I’m on a 2019 Intel MacBook Pro: 2.6 GHz 6-core i7, 64 GB RAM. The machine is still more than powerful enough for normal desktop work and software dev, but YouTube in Chrome has become borderline unusable for me. My internet is fine, Safari plays the same videos smoothly, and YouTube “Stats for nerds” shows plenty of buffer but the decoding makes youtube unusable in chrome for me.
Download the video with yt-dlp & play it in mpv you'll see it even flies on a potato.
Play the same in browser and it'll be dropping frames left and right.
[1] https://www.phoronix.com/news/dav1d-0.5 (it's mislabled as a core i3, but the 3770K is a core i7).
For encoding, you can always write a simple encoder that use only the features that were present in mpeg2, and it will be about as efficient as mpeg2 as well. Newer codecs has more features that allows more efficient encoding, at the cost of more processing.