What's the difference between upgrade and slow play?

Upgrade and slow play are photographic terms. The upgrade is to increase the number of frames per second when shooting, so that the slow motion is smooth and there will be no problem of picture jam. Slow play is to slow down the picture through post-processing, and it will also get slow motion, but it will have an unnatural sense of jumping.

A grid is equivalent to a frame. Generally speaking, movies are played at the speed of 24 frames per second, which is also the usual playing speed of human visual system. Upgrade means increasing the number of frames per second when shooting. For example, the normal speed is 1 sec to shoot 24 frames. If 48 frames are shot per second and the playback rate is still 24 frames per second, then it is reflected that it is 1 sec. But if you only shot 24 frames, and now you want to play it for 2 seconds, and you can only play 12 frames per second, then the picture will be lengthened through post-processing. In this case, there will be a sense of stagnation when playing, moving one by one, and it looks very uncomfortable.