A rousing, impassioned study of the challenges and rewards of peace activism in Cuba, “13 Million Voices” might best be described as a finished film about a work in progress: Cuban-American political relations have shifted so much during, and even since, the production of Janelle Gueits’s documentary that it could come to be most valuable as a kind of intermediate marker of present-tense history. Shot over the course of a decade, often raggedly on the fly in what the filmmaker refers to as “guerrilla” fashion, the film centers on the 2009 Peace Without Borders concert in Havana’s aptly named Revolution Square — but weaves a number of preceding and subsequent social narratives into its arms-aloft, future-minded celebration.

Well-traveled on the documentary festival circuit, “13 Million Voices” will enjoy limited theatrical exposure — but is best tailored to on-demand platforms where, with any luck, the population whose story it most directly tells will be able to access it. The eponymous figure, incidentally, refers to the 11 million residents of Cuba, in addition to two million Cubans living in the U.S.

Herself a Miami-based Cuban-American, Gueits began the film to document her own role in planning and producing an awareness-raising concert in Cuba with the youth-oriented nonprofit Roots of Hope — a goal that eventually converged with that of Colombian pop superstar Juanes, who had already headlined the inaugural Peace Without Borders concert the previous year in his homeland. Its Cuban sequel, a blockbuster six-hour assembly of top Latin artists intended to communicate direct political motivation to a young, politician-averse crowd, drew over 1.3 million attendees on September 20, 2009 — among the largest ever concerts of its kind. (The film, wholly sympathetic to but not officially endorsed by the Peace Without Borders movement, alternatively terms it the largest event for peace in world history — a more elastic claim, but Gueits’ ebullience is understandable.)

Alternating between casual, off-the-cuff HD footage and more formalized talking-head material, Gueits traces the concert’s very gradual development with an insider’s immediacy, her camera capturing first-hand the multitude of logistical and political complications its organizers encountered along the way. (Tech credits throughout are deliberately low on polish and high on urgency.) Viewers will find this groundwork justified by a wealth of lively, bristling onstage and backstage footage from the big day. If the film is obviously indispensable for Juanes fans who never viewed the widely broadcast concert, even those unacquainted with his music should be compelled both by his stage presence and his outspoken involvement with the cause.

“13 Million Voices” is perhaps most affecting, however, when its gaze drifts from the limelight — or rather when it casts its own spotlight on less celebrated contributors. Interviews with local, previously disenfranchised youth activists and suppressed artists most charismatically, socially conscious rap duo Los Aldeanos, whose lyrics have met with government censorship — lend the film weight and conscience. The concert was for these people, after all; “13 Million Voices” sings loudest when it’s about them.