Why is the VideoRendererElement? The MediaElement works fine for me.
The MediaElement does work fine for most people. The problem is that the MediaElement only allows you to supply a Uri source. The developer does not have any flexibility to create their own custom video solutions.
Can't I just use the InteropBitmap and update that buffer?
You can. Sure. The problem is that execution path is many times slower than MediaElement (and therefore VideoRendererElement) and you get tearing in the video. There is a new WriteableBitmap that is comming in .NET 3.5 summer update, but that probably won't be performant or optimized for video.
What is a FOURCC?
A FOURCC is a four character codec code. If you are just doing uncompressed updates, you do not need one. When you load up a media file, DirectShow uses the FOURCC to determine what codecs are compatible with your media. For example, there is a Motion-JPEG codec that comes with Windows. It is configured to be loaded with a FOURCC of MJPG.
My video is upside down or sideways! What do I do?
If you are supplying uncompressed samples, like a Bitmap, when you initialize the renderer, supply a negative value for the width or height will fix that.