Cinema. Cannes Film Festival: From Alexandre Desplat to Bono, music is a very special guest.

A black, upright piano at the edge of the stage. Film music is playing to a sold-out crowd on this beautiful Sunday in Cannes, before a packed house of festival-goers hanging on the every word of a star composer. Alexandre Desplat creates a melody in D major on the keyboard, the one he composed for Jonathan Glazer's film Birth (2004). "It starts with the flutes because I'm a flautist. Then I play around with references, which I make my own. D major is a very open key."

This suspended moment isn't a concert, but a lesson. Nothing masterful or soothing: more of an allegro couch conversation, interspersed with film clips. At his side is Mexican director Guillermo del Toro, his accomplice and friend, with whom he's working on Frankenstein , their next film. Together, they unravel the thread of a career made of notes and images.

Alexandre Desplat comments on images, speaks, then returns to the keyboard, whistles, hums, and replays the gentle strangeness of the music from The Shape of Water (2017), which earned him one of his two Oscars. "Cinema allows me to slip into the film like an actor would."

A film buff, he evokes his adolescence in images, the films of Spielberg, Scorsese, and the music that accompanied them: "I went back to see films just to hear their music. I understood that anything was possible in cinema." For him, music doesn't illustrate, it accompanies the characters. As the third author, behind the director and the screenwriter, he writes "the musical voice that takes the film elsewhere."

From Robert Guédiguian's Ki lo sa? (1985) to The Grand Budapest Hotel , via Harry Potter and Twilight, Alexandre Desplat is the most popular film composer of his time. In the tradition of Jarre, Legrand, Lai and Delerue. He has won two Oscars, three Césars, two Baftas, two Golden Globes, two Grammy Awards, a Silver Bear... And yet, this Sunday at the Cannes Film Festival, humility is still playing a muted role.

The Cannes Film Festival understood it better than ever this year: without music, cinema would lose a part of its soul. The ^78th edition illustrates this on the big screen. It opened with a musical film, Partir un jour by Amélie Bonnin starring Juliette Armanet.

Starring in the documentary Bono: Stories of Surrender , directed by Andrew Dominik and presented at a special screening, the U2 legend electrified the Croisette with his prose and vocals. Festivalgoers, standing in the Grand Théâtre Lumière, gave this black-and-white autobiographical tale a standing ovation, like a concert in its own right. Screened in the Cannes Première section, Sebastián Lelio's La Ola enchanted with its take on the #MeToo movement as a stylized musical comedy.

SACEM is supporting this musical Cannes by programming live performances. On the beaches of the Croisette, the evenings feature DJs and musicians. A star since his performance at the opening ceremony of the Paris Paralympic Games, Lucky Love, the face of Magnum, delivered a fiery showcase. A trained actor, he sees his music videos and songs as short films: "When I write, I have images in my head. Music, for me, is inseparable from cinema." Present at Cannes last year for Yolande Zauberman's La Belle de Gaza , he dreams of collaborations with Xavier Dolan or the Boukerma brothers.