1. First download 3D Ripper DX http://www.deep-shadows.com/hax/3DRipperDX.htm
2. After installation start it and you can see Please select DirectX8 or DirectX9 application to analize:
3. You'll have to point 3D Ripper to CoD4\iw3mp.exe
4. Click Launch
5. Type in console /devmap mp_yourmap
6. Click F11
7. Have fun !

If you want to get this effect:

You have to record your clip using avidemo NOT fraps because it's not possible.

1. Record normal clip with cl_avidemo for example (200)
2. Start 3d ripper and game trough 3d ripper
3. Our demo is for example mp_crash so type /devmap mp_crash
4. Type /demo YOURDEMO
5. Click F11 and start recording
6. Apply mask to 3d ripped clip add some feather and there u go :)