将HTML5 <video>作为背景设置为指定高度的div

<div id="video-background" style="height: 500px;"></div>

#video-background {
  position: relative;
  overflow: hidden;
  z-index: -1;
}

#video-background video {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: auto;
}

var video = document.createElement('video');
video.setAttribute('autoplay', '');
video.setAttribute('loop', '');
video.setAttribute('muted', '');

var source = document.createElement('source');
source.setAttribute('src', 'video.mp4');
source.setAttribute('type', 'video/mp4');

video.appendChild(source);
document.getElementById('video-background').appendChild(video);