DirectShow (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/directx9_c/directX/htm/directshow.asp), formerly Active Movie, is a component of the Microsoft DirectX 8+ (http://www.microsoft.com/directx/) family of multi-media APIs.
It is characterized by streams of data that are represented and controlled by a graph of data filters.
Filters can have input and output "pins" that permit their interconnection. Pins are typed so that only legal interconnections are permitted.
A filter graph may represent data moving through memory, data moving through hardware, or a combination of the two.
DirectShow is closely associated with the new WindowsDriverModel? (WDM) supported in Windows98 and WindowsNT 5.0.
From DirectX FAQ (http://www.microsoft.com/windows/directx/default.aspx?url=/windows/directx/productinfo/faq/):
Q: In earlier versions of DirectX, I had to install DirectX Media. Do I still need it?
A: No, not with DirectX 9.0. The key part of DirectX Media for video capture, Microsoft DirectShow(R), has been integrated into DirectX.
Some resources for developers: