Alternatives:

Firefox, YT only: https://www.mrfdev.com/enhancer-for-youtube The improved playback speed ranges from 25% to 400% (also 800% but without audio) in adjustable increments.

For offline videos, VLC also is capable of changing playback speed.

Are there video players or plugins having "dynamic" speedup? Like, playing everything faster by a fixed amount isn't optimal. Maybe the words could be said 3x faster, the breaks between words however be kept at 1.5x faster as to not make it one big mush, and space between sentences some third amount.

Edit: I see some podcasts app have something similar (albeit opposite). It shortens dead space between two people talking and try to not affect the speed of their speech.

Skip Silence[1] for chrome does exactly that.

[1]https://vantezzen.github.io/skip-silence/

This one is recommended for Firefox: https://addons.mozilla.org/en-US/firefox/addon/videospeed/

I find that most videos are understandable up to 3x. I watch most of them at 2.5-2.8x, down to 2x for people that talk fast or with a hard accent. Same for podcasts.

music videos must be fun, then

Nightcore is a remix genre of music that is basically "turn the speed (and pitch) up". It can be surprisingly good.

Can't remember the last time I watched a music video!