Render to Video Input/Output cards (e.g. BlackMagic Design's Decklink) as a Window in .NET

Question

I am investigating the possibility of treating a video input/output card as a Window so that I can render graphics to it from .NET. It would need the ability to handle transparency so that I can key the rendered graphics over incoming video.

I haven't found anything that does exactly this - some SDKs allow you to render graphics, but you have to use their API to draw them, rather than using standard .NET WPF/Windows Forms routines.