how to create thumbnail image from video url

I'm trying to get a thumbnail of a video url.
i want it to put in player.

<div id="myElement">Loading the player...</div>
<script type="text/javascript">
jwplayer("myElement").setup({
    file: "/uploads/example.mp4",
    image: "/uploads/example.jpg",
});

1. Is there an easy way to do it?
2. What about codecs? Will I have to deal with it?
3. Any video type is suported?