Machinima

Machinima is a type of CGI filming style, using pre-rendered models from video games. Red vs Blue is a popular Halo 1 and Halo 2 machinima. Other popular Halo machinima include The Codex and Fire Team Charlie.

Another definition of machinima is posted at halomovies.org:

"Machinima (muh-sheen-eh-mah) or machine cinema and/or "machine" "animation", is both a collection of associated production techniques and a film genre. As a film genre, the term refers to movies created by using tools and resources available in a commercial game engine. By combining the techniques of filmmaking, animation production and the technology of real-time 3D game engines, Machinima makes for a very cost-and time-efficient way to produce films, with a large amount of creative control."

Machinima in Halo: Combat Evolved, such as Red vs. Blue (seasons 1, 2, and 3 before the Halo 2 Saga), was filmed using the pistol and panning using editing software. In the Halo 2 Saga, it was filmed using a glitch. This glitch gives you no weapons. All that was left was to edit out the radar and the HUD.