read directly from the video card framebuffer

hi!

Is it possible to directly read the video card output and save it into a file 
as a screen shot?  I have to capture for a long time the display. Doing it 
making screen shots is not a good solution. That why I'm trying to find out 
how to capture the video card output. How can I record the screen as a movie 
file without making screen shots?
 
thank for your help
 
james