before modern tech, justice relied more on witnesses than documents and recordings. 

It has advantages, but one reason that it worked, is that pp were less likely to perjury than today. 

back into middle ages they had really surprising laws, trusting pp more than physical evidence in surprising ways. 

what will happen if we lose the ability to rely on a video or sound recording as proof of anything, and anyone powerful/rich enough can have for dozens of false witnesses? 

not even entering in politics (that may go into full hallucination mode), just about the usual justice system.