add thumbnail to html video code example
Example: thumbnail video in html
<!DOCTYPE html>
<html lang=en>
<head>
<title>Alison falling out of bed on Medium</title>
</head>
<body>
<h1>Alison falling out of bed on Medium</h1>
<video poster="PreviewImage.jpeg" width="640" height="480" controls="controls">
<source src="AlisonFallingOutOfBed.webm" type="video/webm" />
<source src="AlisonFallingOutOfBed.mp4" type="video/mp4" />
<source src="AlisonFallingOutOfBed.theora.ogv" type="video/ogg" />
Bummer, your browser does not support the video tag.
</video>
</body>
</html>