<html>
<body>
<button onclick="getTextTracks()" type="button">Get the number of available text tracks</button>
<br>
<video id="video1" controls="controls">
<source src="mov_bbb.mp4" type="video/mp4">
<source src="mov_bbb.ogg" type="video/ogg">
<track src="demo_sub.vtt">
Your browser does not support HTML5 video.
</track></source></source></video>
<script>
myVid=document.getElementById("video1");
function getTextTracks()
{
alert(myVid.textTracks.length);
}
</script>
<p>Video courtesy of <a href="http://www.bigbuckbunny.org/" target="_blank">Big Buck Bunny</a>.</p>
</body>
</html>