c# coding to add user specified screen recording to app - repost

Reposting as selected coder didnt read brief and accepted job to do then told me would be in delphi. It has to be in c#. Basically I need a screen recording app. that works similar to camtasia without the bells and whistles. Essentially allowing recording of desktop area, user will draw or select an application, and this will give option of recording sound (from whatever sound sources available) and it will save file to flv or mp4 in the max res that its recording in. Happy for it to use ffmpeg. Please show a demo before demanding big money. This should be pretty straight forward.