In the era of silent film it was common to have live piano or organ accompanying the show. In Japan, they had people as well – specially trained to provide narration, translation, poetry, and commentary for the films on the screen.
This ties into the Japanese theatre traditions of Noh and Kabuki, who also had narrators or a chorus to achieve the same goal. The benshi were immensely popular, even celebrities in their own right. You might go to a specific theatre just because of the benshi performing there.
The practice mostly died out with the introduction of sound in film. The practice is having a bit of a revival now under the name Neo-Benshi.