Video playback performance issue Ubuntu 18.04

This bug is worth a look at.

https://bugs.launchpad.net/ubuntu/+source/nux/+bug/1767468

The system is looking for unity support, doesn't find it (because the tool that checks for it has been remove) and so disables hardware.

Worked for me anyway.

Edit: issue the command sudo rm /etc/X11/Xsession.d/50_check_unity_support this has been reported as a successful workaround to the issue.