W3School TIY Editor
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<!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>