This is a song from the first movie (or the 3rd episode taken from that movie) of the popular italian cartoon Signor Rossi. But it is not just this song or episode but the whole show that is full of trippy animations and imagery.
This animation for Jean Sibelius’ Valse Triste is an excerpt from the movie Allegro Non Troppo (1976) by Bruno Bozzetto.
[I planned to post the animation Bozzetto created for Ravel’s Bolero (you can watch it here), but was not able embed a decent version here. Many thanks to Roland for sending me the link to the Bolero animation!]