video speed-up & slow down - 2020

In this chapter, we want to play with a movie clip to make it play faster or slower:

We're going to use pts (presentation time stamps) to speed-up our video of a factor 4:

ffmpeg -i TheGoodTheBadAndTheUgly.mp4 -vf  "setpts=0.25*PTS" UpTheGoodTheBadAndTheUgly.mp4

We need to understand that it is inevitable to drop frames to ply the video faster. Actually, the size of the mp4 video has been reduced to 11MB from 19MB.

This is the opposite of speeding up. We want the movie slowed down factor of 4:

ffmpeg -i TheGoodTheBadAndTheUgly.mp4 -vf  "setpts=4*PTS" DownTheGoodTheBadAndTheUgly.mp4

In the process of slowing down, the size of the movie increased to 29MB from 19MB.