What is wrong with FPS displayed by FRAPS?

[Gandalf the Golden]

I start the game, ask FRAPS to record at 60 FPS. The game sometimes go down to 50 FPS, but when I go to see the recording, it is at stable 60 FPS!
This is too good to be true, so, what am I misunderstanding?

 

[Promethor]

Fraps put a lot of stress on your system. It need to record in real-time at 60 fps while your video card and CPU are allready working hard to render your game.

Your game slow down to 50 fps because your hardware cannot keep up to record at 60 fps and playing a game at 60 fps at the same time.

so; - Fraps record at 60 fps, but your game slow down at 50 fps.
`You actually watching a video at 60 fps of a game played at 50 fps.

 

[RobiePAX]

Promethor is partially right, but still wrong. When in-game framerate goes below the target framerate during recording it means that computer simply can NOT record and render at that much framerate, as result it goes below that value. But the MOMENT you see lower value fps during recording than your set target is, it means video is generating dropped frames.

Dropped frame is when capture software failed to capture the frame in time so it skipped it and proceeded to the next one, as result making previous frame to repeat itself, making it look for you that video "paused" for a moment or as we call it "lagged". More dropped frames = more lag.

What makes you think when you are playing back the video it's stable 60 fps? Did you analyse the number of dropped frames in it?

 

[Gandalf the Golden]

In fact, the FRAPS FPS counter in the video is 60, while in-game, while recording, drops a bit.
However, I can still notice the lag I had in certain moments of the game I was recording when I watch the video...