I don't know if crop to fill is posible with a video. But you can generate an image from the video that fills the whole area:
Article.Image.GetUrl(600, 200); //Width and height HAVE to be even numbers
Article.Image.GetUrl(600, 200, 5.0); //Last variable is percentage into video
But then you have to open the video when the user clicks on the image. For example in a javascript popup.
That doesn't exactly answer your question, but you'll at least be able to show a bigger video player as well as having a thumbnail of which ever size you want.