You're right to be skeptical of witnesses, but recordings are also not either/or. Even if you have some sort of digital signature scheme such that a camera can somehow sign its footage and the time and location it was recorded (a scheme that currently is fairly uncommon), how could it encode the circumstance in which the footage was recorded? Who is responsible for maintaining the signature scheme, and why can we trust them? In the absence of any aspect of that scheme, why shouldn't we closely scrutinize video and audio evidence as much as we scrutinize witness testimony?