The outrageously popular video-sharing Web site YouTube has helped millions of cubicle-dwellers endure the drudgery of a day at the office and even become a player in our nation’s politics. Now the world-changing site can chalk up another accomplishment to its long list: The first motion picture made possible by, purposefully designed for, and largely constructed in tribute to YouTube.

“Hot Rod” is a wafer-thin, empty-headed comedy that seems to be a five-minute YouTube skit blown up to 80 minutes, stretched thin in hopes of grabbing a major league box-office haul. In one notable scene a character even appears to level with the audience, sitting in his bedroom, rewinding through several previous scenes on his computer screen, telling our fretting hero that all hope has not been lost: Their home movie has been downloaded 100,000 times.

But by that moment in “Hot Rod,” about an amateur stunt man who endeavors to jump 15 buses on his minibike, we wish that we were back on our computers, with the option of shutting down. Built entirely around the comedic styling of “Saturday Night Live” regular Andy Samberg, the movie makes fairly clear that Mr. Samberg is not a particularly compelling comedian.

Exhibiting less an original creative spirit than the ability to channel the grown immaturity of Will Ferrell, the blunt infantile rudeness of Adam Sandler, and a dash of hipster arrogance, Mr. Samberg’s scruffy curly hair is vastly more expressive than his face, his mouth, or anything that comes out of it. He’s good in three- to five-minute spurts, as so many “SNL” regulars are required to be, throwing himself into a physical tizzy and then petering out.

One such prerecorded, heavily edited and perfectly mixed spoof, titled “Lazy Sunday,” single-handedly made the ailing “Saturday Night Live” relevant again — primarily thanks to the likes of YouTube, where millions of Americans who no longer watch the ratings-deprived show caught the snippet: Mr. Samberg and colleague Chris Parnell played a pair of white rappers, busting a rhyme about their cab ride to the Upper West Side to catch a screening of the PG-rated family epic “Chronicles of Narnia.” Clocking in at less than five minutes, it was an exceptional piece of comedy, creative in its concept, crisp in its construction, and the perfect length to become a viral sensation in offices across the nation.

It’s impossible not to discuss “Lazy Sunday,” because its international acclaim no doubt punched Mr. Samberg’s ticket to a big-time movie deal. It’s also notable because it gave him fame without demanding of him the same comedic standards that so many other “SNL” alumni have had to meet in order to make their leaps to the big screen. Think of Steve Martin, Mike Myers, Mr. Ferrell — all of them had to develop characters that attracted a following, and had to be able to hold their own during a live, 90-minute weekly broadcast. Mr. Samberg became famous in the editing booth, not due to his live performances, and it shows in “Hot Rod,” as he proves unable to create a character capable of carrying the story.

Lacking Mr. Sandler’s silliness, Jim Carrey’s animation, and Mr. Ferrell’s lovable boorishness, Mr. Samberg’s performance is all over the place. His Rod is at times the would-be daredevil who falls flat on his face, at other times the would-be romantic lead who can’t close the deal, finally the ringleader of a group of losers who seem to revel in their incompetence. The only notion of a plot in “Hot Rod” concerns the daredevil part: Rod’s dad, a stuntman, died before his son could get to know him, and while Rod practices his stunts, setting up makeshift ramps out in the street every day in dad’s honor before crashing spectacularly in true “Jackass” fashion, he learns that his abusive stepfather (Ian McShane) is suffering from a fatal illness.

So Rod devises a plan to organize a new stunt that will raise enough money to pay for his stepfather’s operation. The goal is to get the old man better so that Rod can then beat him in a man-to-man fistfight and earn his respect. It’s hard to tell what’s more bizarre: the sight of dad beating the crap out of his son, or the sight of the son’s body being thrashed and slashed as he crashes his mo-ped into a wall; flies into a moving car, or is set on fire as he tries to entertain children at a birthday party.

Then again, this isn’t intended as an 80-minute comedy; it’s designed as a series of five-minute skits and sight gags that operate independently of one another. If you take a stopwatch to the theater, and have it beep every few minutes, you will see the seams in the structure of ‘Hot Rod,’ the way the random sequences — Rod’s jump over the swimming pool, his fight with his stepfather, his training session in the swimming pool, his improvised dance routine in the forest, his bizarre bonding with his brother in which both repeat the phrase “cool beans” about a hundred times — offer the illusion of movement and structure. But without a solid actor in the lead or a compelling character to have him play, the “Anchorman” randomness doesn’t gel.

During one training scene, Rod stands in place while his friends hoist the family’s drier up on a string, releasing it as it slams into his body and sends him flying. A group of kids are gathered, sitting on their bikes, watching it all. A few giggle, the others just stare, jaws agape. That’s what this movie is — what most of YouTube is, as well — a wacky spectacle that catches us off guard. We look on in morbid fascination, as so many do with car accidents or televised police chases. “Hot Rod” is a momentary distraction, the kind of thing that will be pirated, chopped up, and posted on YouTube in six or seven of its best five-minute clips.

It will probably play better that way.