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This method works for Call of Duty 1, 2, 4, and World at War
This might work for other Call of Duty games but there are some I do not have.
First you're going to go into a server. Make sure that console in enabled, hit tilda (~) and type /record, and to stop type /stoprecord
For a modded server: (For Windows XP) Get into your COD4 folder, Go to your mods folder...find the mod that the server was using when you took the video...open it, find the demos folder and open that and theres the video.
For non-modded servers: The non-modded servers this is the path, Call Of Duty 4/main/demos
For recording without using the default program you can download a number of third party programs. These programs include fraps, xfire, or anything else that is made to record your screen. To be able to record in Modern Warfare 2 you must use this method! The reason the first method using the /record command will not work is because the game was made with no dedicated servers. This means that the console (~) was taken out because players are not allowed to edit player side settings, and since there are no servers the server side settings were effectively eliminated.
For recording on a console you will need a capture card, or something like a video camera to actually video tape the screen. Using a video camera is not advised because the quality could/is likely to suffer. A capture card will be the best option even though they are expensive because they capture only the screen and the quality is outstanding.