On my laptop, the Chromium CPU usage without hardware acceleration goes way higher. Both screenshots were taken on my old, but still quite powerful desktop. This is Chromium from the Ubuntu (18.04) repositories without GPU accelerated video decoding playing a 1080p YouTube video: The instructions cover only Intel and Nvidia graphics cards, as I don't have an ATI/AMD graphics card to try this, nor do I have experience with such graphics cards, but from what I've read, this should work with ATI/AMD graphics too. This article explains how to install a Chromium beta or development build which includes a patch that enables VA-API on Linux, bringing support for GPU accelerated video decoding, which should significantly decrease the CPU usage when watching HD videos online.

That's because Chrome / Chromium (Firefox too but there's no way to force this) doesn't support hardware accelerated video decoding on Linux.

You may have noticed that watching HD videos from Youtube and other similar websites in Google Chrome or Chromium browsers on Linux considerably increases your CPU usage and, if you use a laptop, it gets quite hot and the battery drains very quickly.

Chromium ubuntu