Video in Silverlight is played by using the built-in MediaElement class. You might have seen some video frameworks like Silverlight Media Framework, Expression Encoder Player or Open Video Player, they all are based on this class. Though these frameworks look quite complex, in reality they are just wrappers around the built-in MediaElement or SmoothStreamingMediaElement classes and all that they do is adding design, control buttons and some extra functionality like advertisement and diagnostics. So you can build such video player by yourself.
The simplest media player
Here is the simplest code which will work:
<MediaElement
Source="http://ecn.channel9.msdn.com/o9/content/smf/progressivecontent/wildlife.wmv" />
It will start playing video as soon as the page is loaded and the video fills the entire page uniformly (keeping its aspect ratio).

If it doesn’t work, make sure that the address of your page looks like `http://…` and not `file://…`. You can fix the url in this way by adding a web application project to your solution and running it.
Now I will explain how to improve the code above so that it looks more like a video player.
Read more of this post