Sound film
The primary steps in the commercialization of sound cinema were taken in the mid- to late 1920s. At first, the sound films which included synchronized dialogue, known as "talking pictures", or "talkies", were exclusively shorts. The earliest feature-length movies with recorded sound included only music and effects. The first feature film originally presented as a talkie was "The Jazz Singer", released in October 1927. A major hit, it was made with Vitaphone, which was at the time the leading brand of sound-on-disc technology. Sound-on-film, however, would soon become the standard for talking pictures.
André Charlin
Charlin became involved in cinematography at a time when sound was starting to be added to motion pictures, and began to build equipment for synchronous sound playback.
At first this used 33 rpm records.
The first "talkies" appeared in 1931, and Charlin began working on ways to improve sound quality through better recording technology.
He founded a recording studio in 1933 that produced the sound tracks for many prewar movies, including in 1934 a stereo sound track for Abel Gance's 1927 silent movie "Napoléon".
He moved into techniques for film projection with a 1935 patent for "Cyclope" focussing and a 1938 patent for "Actua Colour" to project colour films which was used in over 1,000 movie theatres by 1948. 
During World War II he turned to making dynamos to power the lamps of bicycles.
In 1949 Charlin stopped producing cinema equipment and sold all his related patents to Philips of the Netherlands.
Early in the 1950s Radio-Cinema, a subsidiary of the Compagnie générale de la télégraphie sans fil, acquired Charlin' company.