The special projector that was used for projection of sound movies on
TV had a special shutter that would scan alternate frames 2 and 3 times.
This created 60 video frames per second.  I used to have such a video
projector made by the Holmes Company.  It had formerly been used in one
of the area TV stations.

Remember however, that this applies to sound films which, as you
correctly noted, are run at 24 frames per second.  Silent films run
slower and thus when you see them being run on TV they are being run
about 50% faster than they should, therefore all the action looks
artificially speeded up.  I believe that most, if not all, TV stations
now use an electronic scanning device to convert sound movies to video
format.

Hal Davis