Theory of Obscurity: A Film About the Residents
Starring Matt Groening, Les Claypool, Penn Jillette, Jerry Harrison, Gary Panter, Robert Crow, Homer Flynn, Hardy Fox, Jay Clem, John Kennedy
It's a documentary and music movie, and has a rating of 7 out of 10 from Imdb which is usually fine for this kind of movie.
Watch it here
Not found streaming from Spain.