This is the first movement from Eine Kleine Nachtmusik (‘A Little Night Music’) by Mozart, composed in 1787. 

The work is also called ‘Serenade No. 13’, K525 in G major. It was written for strings. 

The drawings in the video illustrate the structure of the piece. It is in Sonata Form. 

The sections are called the  Exposition, the Development, the Recapitulation and the Coda. 

The man represents the first tune – called the first subject (SI).

The woman represents the second tune – called the second subject (SII).

The pink clothes refer to the tonic key. The blue clothes refer to the dominant key.