great, I managed to create nice looking avi files!!!
The reason why it always captured only upper left quarter of the screen was that even though I run fullscreen, the capturing video size was limited to those values specified in WinUAE settings -> Display -> Windowed section. So, for example, there should be 800x600 if such a screenmode is captured...
Really, the WinUAE GUI wasn't captured as I mentione before. I do not know where did I have this experience from
Here's the
result. Thank you for your help guys!