Taking a screenshot every frame per second and compiling that. + Recording audio and syncing that with images.
The process can take a good majority of your CPU, and most of the videos in Fraps are 3 GB video clips.
IE: I recently deleted all the videos in my Fraps Movies folder. It totaled at 78.54 GB worth of Clips.
Capturing+Converting+Compiling+Syncing+Rendering, Over and over again.