Create a media element in C#

Question

I am trying to create a media element in my windows 8 app.

I have a media element in my XAML page

 <MediaElement Source="Assets/test.wmv"/>

This works, but instead of placing the source uri directly in the XAML, I would like to Bind to it.

<MediaElement Source="{Binding Videos}"/>

Where "Videos" is defined in the code behind the XAML page, ie, the XAML cs file.

this.DefaultViewModel["Video"]="Assets/test.wmv";

This doesn't work. How do I set the source of the video?