I saw this film in the 90's, it was a hybrid live action and cartoon (manga style) set after a nuclear (atomic?) war.
The part that sticks in my head from the live action part was the hero (coming out after the bombs, in his radiation suit) finding a piano on a beach/rubble ground and playing a short tune on it. This melody recurred through the film.
In the cartoon part, there were Victorian style buildings and people, with flying whales going overhead.
I think a girl would turn up in the live action part & that triggered the switch to the cartoon parts, and she was then a character in that part of the story.
For some reason, I think this film was Australian in origin.