Short answers, pulled from the story.
A live pianist accompanied the first film screened by the Lumière brothers in 1895. The music was not an artistic vision but a technical necessity to drown out the deafening mechanical noise of the projector.
The Oz Film Manufacturing Company began sending full-length scores by Louis F. Gottschalk by 1914. This development marked a shift where music became a narrative force rather than just background noise.
Erik Satie created what is considered the first frame-by-frame synchronous score for René Clair's Entr'acte in 1924. This work utilized a flexible, aleatoric score that varied in tempo to match the inconsistencies of early projection speeds.
Max Steiner composed the landmark score for King Kong in 1933. This score created a precise synchronization between image and sound that had previously been impossible.
The Society for the Preservation of Film Music was formed in 1983. This organization works to preserve music manuscripts and studio recordings that might otherwise be discarded by movie studios.
De Wolfe Music set up the first production music library in 1927. This library provided music to various film, TV, and commercial projects for a fee on a work for hire basis.