‘La La Land,” Damien Chazelle’s exuberant, thoughtful ode to bygone movie musicals, begins with two bravura gestures. After a retro-looking CinemaScope logo announcing the film’s big-screen purists’ credentials, it opens in earnest with an exhilarating, wildly ambitious production number during which dozens of Los Angeles strivers sing and dance atop their cars during a highway traffic jam.

Bright, primary-hued and boldly staged as if to occur in one unbroken shot, that prologue sets the stage for what’s to come: a nostalgic boy-meets-girl romance shot through with winsome musical numbers and modestly charming dance numbers that, at its core, makes a dazzling case for movies as they used to be. With “La La Land,” Chazelle seems to be staking his claim, not only as a passionate preserver of cinema’s most cherished genres (he made his mark a few years ago with his breakthrough drama “Whiplash”), but also a savior of the medium itself.

An ambitious production number takes place during a Los Angeles traffic jam. (Dale Robinette/Lionsgate)

It’s during that traffic jam scene that the principle players meet cute, as they say in the trade. Mia (Emma Stone) is a young, mostly out-of-work actress making a living as a barista on a studio back lot. Sebastian (Ryan Gosling) is a jazz pianist with exacting standards and a somewhat sour outlook on love. According to formula, when they first encounter one another sparks fly, but they’re argumentative and full of aggression. As their relationship develops, it becomes a vessel for all manner of arguments about art, ambition, ideals and compromise, winding up in a place that, even if some viewers see it coming, will almost assuredly leave several of them in a cathartic puddle. (To those looking to “La La Land” as a lighthearted antidote to the heaviness of this season’s movies, a gentle warning: There won’t be sobs, but there will be tears.)

Emma Stone as aspiring actress Mia. (Dale Robinette/Lionsgate)

Ryan Gosling as jazz pianist Sebastian. (Dale Robinette/Lionsgate)

Working together for the third time, Stone and Gosling quickly establish an easy rapport with one another, their surpassingly attractive physical features the perfect foils for Chazelle’s aesthetic approach of naturalism and extreme stylization. Neither is a particularly gifted singer or dancer, but that hardly matters in a film that sweeps them up as if carried by a swirling force of nature: They have the unforced grace of natural performers, lending an offhand rakishness to every step they take. In addition to being fine actors in their own right, their gifts dovetail perfectly with composer Justin Hurwitz’s ingenious songs, and have been lent even more sparkle by Tom Cross’s crisp editing — which stays gratifyingly quiet during the gracefully filmed dance sequences.

One of the movie’s themes is the often absurd pursuit of stardom that defines Los Angeles at its most shallow and careerist. Chazelle lards his script with little digs at showbiz jargon. (A young screenwriter Mia meets proudly announces his “knack for world-building.”) The film is literally inscribed with Hollywood’s mythic past, from such familiar backdrops as the Griffith Observatory to the movie star murals on the city’s streets. The subtext is that it has two stars at its center who can convey hunger and avidity at one moment and a shiny sense of preordained fame and fortune the next.

From the director of "Whiplash," this movie-musical stars Emma Stone and Ryan Gosling, who fall in love while trying to make it in Los Angeles. In this trailer, Gosling sings the melancholy "City of Stars." (  / Lionsgate)

But the real star in “La La Land” is the movie itself, which pulses and glows like a living thing in its own right, as if the MGM musicals of the “Singin’ in the Rain” era had a love child with the more abstract confections of Jacques Demy, creating a new kind of knowing, self-aware genre that rewards the audience with all the indulgences they crave — beautiful sets and costumes, fanciful staging and choreography, witty songs, escapist wish-fulfillment — while commenting on them from the sidelines.

In Chazelle’s case, that commentary isn’t ironic: It isn’t delivered with pompous eye-rolls or scare quotes. Instead, he harbors a genuine loving concern for a cinema that, in an age dominated by comic-book spectacles and stories dumbed down and miniaturized to fit an iPhone, is on the verge of losing the scale and sweep and narrative values that defined and distinguished it in the first place.

Throughout “La La Land,” Gosling’s character bemoans the state of jazz as a bastardized art form, further sullied by an audience indifferent to quality, originality and virtuosity. It’s difficult not to hear the filmmaker himself in those words, anxiously observing how the art form he first fell in love with is undergoing existential transformation. In “La La Land,” his answer is clear: The best way to deal with something that is shifting and changing under your feet — whether it’s love, life or art — is to just keep dancing.

PG-13. At area theaters. Contains some obscenity. 128 minutes.