A transforming performance by Greg Kinnear is at the heart and soul of "Auto Focus," a sympathetic but all-warts film biography of infamously sex-addicted "Hogan's Heroes" star Bob Crane.

It's transforming in the sense of forgetting the actor and become absorbed in his portrayal. But more significantly, it's transforming in the sense of the character's journey from semi-celebrity suburban family man with a secret stash of dirty magazines to compulsive home-porn pioneer who used the very earliest portable videotape equipment to archive his innumerable conquests of star-struck strumpets and call girls.

Kinnear masters the far-off look of a man often living in denial and hiding from his own life. He masters the witty charisma that helped make Crane's TV character a household name, and his later, low-wattage, somewhat needful charm of faded fame.

But with personality-based biopics (as opposed to historical biographies or others films in which the subject accomplished something more than celebrity) the question is, why are you showing me this? "Auto Focus" is an adept piece of moviemaking, produced by the team behind Milos Forman's "Man On the Moon" and "The People vs. Larry Flynt." But Andy Kaufman was extraordinary personality and Flynt became a lightning rod for testing First Amendment law.

Bob Crane was a one-hit wonder TV star with a library of dirty home movies. Is that really compelling enough to justify a feature film? It doesn't seem to be. Although with gifted director Paul Schrader at the helm, it comes close.

With an impressive resume that includes "American Gigolo," "Affliction" and the "Cat People" remake (as a director), and "Taxi Driver," "Raging Bull," "The Last Temptation of Christ" and "Bringing Out the Dead" (as a writer), Schrader has a stylistic mastery of cinema that makes anything he works on worth seeing.

But "Auto Focus" is more of a trivia novelty than is it a memorable motion picture. It does depict with good humor the daring riskiness of the show that made Crane famous. "It's set in a German prison camp!" Crane excitedly explains to his first wife, who replies sardonically, "Oh, with the funny Nazis?"

Every aspect of the film captures strikingly the period in which it takes place -- from the Saul Bass-inspired, swingin' '60s-style opening credits to the very slight touch of ironic self-awareness that accompanies the movie's antiquated video-hound jargon.

Schrader even employs the film's cinematography as a narrative technique, using static, sit-com like shots in early scenes and gradually moving toward the instability of hand-held cameras as Crane's life goes from outwardly ordinary to unstable and increasingly deviant as he took a long, last-ditch dive into dinner theater in his later years.

Almost outshining Kinnear is Willem Dafoe, in a brilliantly volatile turn as swinger and coattail clinger John Carpenter, an electronic technician who turned Crane on to video, became a partner in his sex addiction, and may have been the person who bludgeoned him to death as he slept in 1978.

"Auto Focus" doesn't pull any punches (unless you count some pixelation of Crane's home movies, used to avoid a prudish NC-17 rating) and manages to be both whimsical and somber in depicting the downward spiral that Bob Crane seems blissfully unaware of throughout his life. Kinnear's chipper, wholesome narration is in clever juxtaposition to the story he's telling.

Yet unless Bob Crane is someone of particular interest to you, this film's impressive performances and adept direction aren't likely to leave a lasting impression.