<!DOCTYPE html>
<html>
<body>
<button onclick="getTextTracks()" type="button">获得可用文本轨道的数量</button>
<br />
<br />
<video id="video1" controls="controls">
<source src="/example/html5/mov_bbb.mp4" type="video/mp4">
<source src="/example/html5/mov_bbb.ogg" type="video/ogg">
<track src="demo_sub.vtt">
Your browser does not support HTML5 video.
</video>
<script>
myVid=document.getElementById("video1");
function getTextTracks()
{
alert(myVid.textTracks.length);
}
</script>
</body>
</html>