Complex sentence: Despite it being a record-setting fall (only the briefest moment of the beginning of it is used in the movie), the bulk of the fall from the skyscraper as shown on film is clearly of a dummy.
Split into simpler sentences: Despite it being a record-setting fall, only the briefest moment of the beginning of it is used in the movie. The bulk of the fall from the skyscraper as shown on film is clearly of a dummy.