As soon as word of Tristram Shandy: A Cock & Bull Story began circulating, a directive from the Movie Writers’ Guild decreed that the film’s source, 18th-century writer Laurence Sterne’s The Life and Opinions of Tristram Shandy, Gentleman, be described as “unfilmable.” But all novels are essentially unfilmable, save for examples of those contemporary genres—thrillers, chick lit, detective yarns—that tend to be merely screenplay treatments in drag. In fact, Sterne’s novel may qualify as more filmable than most: Its playfully self-conscious approach to narrative suits the many ways a winking filmmaker can frame a facetious tale. All of the book can’t be put onscreen in 90 minutes or so, but its digressive tone can be amusingly simulated.

Tristram Shandy director Michael Winterbottom begins winking and framing, opening the film with actors Steve Coogan and Rob Brydon playing some version of themselves and discussing such vital issues—to actors—as tooth color and billing. Winterbottom and pseudonymous scripter Martin Hardy take the story backstage because that’s what Sterne did with his near-endless asides about the nature of storytelling. The point of the novel is never to get to the point, which the movie respects as best it can.

The principal precedent for Tristram Shandy is 24 Hour Party People, a semi-historical account of Manchester’s postpunk scene. As in that self-conscious romp, Coogan is both the central character and the onscreen narrator, explaining the story as he acts it out. This time, however, there’s barely a story: Shandy observes the preparations for his birth as his father, Walter (Coogan again, outfitted with a fake nose), and mother, Elizabeth (Keeley Hawes), battle over where and how the not-so-blessed event should transpire. Meanwhile, Tristram’s uncle Toby fools with his pipe, recreates the Battle of Namur, and romances Widow Wadman.

When the cameras supervised by onscreen director Mark (Jeremy Northam) aren’t running, “Coogan” comments on the difficulties of casting the film-within-a-film, contends with the visit of girlfriend Jenny (Kelly Macdonald) and their newborn child, and considers having a fling with Jennie (Naomie Harris), an earnest production assistant.

Then there’s the matter of a one-night stand that “Coogan” had with a stripper who now wants to sell her story. To forestall this possibility, the actor agrees to an interview with a journalist from the paper that’s been offered the story of his indiscretion.

Though Winterbottom forgoes the partially improvised approach of such recent efforts as In This World and 9 Songs, he does render Tristram Shandy as ramshackle as possible. The humor encompasses battle re-enactors, Al Pacino impressions, and physical gags focused on groins.

Indeed, as the script unravels—however intentionally—it also loses its connection to its source. The first half of the film maintains a superb balance between the novel’s japes and contemporary chuckles, although not without a certain predictability. (Anyone who’s read at least part of the novel won’t be surprised to see its famous black page become a black screen.) But then Sterne recedes and “Coogan” advances, and the movie begins to resemble a series of commonplace TV skits.

TRISTRAM SHANDY: A COCK & BULL STORY ( * * *)

Directed by Michael Winterbottom. Starring Steve Coogan, Rob Brydon and Keeley Hawes. • (R, 91 min.) • At the Osio Cinemas.