However it got worse, to the point where my laptop with a quite reasonable for the task Core i5 processor and practically nothing else running would eventually reach thermal cutout temperatures (>100 degrees C) and eventually to the point where it couldn't really play videos. Surely there must be a better way.
And it turns out there is a better way, seeing as I am currently running Arch Linux on there. Also I didn't have that problem on Windows or Debian on the same computer.
Turns out that in Chromium (Not quite Chrome) there is something funny with the rendering for web based playback. This causes massive CPU usage for no good reason.
Go to the URL chrome://flags then enable "Override Software Rendering List" (#ignore-gpu-blacklist)
I'm not 100% sure what it does, but a guess for the blacklist mentioned in the # name make me think that perhaps it was trying to do all of the rendering in the CPU. Rather than getting the GPU (Integrated but still better) to do that part of the hard work, for which it is much more suited.
This may also work on Windows or Mac if you are having similar problems. It certainly hasn't hurt my computer and has made it barely load the CPU at all with video playback now.
If you have any other tips or tricks for Chrome/Chromium that make it perform better please let me know so we can help share this information.