​x
 
<!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>
​