AUSTIN, Texas (AP) ― Stars of all stripes and celebrity hit town to close out South By Southwest, but it was a marching band that stole the show Saturday.

Members of the Austin High band watched their star turn in the premiere of filmmaker Emmett Malloy’s “Big Easy Express,’’ then joined documentary subjects Mumford & Sons, Edward Sharpe and The Magnetic Zeroes and Old Crow Medicine Show in an outdoor concert at the University of Texas as the music conference fell into an exhausted heap on its final night.

Across town, Timbaland held a listening party at Perez Hilton’s annual to-do. Norah Jones played her new album for an appreciative group of fans. Matthew McConaughey joined The Cult during a free concert. Punk rock icon Bob Mould played “Copper Blue’’ in its entirety, bringing out the graybeards. And Peter Buck and Mike Mills of R.E.M. joined The Posies and Blitzen Trapper in one final tribute to Big Star frontman Alex Chilton, who passed away two years ago as he was due to participate in SXSW.

Rumors of celebrity appearances swirled up and down Sixth Street, but few of them materialized as St. Patrick’s Day revelers clogged downtown Austin in a frenzy of partying that didn’t end until 2 a.m. last call.

Superstars such as Bruce Springsteen, Jay-Z, Eminem and others made this the busiest SXSW ever, overflowing with celebrity, secret performances and high-dollar endorsements that made sure the festival looked nothing like the humble event that started 25 years ago with just 200 bands spread over 12 clubs. With so much going on and plenty of places to get hammered on green beer, even the usually most exclusive events were easy to get into.

It took a bumpin’ tuba line and a bunch of enthusiastic high school kids to shake off the glitzy veneer that had many longtime festival participants grumbling about the good old days and inject a little innocent joy back into the conference.

With the UT Tower lit up in the background, the band took the stage, then laid down a rolling groove before joining Mumford & Sons on “The Cave,’’ recreating a powerful moment from “Big Easy Express’’ in front of thousands of fans on the lawn at the Lyndon Baines Johnson Presidential Library.

“That’s real music, ladies and gentlemen,’’ Marcus Mumford told the crowd after the song. “That’s real music from real people.’’

Afterwards fans surrounded marching band members on the street and chanted: “One more song! One more song!’’

The love of making music and the community brought by close collaboration were the dominant themes of “Big Easy Express,’’ which made its world premiere earlier in the day at the Paramount Theatre, then was replayed for the crowd before the night’s concert.

Malloy follows the three bands as they made a train trip from California to New Orleans via Austin. They covered 4,000 kilometers in a week and a half, playing music almost every step of the way and enlisting Austin High to join the fun in one of the film’s most delightful moments.