Film It’s 1907 and here’s singer Jean Noté performing the French national anthem with synchronous sound. The Jazz Singer’s generally thought of as being the first sound film, and although it’s true that it was the first to utilise a technique which was commercial repeatable, the director Georges Mendel achieving a similar effect over a decade earlier. One can well imagine if this was shown in cinemas, the audience taking to their feet and singing along. Just remarkable.
But this still isn't the earliest. William Dickson was experimenting with sound in the mid-late 1890s.