Higher Frame Rates

VHS at 50 and 60 frames per second... how is this possible?

Analogue video is interlaced, there are two fields per frame which works well for CRT screens. If you split the fields into their own frames you can get smoother motion on digital displays.

Not everything needs to be processed this way or even deinterlaced at all. If it was recorded on film it will usually be 24 frames per second and so both fields would have the same information.

This rally test video was grabbed at lossless quality and then deinterlaced. It was increased in size so that YouTube will play it at 50fps.
Grabbing and deinterlacing is all done in VirtualDub2
Grabbed at 768x576 25fps
Deinterlaced 768x576 50fps

This test video of the 1984 John Martin's Christmas Pageant was copied to DVD then deinterlaced based on the DVD rip using Python and ImageMagick and upscaled to 1080p.
The full video in 30fps is at https://www.youtube.com/watch?v=ITNelbJIy6Y&t=900

Please note that YouTube does compress the video significantly and so the quality seen is much lower than the original.
YouTube will downscale 576p video to 480p25 so upscaling to 720 lines will keep higher frame rates.