Here's another of the forgotten three-minute sound shorts or "Tonfilms" produced in Germany from 1906 through 1910. They were exhibited in a dedicated theater in Berlin, but the difficulty of showing them properly made them obscure, so that by the time talking pictures arose again twenty years later, they had almost entirely been forgotten.
Unlike the others, the two singers do not enter and take up their position in the center of the stage. Instead, the camera discovers them, the woman on her balcony and the man just outside, whereupon they launch into the duet "Liebchen Komi In Mein Stubchen".