Zapruder Footage Authenticity

From WFMU's Beware of the Blog: "Here's the alleged stabilized Zapruder film that's been making the rounds. Is it a hoax? A hoax of a hoax? The truth revealed? You decide: [download video: 6.5 meg quicktime file]"

What is interesting to me is that of all the documentaries I've seen, amy of which cover this topic of the assassination pretty thoroughly, none of them have pointed out these discrepencies in the footage. Sure, they may not have anything to do with who committed the crime, but it should definately be considered in any scientific study of the mystery - yet it doesn't seem to receive any attention.