I don’t know how or why that would work, but from quickly looking in the article it looks like it will also re-encode the video so you’re not saving any time.
@daniel47 yeah 
It may seem inappropriate, but perhaps it’s to avoid exporting or importing a previously stabilized portion of the video.
I tried this filter, but it didn’t work either, especially since I had previously rotated the video to fit the vertical profile.
The thing is, Avidemux is very orthodox, but it does it, even though its philosophy isn’t “division of labor,” but rather a strange reductionism!
@daniel47, I was curious about the “choppy” filter, how lethargic the video, then if you can apply stabilization… it’s a new MacGyverism that I’ll have to try more, as an alternative to the “ffmpeg > timestamp”!
Speed Up or Slow Down a Video
Use the setpts (set presentation timestamp) video filter (-vf). The argument to the setpts filter is a formula for how to set the timestamp. Some example values:
setpts=0.66*PTS- roughly 1.33x speedsetpts=0.5*PTS- double the speedsetpts=0.25*PTS- quadruple the speedsetpts=2.0*PTS- half the speed
For example, to double the speed of a video:
ffmpeg -i path/to/original/file.mp4 -vf "setpts=0.5*PTS" path/to/output/file.mp4
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