"Hot Chocolate" is a short film that is a 'Soundie'...an early sort of music video that was played on specially built jukeboxes from 1940-1947. These jukeboxers were unusual because they not only played music but video...like music videos of the modern era. And, if you are curious about this an other soundies, you might want to buy yourself a copy of "Soundies the Ultimate Collection"...a 4 disc set of about 200 of these films.
In this Soundie, Duke Ellington and His Orchestra play for a group called "Whitey's Lindy Hoppers". The Lindy Hop, by the way, was a dance much like the Jitterbug...very athletic and loved by the young (adults mostly saw this type of dancing as a sign of the coming apocalypse!). This Soundie is a bit unusual in that Basie credits one of his featured performers by name...folks you likely have never heard of and it might be one of the only times you can see and hear them.
The star of this one clearly are these amazing dancers. I doubt if I ever could have danced this well and this athletically and they are pretty amazing to watch....so much so that you barely notice the music!