This is a demo of OpenTSPS (opentsps.com) working directly with Unity3d (unity3d.com).
This video tracks one person from a security camera as they walk through a lobby. Their position is represented by a cube and mapped into the 3d game world.
unity3d example project and source code is available here:
The video is borrowed from the CAVIAR video set:
which has a bunch of great videos for computer vision tracking and testing