The first encounter between Sebastian and Mia is not auspicious. What happens before that, however, is  startling.

Traffic has jammed to a standstill on a freeway overpass in Los Angeles. Suddenly music bursts out of nowhere and drivers and passengers begin singing, and then climbing out of their vehicles and dancing. The sequence opens La La Land and establishes the tone of a musical fantasy that is, occasionally, grounded in the realities of modern-day life in a big American city.

Sebastian (Ryan Gosling) and Mia (Emma Stone) are typical of many young people who move to Los Angeles in search of artistic opportunities. Sebastian is a piano player who loves traditional jazz music; Mia is an actress who loves performing for other people.

They appear to be a natural fit, and so their slowly-blooming relationship plays out as a pre-ordained romance. But ‘happily ever after’ is an elusive concept to achieve, whether on screen or not, and Sebastian and Mia face many challenges to their prospects as a couple.

Damien Chazelle (Whiplash) wrote and directed. His original screenplay creates variations on the “driven musician” and “ambitious actress” stereotypes that are then fully realized in the performances by Gosling and Stone. They display a wonderful chemistry, aided, no doubt, by their previous work together. While they don’t exactly sizzle with erotic heat, they emanate friendly, compatible vibes. It makes it much easier to accept and embrace their relationship, which is better constructed to endure obstacles than most on-screen romances.

The musical sequences freshen up the familiar narrative of a bittersweet romance, interrupting and commenting upon the characters and their dreams, hopes, and disappointments. As with many movie musicals, only one song really pops: “City of Stars,” a lovely, wispy, catchy thing that allows Gosling and Stone a proper duet. The other songs, all composed by Justin Hurwitz (music) and Benji Pasek and Justin Paul (lyrics), are serviceable; neither Gosling nor Stone are powerhouse vocalists, but the songs fit their range.

More notable than the songs themselves, the musical sequences are set in iconic Los Angeles settings that add additional layers of commentary. Even if you’ve never set foot in the city, for example, the familiar environs of the Griffith Observatory invite dreamy feelings of nostalgia and yearning, and Chazelle and company expand upon and deepen a shared memory.

At times, the broad strokes of La La Land resemble a tourist’s map of Hollywood in structure and outline. While not especially authentic to the trials and troubles of aspiring entertainers, it’s cheery and chipper and colorful, perhaps to the point of curing the common cold.

The film opens in Dallas theaters on Friday, December 16.