Which is to say, cinema pioneers moonlighting as famous composers.
Johann Sebastian Bach (Vladimir Gardin) gets Anton Ivanovich Voronov (Nikolai Konovalov) to lighten up in director Aleksandr Ivanovsky's popular 1941 musical Anton Ivanovich Is Angry. Voronov, a conservatory professor, is horrified that his daughter has decided to abandon classical music for a career in operetta; Bach steps down from a portrait in Voronov's studio to be a pragmatic voice of reason. (The film enjoys a rather nice score by Dmitry Kabalevsky.)
Gardin was a theatrical actor who jumped into the movies early on, producing, directing, and starring in silent-film versions of Russian classics. After the Bolshevik Revolution, he founded the State Institute for Cinematography (known by its Russian-language acronym, VGIK), one of the first film schools in the world. His 1923 film A Spectre Haunts Europe, an adaptation of Edgar Allan Poe's "The Masque of the Red Death" that played up confluences with the October Revolution, featured a scene of a massacre shot on the Odessa Steps that almost certainly gave Sergei Eisenstein the idea of using the same location for the massacre in Battleship Potemkin.
Ludwig van Beethoven (Erich von Stroheim) tickles the ivories for a gathering of nobility in Sacha Guitry's star-studded 1955 Napoléon. After finishing the "Appassionata," Beethoven then begins to play a bit of the "Eroica" symphony, prompting the Austrian archduchess Marie Louise (Maria Schell) to throw an anti-Napoléon tantrum—which, of course, is when Francis II decides to tell her that her marriage to Napoléon has just been arranged. Napoléon has a grand but oddly Les-Six-esque score by Jean Francaix; appropriate, though, since the whole story is being told in flashback by the supremely, cynically bemused Talleyrand (Guitry himself).
Stroheim, despite only directing a handful of movies (and being studio-replaced on a handful of others), was one of the greatest filmmakers of the silent era, with his crazy-lurid Foolish Wives, his brittle, elegant version of The Merry Widow, and his masterpiece, the partially lost but unparalleled Greed. His later acting roles (Grand Illusion, Sunset Boulevard) fixed his image—a deadpan-stiff Austrian gravity. Napoléon was his last screen appearance.