A: 

I recently wrote an application to analyze video using C# and AForge.NET; it was a pretty nice library. You can do all of the overlay in .NET, which is a lot easier (although slightly less efficient, but who cares) than trying to do it with some of the video APIs out there (like directshow, which can be difficult to get decent overlay, particularly with the DirectX-ish renderers)

kidjan
Thanks. I am currently looking into opencv+emgu. I will also look at AForge and see which one fits my requirement. BTW, I looked into Expression Encoder 4 (EE4) which, frankly, would have been my preferred choice as needed to upgrade my skill-set. However, the stumbling block was, building an authoring tool to do this would be non-trivial work, as I would have to build my own timeline and rendering engine. EE4 doesn't have playback hooks from the SDK other than for Live preview.I will continue to research and post my finding later.Thanksrock-meister
rock-meister