It's like Source Recorder. You record a demo file - just like recording with Fraps, but it tracks everything's movement in the recording. You can than play it back in Blockland. It's like the Replay feature in TF2. Afterwards, people can slow down the demo if they need to, and record the demo and have the frames exported as an AVI or thousands of TGAs, then compress them into a video to be uploaded to Youtube.
