Hardly faithful at all, and it was never intended to be. This film version, which is mostly silent, is based on Edna Ferber's novel (from which the musical was adapted), and was put into production as a silent film before the musical became such a hit on Broadway. When the 1929 film's producers realized that the public was probably expecting a talking film version of the musical, they panicked and shot a 17-minute sound prologue to be shown preceding the actual film, with some of the musical's original Broadway cast members singing five songs from the show. Then they added two musical sequences in which Magnolia (played in the film proper by Laura La Plante, with a dubbed singing voice) sings two songs from the show. One of these songs ("Ol' Man River") Magnolia never, ever sings in either the stage version or the 1936 and 1951 film versions.Although some of the plot is the same, the script of this film is entirely different from that of the musical version and the films adapted from it.The storyline follows the plotline of the novel, rather than that of the musical, which means that the film is sometimes drastically different from the show. The scenes with Julie on the show boat take place when Magnolia is still a little girl, instead of her being eighteen years old as in the musical. Magnolia does not meet Ravenal until more than ten years after Julie and her husband leave the boat, instead of on the same day. Magnolia's parents (Captain Andy and Parthy) both die in this film; he, in a storm during which Magnolia's daughter Kim is born. Parthy dies offscreen near the end of the film while Magnolia is in New York with Kim. In the musical and the 1936 and '51 films of "Show Boat", none of the characters die.There are three major changes to the Ferber novel in this film - one is that Julie is a white woman whose marriage is perfectly legal in this version, not a mixed-race woman illegally married to a white man as in the novel and the musical, and she is driven off the show boat by the jealous Parthy, who resents Julie and Magnolia's friendship, not, as in the novel and the musical, because of the racist laws existing at the time.The second major change is that Ravenal and Magnolia are reunited and reconciled at the end of the film, as in the musical, while in the novel, he never returns after abandoning Magnolia and eventually dies in San Francisco at some point.The third major change is in the depiction of Hetty Chilson, the whorehouse madam found in the novel, but not in the stage musical or the 1936 and 1951 films made from it. In the 1929 film, Hetty turns out to be Julie herself, unexplainedly now assuming a new identity. In the Ferber novel, Hetty is a different person from Julie, who is her secretary at the whorehouse. In both the novel and this film, Magnolia discovers that Julie works at the whorehouse, and rather than judging her, offers her friendship, but Julie is so deeply ashamed that she cannot face Magnolia.
It has never really been made clear. When the film is shown on television, there is no picture during the sound prologue. However, two sequences from the prologue which are NOT in the Turner Classic Movies version of the film have turned up on the internet with sound and picture; they are also included as clips on the A&E biography "Great Ziegfeld". Although the picture for the story section of the film seems to have survived complete, there is supposed to be a sound sequence of Magnolia singing the traditional spiritual "Deep River", but so far there is no evidence that this sequence has survived or even once existed. During the first half of the film, we see Magnolia with a banjo, but the sequence as it exists now is silent with orchestral accompaniment.There are about seven minutes of dialogue in this portion of the movie as it exists today, but then the sound cuts off, with not even a musical accompaniment, indicating that what we are watching was originally issued with a soundtrack. Reportedly, some of the soundtrack for this portion has recently been rediscovered on discs, which is rather odd considering the fact that the film used the Movietone system, a system placing the sound on the film rather than on a disc.