25
WxH=1280x1024
Video lenght = 10 sec

Created File Value
fps = 1.03
WxH=1280x1024
Video lenght= 17-18sec

Anyone can help me?