As the poster here says, the film, directed by Bruno Bozetto, is a parody of Fantasia in that it contains animated sequences set to music. But rather than attain high art like the Disney classic, Allegro goes more low-brow, humorous, and cynical (aside from the tear-jerker Valse Triste sequence). Between each animated piece are these hilarious skits about the production of the pieces pertaining to the brutal conductor, the orchestra of old ladies, the enslaved animator, and a random gorilla. The film really captures the spirit of filmmaking in the 70s: a lot more zany and free-form than any other decade. If nothing else, find the Ravel's Bolero sequence on Youtube. It is absolutely brilliant and marvelous to watch. For now, here is the trailer for the DVD release.
The "director" (not the film's actual director) at the beginning explains that he's never heard of this "Pisney" or "Bisney" guy who claims to have done this concept first.