Am I right in thinking that this is more of a jury instruction/education issue?

The standards of "beyond reasonable doubt" or "preponderance of evidence" don't tell you how much weight to give different types of evidence. If people come to heavily discount any kind of altered, or even alterable, evidence that would address the issue of having this stuff used against someone.

The flip side is not as clear to me: i.e. what to replace these types of evidence with. However, there will almost certainly be technological ways to generate verifiably authentic audio and video.