This one is gonna be about the standard WebM video container and the integration on a WordPress blog, like this one
One) Get a WebM video file This is obvious but some people don’t know how to get one. To achieve this you can use Arista transcoder or your favourite video editor/transcoder.
Two) Install two plugins on your WordPress installation: PJW Mime Config and MediaElementJS – HTML5 Audio and Video. The first allow us to add a new MIME type extension: webm file extension, video/webm MIME type; the second one inserts webm files on Posts or Pages with a player or another depending on the navigator.
Three) There is no three
Get more info from this plugins on respective websites or/and consulting readme files.