Zapruder said in the Clay Shaw trial that the film shown to the jury (multiple times) was the same one that was developed in Dallas the day of the assassination. The trial film was one of the copies made by Time/Life that was subpoenaed by Garrison. That copy was bootlegged and released to large parts of the public.
From the trial:
Q: Mr. Zapruder, from having seen what was projected on this film, can you tell the Court whether or not it appears to be the same as you viewed your original film on November 22, 1963 in Dallas, Texas?
A: Yes, it does.
It seems obvious that if large parts were cut out or changed that he would have noticed it. Maybe not but we have lots of other evidence that is, for me, persuasive that the film wasn't deliberately altered.
The rest of his testimony is here: http://www.jfk-online.com/zaprudershaw2.html
Zapruder was Unable to ID Himself on the Zapruder Film Still Frames shown to him during his WC Testimony. Now, years later you want to swear by him when he is viewing a film in the middle of a packed courtroom? Zapruder was paid $150,000 for his film. This $150,000 would make it difficult for him to discredit an alleged copy of the film he sold to Time/Life for a small fortune. In 1963 when Zapruder sold his film for $150K, the average American was making roughly $4,000. $150,000 was a Ton of $$$ back in 1963.
