James Franco’s exuberant directing effort “The Disaster Artist” is a love letter to bad moviemaking — and how much you can embrace that kind of badness may determine how much you’ll enjoy his efforts.

That’s not to say “The Disaster Artist” is a bad movie. Far from it. It’s smart and funny and knowing, and is propelled by a strong cast led by Franco himself and his brother Dave as a hapless duo making what future generations will call the worst movie of the 21st century, “The Room.”

It’s 2002 and fledgling actor Greg Sestero (Dave Franco) is in bad shape. He desperately wants to be an actor, but he’s too timid and quiet to make an impression on his acting teacher (Melanie Griffith, in a nicely offbeat cameo). Another student in the class, played by James Franco, has no such problem, as he dives into a climb-the-walls rendition of Stanley Kowalski’s big scene from “A Streetcar Named Desire.” Greg decides he needs some of the mojo this classmate, Tommy Wiseau, can rub off on him.

Greg and Tommy become fast friends, even though there’s a lot about Tommy that Greg can never figure out. For starters, there’s his place of origin — he says he’s from New Orleans, but his accent and his mangled English (he’s only passingly familiar with the word “the”) suggest somewhere in Eastern Europe. Then there’s his money, which seems to be abundant but coming from no apparent source.

Tommy and Greg leave San Francisco for Hollywood to pursue their acting dreams, with different results. Greg lands an agent (Sharon Stone) almost immediately, while Tommy rejects casting directors’ attempts to put him in villain roles. After an embarrassing attempt to audition for a producer (Judd Apatow) in a restaurant, Tommy decides he must pave his own road to stardom.

He starts writing his movie script, buying equipment and renting studio space to make his movie, “The Room.” He takes for himself the starring role, Johnny, an all-American nice guy with a shrewish girlfriend, Lisa — and gives Greg the role of Mark, Johnny’s best friend, who betrays Johnny by succumbing to Lisa’s come-ons.

Tommy hires a crew — including a script supervisor, Sandy (Seth Rogen), and a cinematographer, Raphael (Paul Scheer) — and he and Greg audition actors. James Franco deploys a better cast than Tommy ever had, including Ari Graynor as Juliette, the actress who played Lisa, as well as Zac Efron, Josh Hutcherson, June Diane Raphael and Jacki Weaver.

Director Franco, working off a script that the team of Scott Neustadter and Michael H. Weber (“The Fault in Our Stars”) adapted from Sestero’s memoir, is relentless in not giving his character any sentimental cover. Franco gives a powerhouse performance by depicting Tommy as an inept braggart, barking orders to the crew and being abusive toward Juliette while filming an atrocious sex scene. Tommy’s mean streak comes out strongest when he grows jealous of Greg’s comparative success and of Greg’s girlfriend, Amber (Alison Brie, Dave Franco’s real-life wife).

Franco concludes “The Disaster Artist” with a series of split-screens, showing his cast’s re-creations of scenes from “The Room” alongside the originals. The comparison is a subtle masterclass in acting, showing the difference between bad actors floundering through a scene and good actors trying faithfully to copy the same moves. It also puts the lie to Wiseau’s self-mythologizing “I meant to do that” revisionism that Franco seems to endorse.

Watching “The Room,” even with an audience hooting at every amateurish move, it’s staggeringly difficult to see it as anything other than a sad, pathetic film made by someone oblivious to his lack of talent. The ultimate flaw of “The Disaster Artist” is that it fondly celebrates a movie that isn’t worth celebrating.

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The Disaster Artist

James Franco stars and directs this loving look at amateur filmmakers who stumbled into creating a cult favorite.

Where • Area theaters.

When • Opens Friday, Dec. 8.

Rated • R for language throughout and some sexuality/nudity.

Running time • 103 minutes.