This clip is pulled from footage taken at the 1939 New York World's Fair.  It shows people dancing to music played by Glenn Gray and his orchestra.

I believe this clip demonstrates the various forms of Foxtrot that were danced during that era.  I am struck by how the dances appear to resemble not only Foxtrot, but Quickstep and Argentine Tango as danced today.

There's no sound on this footage, so we don't know what music was being played.  However, since we clearly see couples doing the Jitterbug, we can assume it was some sort of medium to fast swing number.