Does this mean that High Definition Video evidence of a suspect performing a crime does not constitute very strong evidence of that suspect as guilty of the crime?
Not in and of itself. Evidence of a crime must have strong provenance, that is, people testifying to its history and curation. That's the theory. Whether jurors will be sufficiently sophisticated is a crap shoot - but I'm not prepared to propose anything better.
There was an episode of the TV series Sliders in which the main cast lands in a crime-free world that is obsessed with reality TV cop and court shows. Since the world is crime free, the TV producers stage crimes and digitally superimpose the faces of unwitting perpetrators, then arrest them, try them, and execute them (IIRC - maybe it was just a prison sentence). I'm sure the theme has been used elsewhere as well.
It might at some point, but not yet. This kind of thing would not be feasible enough to do except in extreme circumstances. In the future, as this gets easier to do, it might well become a problem.