Valve released their in-house Source Filmmaker to Beta today. The software suite was used to create many of the videos used to promote Valve's software over the years, including today's premier Meet The Pyro.
Essentially, Filmmaker allows you to make a highly detailed movie out of any source game, turning the game world into a movie set and making you the director. Valve's Bay Raitt explains at length in the video above just how that works. Valve writes in the introductory post:
Because the SFM uses the same assets as the game, anything that exists in the game can be used in the movie, and vice versa. By utilizing the hardware rendering power of a modern gaming PC, the SFM allows storytellers to work in a what-you-see-is-what-you-get environment so they can iterate in the context of what it will feel like for the final audience.
While I can't see myself ever using the software, I can't wait to see what the dedicated Valve community comes up with.