How video editing softwares change the FPS from ~29.87 FPS to 30 FPS. Where do the extra frames come from?

Question

How video editing softwares change the FPS from ~29.87 FPS to 30 FPS. Where do the extra frames come from?

In: 39

Answer 1

A spring in my room is 10 feet long and has 30 rings per foot. If I shorten it slightly it becomes 29 springs per foot or 29.5 or 29.87 but it is no longer 10 feet long. The video still has the same frames but the difference in speed has the consequence of a difference in length. Slow it down it gets longer. Speed it up it gets shorter.