(The action starts at 1:46 in the video)
This ‘St Louis Blues’ scene from 1944 may be a portion of one of his band’s short films. The ‘guitrobot’ is named ‘Stringy’. What a hoot!
While vocoders already existed at that time, they were the size of refrigerators (and used to encode top-secret comms between Washington and London). They had to wait for transistors and integrated circuits to become pop tech.