[user5994461]

I meant 1080p when I said full HD.

It takes a surprising amount of power to decode. The cheap CPU from netbooks have been struggling for a decade, especially in battery power saving mode.

Lately, they get hardware acceleration just for that. Special CPU instructions and drivers just to achieve that decently.

[voltagex_]

For Youtube in particular, they're sending VP9+opus where the browser supports it, without considering hardware acceleration. The rather anaemic Atom chips might have H264 decoding on-chip, but only Kabylake has VP9.