Fraps runs fine for an hour or so, then the framerate crashes

Well turns out I discovered the answer to this myself.

Fraps heavily writes to the HDD, and slows down the game if it can't write the videos fast enough. For me, this was because my HDD was becoming rapidly fragmented as Fraps ran over long periods of time (about 10% after 1 hour). This was causing Fraps to not be able to keep up with the action.

From my research, there are two fixes to this:

• Record to a second HDD dedicated to Fraps
• Set Fraps to record at a lower resolution or lower framerate. For instance, record at 30fps, but turn off framerate lock so the game isn't reduced to 30fps (probably the best solution).
• Take a break every time Fraps decides to slow down, and defrag your disk.

I hope this helps someone out in the future!