From a legal/evidence perspective, what is going to happen when it will become impossible to tell the difference between a video generated by AI versus the real thing?

I expect that if/when that time comes, we'll see the credibility of video evidence decline.

Currently at my night job, there is video surveillance of common areas. Because of the skill and tools required in doctoring/deepfaking, there's a pretty large window in which footage could be used should it ever need to be. But when we approach the point at which doctoring/deepfakes become pedestrian or even automated, that window slims dramatically.

Depending on the speed and ease with which it can be done, we could see legitimate arguments in favor of discounting video evidence as it then becomes less reliable than eyewitness testimony (which is already notoriously unreliable).