Many years ago, I read a science fiction story about a guy killing time in a seedy small town movie theater who sees a cheap, amateurish film of a medieval battle. But the protagonist knows enough about both ancient history and film making that he knows that what he is watching is not a cinematographic production, but bad video of a very real event. He deduces that the film must have been made by a time traveler with only amateurish filmmaker's skills, but who has managed to get something on film that simply could not have been shot on a film set or studio--even by an expert cinematographer. Its the real thing! The costumes, crowds, the blood and gore, are not stock Hollywood conventions, they are real. The story revolves about how the film viewer tracks down the director of the film. Ynfortunately, I don't recall much more about the story, but perhaps one of you may remember the name or author.