If you are really looking for a screencast, then you can always go for software such as screen-capture-recorder-to-video-windows-free and virtual-audio-capture-grabber-device which are free and open source. If you want to see how it works before trying it out, you can visit this tutorial.
The basic logic behind these is that they use ffmpeg2 which in turn uses 'screen-capture-recorder-to-video-windows-free' for its video input and 'virtual-audio-capture-grabber-device which are free' for its audio input. Both of these are configurable. The tutorial shows how smooth the recording goes. These software also provide a UI (developed in Java) for changing settings as suited to the user.
e.g use (from command line):
ffmpeg -f dshow -i audio="virtual-audio-capturer":video="screen-capture-recorder" ScreenCast.mp4