How can HTML5 player be used on OS X Sierra & Safari 10.0.1 ???

My MacBook Pro is running much hotter playing youtube videos than it ever did with El Capitan. Even tho' a clean install was performed with Sierra I've never had so many problems w/ a Mac OS, just one problem after another. I'm about ready to redo the clean install -- not that I expect improvement b/c I think the difficulties lie in the OS.

HTML5 is built-in to Safari, it may depend on the website you are accessing on whether it is used. For YouTube you may need to first visit the following URL to 'turn on' HTML5 for YouTube.

YouTube HTML5 Video Player

When HTML5 was new Safari was one of the better web-browsers in terms of supporting it, however sadly it seems that Apple have neglected this and according to some reports have not kept up with newer changes in the HTML5 spec. This should not prevent playing (most) HTML5 video content though.

You can test HTML5 video support here - http://www.quirksmode.org/html5/tests/video.html

You can test HTML5 general compatibility here - https://html5test.com/index.html even Safari 10 scores much lower than the current Google Chrome and Firefox browsers. 😟

Safari only supports H.264 and does not support OGG/Theodora or WEBM however H.264 is far, far more common and is what YouTube and Netflix use as examples.