​x
 
<!DOCTYPE html>
<html>
<body>
​
<video id="myVideo" width="640" height="360" poster="/i/logo/w3v.png" controls>
  <source src="/i/video/shanghai.mp4" type="video/mp4">
  <source src="/i/video/shanghai.ogg" type="video/ogg">
  您的浏览器不支持 video 标签。
</video>
​
<p>单击该按钮可更改封面图像。</p>
​
<button onclick="myFunction()">试一试</button>
​
<script>
function myFunction() {
  document.getElementById("myVideo").poster = "/i/photo/shanghai.jpg";
}
</script>
​
</body>
</html>
​