You can requestFullscreen on an Video or Canvas element to ask user to give you permisions and make it full screen.
Let’s consider this element:
<video controls id="myvideo">
<source src="somevideo.webm"></source>
<source src="somevideo.mp4"></source>
</video>
We can put that video into fullscreen mode with script like this:
var elem = document.getElementById("myvideo");
if (elem.requestFullscreen) {
elem.requestFullscreen();
} else if (elem.mozRequestFullScreen) {
elem.mozRequestFullScreen();
} else if (elem.webkitRequestFullscreen) {
elem.webkitRequestFullscreen();
} else if (elem.msRequestFullscreen) {
elem.msRequestFullscreen();
}