 There is a way to tell when Vito Corleone is speaking whether its  Marlon Brando or an impersonator. If the voice sounds scratchy and  weary, its Brando. If the recording sounds clean, its the  impersonator. Also, there is a scene in which the real film dialog  is used: In the scene where Tom Hagen tells Vito Corleone that Sonny  is dead, its the real movie soundtrack.