How can add loading animationin image in video.js

Here is my ......

<video id="example_video_1" class="video-js vjs-16-9 vjs-default-skin vjs-big-play-centered"
  controls preload="auto" width="640" height="380"
  poster="thumb url"
  data-setup='{"example_option":true}'>
<source src="video url" type="video/mp4" />
<p class="vjs-no-js">To view this video please enable JavaScript, and consider upgrading to a web browser that <a href="http://videojs.com/html5-video-support/" target="_blank">supports HTML5 video</a></p>
</video>

Code (markup):

 

You can just modify: poster="loading.gif"