How can I save video with Aviwriter-AForge.Video.VFW.dll

Hi

I want to record video.In my project I used webcamcapture.dll for image.
When I use Aviwriter codes an avi files is creating but it is 0 kb and empty.
Anybody know how can I do that.

And my second question
Avi files has very big megabiyte(size) how can I convert for small size?
Or Can I save my webcamcapture video with other writer?

Edit:Sory for my English.