If you've seen the early demonstration movie of Witt & Berg performing four songs, here's a very interesting short. In it, you have a view of the stage and camera from the side; Edward B.. Craft, Executive Vice-President of Bell Labs explains we are about to see a recording; an assistant director blows a whistle, and you see the entire operation: the artists to the side performing, and in the center, the camera in its sound-proof booth.
This was made as a demonstration movie, intended to sell the Warner Brothers and their theater managers on what would become the Vitaphone system. It probably sat in the Warners archives for three quarters of a century before anyone decided to do anything with it. It's a fine movie watch for those interested in not only early movies, but early move-making!