For the specific application you are describing, it seems AForge.NET would suffice. If you need to overlay text over your captured video frames, perhaps you can do something exactly like I did on another personal project that I started,
Screencast Capture. This application captures a video stream from the desktop screen, adds a few texts on top of it, then saves it to the disk. It works by using AForge's VideoPlayer and ScreenCaptureStream, but you can replace them by AForge.NET's
VideoCaptureDevice.
Here is where the application processes a new frame being received by the stream:
It creates a Graphics object from the image (line 503) then passes it along to other classes that draw things over the frame. For example, one of the classes is responsible for writing any keys being pressed to the image. Its code can be seen at