First, take a look at this 1895 short movie "L'Arrivée d'un Train Ã la Ciotat" ("Arrival of a Train at La Ciotat," from the Lumière Brothers. This film was upscaled to 4K and 60 frames per second using a variety of neural networks and other enhancement techniques. The result can be seen in the video below:
The Spot has an article about how it was done:
[YouTuber Denis Shiryaev] used a mix of neural networks from Gigapixel AI and a technique called depth-aware video frame interpolation to not only upscale the resolution of the video, but also increase its frame rate to something that looks a lot smoother to the human eye.