Any one knows how to build the camera ai for replay in a racing game?

Well, *usually*... games try to recreate realism. What you should do, is appoint several "camera" locations around the track.

When replaying the race, you run a quick check from the car against the camera''s to find the closest one. That location will be the base for your OpenGL or DirectX camera. Direction would then be directly aimed at the car.

That would result in the camera showing the car approaching from a distance, quickly turn when it passes the camera, and then follow it a short while, ''till the next camera can catch up.

Oh, and when calculating the distance to the camera''s: use the distance over the track, not absolute distance ^_^

There''s more to it than that.

You want to evaluate the situation. A neck and neck situation between two cars can benefit from an aerial shot usually taken from a helicopter or blimp. There will likely be cameras high in the grandstands as well.

Make use of telephoto lenses as well. Telephoto lenses have narrow fields of view. Don''t put the camera close if it couldn''t be close. That is not the same as using a telephoto lens.

Crashes are likely best filmed side on from a high vantage point. So, if a car crashes into the outside barrier, use a camera from the grandstand on the opposite side in an elevated position using a telephoto lens. The camera should pan as the car slides, tumbles, whatever.

If you are focused in on a particular car, trace a few rays to several points on the car to test to see if its view is obstructed. Evaluate the visibility of the car in the shot for its duration before deciding to use it. If the car was obstructed for more than, say, 25% of the shot, and in any case, no more than 1/4 second, either throwout the shot, or cut it.

Apply this evaluation technique for all of your placed cameras for all the shots. Work on composing a set of shots which tell the relevant story. Let each shot run for at least 1/3 of a second.