Will it be a drain on older CPU’s ?
From some quick scanning of HTML5 info, it seems the advantage is to use several video formats:
MP4
WebM
Ogg
3GP
FLV
It also seems that your browser determines which format is viewable. Old browsers will revert to Flash.
Newer browsers will load and play the HTML5 formats:
IE 9+
Firefox 4+
Crome 6+
Opera 10.60+
Safari 4+
iPhone 3+
iPad 1+
Android 2.1+
BlackBerry 6+
Windows Phone 7+
Not, it will be a Gate...............[Obscure Semiconductor double entendre joke]
Old PCs need to user a newer browser for this to work. Microsoft is phasing out support for all versions of IE prior to 11 in a push to make HTML5 a web standard for all platforms.