Here we have a video clip that is rendered in the page (using WPF/E of course) on the client site.
Everything that appears apart from the video is determined by a remote call to the ad server using a simple JavaScript include - which could easily be (for instance) a timed reload or in response to a user action or a trigger in the video.
To demonstrate that I have two different ads encoded in the current sample remote .js file.
WPF/E is very clever ;). See this post for more information.