For info on HTML5 video see: www.w3schools.com/html/html5_video.asp. There are 3 supported video sources: MP4, WebM (e.g. for MSIE 9+), and Ogg (e.g. for FireFox). The browser will use the first recognized format. Also, you will need a preview or "poster" image.

To convert a video into HTML5 video (MP4, WebM & Ogg) you can use: www.mirovideoconverter.com