If you have an Nvidia graphics card it has a called Shadowplay that runs very well. VLC media player can actually record from your screen, but performance isn’t as good. The MSI Afterburner software also has a video recording option<–these are all free options. If you want to pay money there’s actually some hardware you can buy that will record which would mean you get full performance on your PC during the demo without having to record at the same time.