Machinima is a type of CGI filming style, using pre-rendered models from video games. Red vs Blue is a popular machinima made using using all three Halo games.
Machinima in Halo: Combat Evolved, such as Red vs Blue (seasons 1, 2, and 3), was filmed using the pistol and panning using editing software. In the Halo 2 Saga, it was filmed using the gun-drop glitch, which left only the the HUD to be edited out in post-production.
The Theater lobby, or saved films feature in Halo 3 presented a large advantage to machinima makers.