Well.... The book is based on a single perspective also -- that of the person collecting the interviews -- an employee of the United Nations Postwar Commission Report. Somewhere (can't seem to find it now), I read the opinion that all the interviews are in the "same voice", which I understood to mean that the book would've been better if the author had done a better job of giving each of the interviewees their own unique voice.
According to the Wikipedia page about the movie
, the Brad Pitt character in the movie represents the interview collector (i.e., the narrator) from the book. The book provides very little information about the narrator as a person. My impression is that the movie provides more personal detail about the narrator in order to give the viewer a central character to identify with (see the Straczynski quote below).
A clear difference between the book and the movie is that the book describes interviews collected after the war. The movie apparently is about the narrator's activity during the war attempting to help the war effort:
So, I think there will be some difference between the book and the movie, but I think they may be closer in spirit than is clear from the trailer.