Beautiful film by Fernando Trueba, Javier Mariscal and Tono Errando :) This is part of the making of and shows one of my favourite shots, when Rita dances and turns in a 3d created environment to the rhythm of the piano played by Chico.
I find it interesting when Mariscal points out their use of clean lines shaping the characters' profile, with just the exact amount of lines to place an eye or the character's mouth, no creases and a single, plain colour with a simple shading to give volume.
In another video they mention something else I'd noticed in the film, that is the movements of the camera. By first shooting the scenes with real actors, they can give the animation that same effect of movement recorded by the camera, making it very appealing and realistic.