CBS will devote two hours to “48 Hours” this Saturday, rather than just the usual 60 minutes – the latest example of the series stretching beyond its usual structure.

The venerable newsmagazine, which has been on the air since 1988, will unveil an un-narrated film entitled “The Whole Gritty City,” which will follow three New Orleans marching band directors who prepare students to march in Mardi Gras parades as a means of keeping them safe from a city with one of the highest murder rates in the nation. Introduced by Wynton Marsalis, a CBS News contributor, the show will play start at 9 p.m. eastern, and is one of a series of interesting steps “48 Hours,” best known for exploring vivid murders, has taken in recent weeks.

“I feel we’ve earned the right to expand the base a little bit,” said Susan Zirinsky, senior executive producer of the show, who stressed that “48 Hours” is not veering away from its primary focus. “I don’t do this every week, but two or three times a year, I feel there are projects that can touch people in a way that has profound impact,” said Zirinsky, a CBS veteran who also helms breaking-news specials for CBS News and CBS Entertainment. “I’m always a crime and justice show, but mostly I’m about murder.”

Even so, “48 Hours” has pushed its envelope in recent weeks. In January, it presented a report on international adoptions gone awry led by correspondent Maureen Maher. The episode contained not the barest whiff of murder. And in October, “48 Hours” broadcast a story about the July, 2011, murder of Wayland, Mass., teenager Lauren Astley by her boyfriend, and used the crime to place a lens on the issue of so-called “breakup violence.”

The genesis of “Gritty City” comes from six years of work by Richard Barber, a special editor at the show who has leeway to pursue his own projects. In the process of working on a “48 Hours” episode that centered on a murder in the Big Easy, Barber came upon the story of the kids and the bandleaders and decided to devote time to the project.

“He was so taken with music and the kids and he thought this would make a great documentary,” explained Zirinsky. “He would take time off and shoot it on his own. We kind of contributed ‘consigliore’ advice and counsel. He raised money through grants and Kickstarter.”

CBS News has acquired the rights to show Barber’s documentary, which was shot in New Orleans between 2007 and 2010, and produced along with Andre Lambertson, a cinematographer and photojournalist who has taken an interest in spotlighting children dealing with poverty and violence.

Zirinsky hopes the two-hour special program will offer counterprogramming to Olympics coverage on the various networks owned by NBCUniversal. And she hopes to steadily find more audience on Saturday nights, which the broadcast networks largely populate with repeats, some sports and movies. “More people are staying home and going out later,” she said, and the program’s focus on crime-and-justice stories and original, shoe-leather reportage, carries some appeal.

Any more excursions planned to different subjects? Zirinsky said she is open to ideas from her staffers. “The creativity and power of people I work with allows me to take chances and push the envelope.”