In 1931, four years after “The Jazz Singer” had popularized synchronized sound and only two years after “The Broadway Melody” won the best picture Academy Award, the movie musical was considered a dead duck at the box office. MGM was so distraught at the public’s indifference that it halted production on its most lavish revue, “The March of Time.” The audience had soured on those long, plotless, self-important diversions that tended to show off a studio’s players as stilted and insincere.The dance numbers looked silly, arrayed on a proscenium arch, and songs sounded a lot better on radio – better songs, better singers, better sound.

Two movies changed all that – and ushered in a golden decade of inventive, sexy, funny, irreverent musicals that, at their best, managed the neat trick of offering intoxicating escapism while nailing the class consciousness and class fantasies rife during the Depression. The first was Frank Tuttle’s “The Big Broadcast” (1932), an homage to France’s innovative director, Rene Clair,that used surreal camera tricks and animation. Its commercial draw was a variety of radio singers and signature songs; a public already enchanted by their voices lined up to see their faces.That Paramount film was popular enough to spawn a series, yet eventually disappeared.

The second was Warner Brothers’ “42nd Street,” which followed a few months later, in 1933, and had an altogether different history. Nominally directed by Lloyd Bacon with a strange cast – one star (Warner Baxter), two untested juveniles (Dick Powell and Ruby Keeler), and a fleet of character actors – and new score, it vivified the musty cliches of backstage musicals urgently enough to sustain its story, then exploded with climactic choreography that made the camera the star.It abandoned the stage for pinwheels and kaleidoscopes,zooming or overhead shots, mini-dramas fraught with sex and violence, all underscored by the fairly nov el idea that this is a movie: Stages? We don’t need no stinkin’ stages.

The choreographer was a 37-year-old, womanizing, alcoholic Broadway veteran with the memorable nickname Busby. He soon became king of the Warner soundstage, a swashbuckler of the giant crane, the commander of a legion of alabaster-skinned casting-couch beauties who didn’t necessarily require any talent beyond finding their marks and smiling on cue. A Busby Berkeley movie was an idiom unto itself. Audiences happily whiled away the moments with Ruby Keeler’s adorably clumsy dancing and Dick Powell’s already dated tenor (and high-rise pompadour), along with barking Ned Sparks, flustered Guy Kibbee, flustering Hugh Herbert, and the rest, waiting for the outlandish dance numbers, usually saved for the end.

There comes a point in the rediscovery of every generation’s sexual expression when double entendre loses its doubleness. At that point, we are left to marvel at how really perverse our parents or grandparents were. Forget about swimming through dozens of openscissor female legs or male voyeurs arrayed on their tummies shaking their heads or other obvious indications of omnivorous, ambidextrous, and neutered sexuality: What is going on with all those midgets and diapers and spanking? Just as there is no non-biblical evidence to corroborate Exodus, the historical record fails to support the idea, advanced by “42nd Street,” that American men ever referred to their trousers as “panties.”

As Berkeley became more confident, so did the sexuality of his stars – including such antidotes to Keeler’s doe eyes as the hot-blooded sarcasm of Ginger Rogers and the hot-blooded everything of the great Joan Blondell, whose right mammary makes a magnificent entrance in “Dames.” In real life, she married Powell, which certainly makes him more interesting in retrospect. In “Footlight Parade,” Berkeley found a perfect (though one-time-only) double in James Cagney, as a dancer-choreographer whose mile-a-minute charm ratchets up the romantic urgency in a film too long on build-up, but ready to deliver with “Shanghai Lil.”

Berkeley’s rapid decline in the late 1930s (notwithstanding his inspired salute to phalluses and decapitated heads in 1943’s “The Gang’s All Here”) is usually attributed to his personal failings. More likely, the next generation simply cringed in embarrassment.

It took a more removed generation to rediscover him – the postwar baby boomers, who may have found Busby incomprehensible during childhood TV infusions but, eventually, figured him out with the help of natural herbs and hallucinogens. The transformation of “42nd Street” into a 1970s Broadway extravaganza defanged him once and for all. Or not. A myth that clings relentlessly to these films, endlessly iterated in talking-heads featurettes, defines them as mindless or mind-blowing entertainments; respites from the woes of the Depression. In fact, the musical numbers brim over with reminders, sometimes ironic (Ginger Rogers in a necklace of giant gold coins singing, “We’re in the Money,” when no one was), sometimes angry (bonus marchers restored to dignity in “Remember My Forgotten Man”). The stories are strictly “let’s put on a show,” but the musical numbers underscore the misery behind the melodrama and farce.

For that, Berkeley can take only part of the credit. Warner Brothers has collected five films and a bonus disc as “The Busby Berkeley Collection,” but it could just have legitimately released them as “The Harry Warren-Al Dubin Collection.” They are the forgotten men in this series, though it is impossible to overstate the importance of their songs. Berkeley’s style and, for that matter, the musical conventions of the 1930s required taking a song and playing it over and over again for the duration of a choreographed number. In later years, musical direc tors would allow arrangers to “open up” songs, extending them with variations and interludes. But in the Warner musicals, those songs had to hold their own.

Warren uses triplets, for example, to inject a happy spirit (“I don’t know if it’s cloudy or bright”) or a dour one (“remember my forgotten man”), and routinely combines eighth notes, dotted eighths, and 16th notes to create rhythmic ripples in most of his songs in this period (“I must have you every day / As regularly as coffee or tea). “You’re Getting To Be a Habit With Me” is a splendid example of two contrary melodies alternating in a song.

Dubin, the man who rhymed “scanties” and “panties,” caught the mood of the project exactly with lyrics like “ev’ry kiss, ev’ry hug seems to act just like a drug,” or with the relentlessly mooing “you,” every three bars throughout “Shadow Waltz.” He and Warren were never more masterly than in “Lullaby of Broadway” (“Gold Diggers of 1935”), countering the main strain’s mellow swing with a whole-notes passage, “Gooood niiiight, baaay-beeee.” These songs are based on melodic hooks that circle back on each other, allowing Berkeley to go for broke without wearing out their welcome.

Warner Brothers DVDs are justly renowned for treating studio archives with the care that Criterion puts into its international collection of classic films. “The Busby Berkeley Collection” is exceptional, even so: cause for spelunkers of obscure popular cultural to cheer. It includes smashing prints of “42nd Street,” “Gold Diggers of 1933,” “Footlight Parade,” “Dames,” “Gold Diggers of 1935,” and a 21-number anthology,originally prepared for laser disc, which isolates celebrated numbers and adds excerpts from four other 1930s Berkeley pictures, including “Wonder Bar” – though not the infamous blackface fantasy,”Goin’ to Heaven on a Mule,” which is now considered too insensitive even for history. But that’s just the main course.

A savvy selection of short subjects and cartoons fills out each disc with rare opportunities to see the brilliant bandleader Don Redman, who almost single-handedly codified big band jazz orchestration, 7-year-old Sammy Davis Jr., the neglected songwriter-performer Harry Barris and his wife, Loyce Whiteman, an Adam and Eve parody with June MacCloy and Leon Errol, Harry Warren, and many vaudevillians – quite a treasure.

Mr. Giddins’s column appears every second Tuesday in The New York Sun.