获得可用视频轨道的数量 - 在线编辑器

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<head>
  <meta charset="utf-8">
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  <button onclick="getVideoTracks()" type="button">获得可用视频轨道的数量</button>
  <br>
  <video id="video1" controls="controls">
  <source src="/examples/mov_bbb.mp4" type="video/mp4">
  <source src="/examples/mov_bbb.ogg" type="video/ogg">
  您的浏览器不支持 HTML5 video  标签。
</video>

  <script>
    myVid = document.getElementById("video1");

    function getVideoTracks() {
      alert(myVid.videoTracks.length);
    }
  </script>

  <p>Video courtesy of <a href="http://www.bigbuckbunny.org/" target="_blank">Big Buck Bunny</a>.</p>

</body>
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