I've been working a MediaDetector control over the weekend. It will be a simple control to easily detect what type of media you have, codecs, streams, etc. It also allows you to get thumbnails for video at any specific time. Since the control is not finished, but the the helper class is, I have commited that class to the MediaKit.
It's pretty simple to use:
MediaDetector det = new MediaDetector();
for (int i = 0; i < 100; i++)
BitmapSource bitmap = det.GetImage(TimeSpan.FromSeconds(i));
I'll let you guys know when the WPF control is ready.