1926: The Vitaphone sound-on-film process is announced by Warner Bros. studio. It’s the death knell for the age of silent films.
Vitaphone was prone to human error, since the alignment of the film projector and attached phonograph had to be precise even though it was set by hand. Nevertheless, it represented a marked improvement over previous sound-on-disc technologies.
Link. For more about Vitaphone, be sure to check out this diagram from widescreenmuseum.com. For more about early film sound, check out this article, via filmsound.org.