DirectShow

DirectShow is a large collection of objects for working with multimedia data. The library mainly consists of "filters" - objects which process data - which you'd then connect up into "filter graphs." For example, you have filters that read data from a file, and filters which compress/decompress video streams, and filters that render video to the screen. The number of filters is pretty immense, though, and it includes a framework for writing your own if what you want to do isn't present.

DirectShow is part of the DirectX library.