Combat Arms has gotten a new content updated called Operation: Dredge, and with it comes the ability to capture video inside the game and upload it seamlessly to YouTube. For most PC games this process usually requires a third party program to run, some of which actually costs extra money. Also included with the update is a new versus map as well as a set of weapons from the FS2000 family.
The process looks fairly painless, you just need to enable the capture settings before a match and then press a hot key to start and stop recording at anytime. After the match you are given the option to upload the video to YouTube if you wish. This should work for any game type including the various co-op modes the game supports.
Detailed, step by step instructions, on how to utilize the YouTube video capture support is available at the Nexon site.