The <video>
tag is meant to load in a video of a supported format (which may differ by browser).
YouTube embed links are not just videos, they are typically webpages that contain logic to detect what your user supports and how they can play the youtube video, using HTML5, or flash, or some other plugin based on what is available on the users PC. This is why you are having a difficult time using the video tag with youtube videos.
YouTube does offer a developer API to embed a youtube video into your page.
I made a JSFiddle as a live example: http://jsfiddle.net/zub16fgt/
And you can read more about the YouTube API here: https://developers.google.com/youtube/iframe_api_reference#Getting_Started
The Code can also be found below
In your HTML:
<div id="player"></div>
In your Javascript:
var onPlayerReady = function(event) {
event.target.playVideo();
};
// The first argument of YT.Player is an HTML element ID.
// YouTube API will replace my <div id="player"> tag
// with an iframe containing the youtube video.
var player = new YT.Player('player', {
height: 320,
width: 400,
videoId : '6Dc1C77nra4',
events : {
'onReady' : onPlayerReady
}
});