Perhaps:

The red light camera is taking video footage with a trusted and calibrated time stamp.

If you see an object appear in frame in both the red light camera and another camera, you can use this moment to establish a timestamp for the other camera.

So perhaps you see a subject walking in the red light camera (establishing time), but another camera lets you observe details about that subject.

The red light cameras have a trusted time setting. If you can build a chain of video that incorporates the trusted time source, you avoid dealing with and getting testimony from joe homeowners camera.