how to preview video in html code example

Example 1: video tag thumbnail

<video controls poster="/images/w3html5.gif">
  <source src="movie.mp4" type="video/mp4">
  <source src="movie.ogg" type="video/ogg">
  Your browser does not support the video tag.
</video>

Example 2: how to display the first frame of the video element in html

Try appending  #t={seconds} to the end of your src value. Here's an example:

<video width="300" height="150">
   <source src="testvideo.mp4#t=0.1" type="video/mp4" />
</video>

It works fine on Chrome/Firefox and many other browsers.