What is it???

Bullet time is the registerd trade mark of warner bros.(Matrix's distrubitor) and refers to the digitally enhanced stimulation of variable speed photography used in films, adverts and even video games. Basically it is a type of slow motion or time lapse technique. However it allows the you to film imperceptible and un-filmable events, such as bullets. It also allows the point of view of the viewer to move around a scene at normal speed while the objects in the scene are slowed down.

Bullet time was originally achieved photographially by surrounding the subject with cameras. these would then take a pictures simulataneously or sequentially depending on the desired effect. the frames would then be arranged and displayed in sequence to create a orbiting viewpoint.
For many years, it has been possible to use computer vision techniques to create and render scenes with novel viewpoints sufficient enough for bullet time type effects. More recently, this has been formalised into what is none as free viewpoint television (FTV) which is bassically the live action version of bullet time.
Bullet time within the Matrix was pre-designed using CGI, which was then used as a guide to set up cameras on a track using laser targeting behind a green screen creating a complex curve through space. The cameras were then triggered at very close intervals from different viewpoints to create extreme slow motion. the frames were also scanned by a interpolation software to create even more frames to slow it down further and increase fluidity. They could also drop frames to speed up the action.