With thousands of musicians performing all over the city on a warm St. Patrick’s Day afternoon, it felt fitting that Emmett Malloy’s documentary "Big Easy Express" closed SXSW Film at the Paramount Theatre.

Hundreds of fans lined up more than an hour before the 4 p.m. screening to catch the documentary that followed Mumford and Sons, Edward Sharpe and the Magnetic Zeroes and Old Crow Medicine Show on a train from the Bay Area to New Orleans. Fans of the bands had packed the grand, old theatre to the rafters by the time to the film started.

A long tracking shot introduces the audience to the three bands jamming in separate cars, as the silver California Zephyr train cruises through the western part of the United States. Rolling hills and flat prairies seen through train windows flip by like Instagram photos in an album. The bands decided to join forces on the train, we are told in voiceover, in order to reconnect with the land and each other, to lift themselves back into the magic of a simpler time. Another musician adds that it is a "tour of dreams." And much of the film is shot and told in a sort of dreamlike style, the loose narrative structure hinging on the ride to New Orleans and a decent amount of concert footage. The film never probed too deeply into the reasoning behind the tour or the musicians’ inspiration or personal connection to the music they played. Instead their playing did the talking.

Shaky hand-heled cameras capture concert footage, often in black and white, as the camera unsteadily zooms in and out, panning to the audience. The concert footage often features music not synced with the slow-motion movement of crowd or musicians, giving the movie the feeling of a music video that delivers more an abstract emotional portrait of the event and less a realistic portrayal of the events.

Nonetheless, the performances — both those on stage and the many improvised jam sessions on the cramped train — are all imbued with a deep sense of joy and purpose. The audience at the Paramount Saturday responded as if they were at a concert, applauding after solos and at the end of truncated songs. Many probably were in attendance at the concert held in East Austin, as evidenced by the approving and nostalgic cries from the audience. The highlight of the Austin show, outside of the memorable cloud-head that formed that day and ended up on countless Facebook pages and Twitter feeds, was the inclusion of the Austin High marching band. Cameras followed members of Mumford and Sons as they traveled to the school for some exercise and rehearsal with the starry-eyed high schoolers. As with all of the bands in the film and the teaming crowds at each of the sold out shows, the Austin High students and members of Mumford and Sons formed an immediate and unspoken bond around their one common love - music.

Following the screening, Malloy and members of each of the three bands briefly took part in a Q&A before the bands took the stage for a 45-minute concert on the Paramount stage. With their biggest hits having appeared in the film, Marcus Mumford decided to open the set with plaintive new tune, "Where Are You Now?" Members of Old Crow Medicine Show and the massive Magnetic Zeroes crew joined for a few group tunes, before ceding the stage to Edward Sharpe’s band. All of the musicians convened to close the evening with a raucous sing-along to "This Train" before the doors opened and the audience streamed out into the street for — what else? — more music.