DirectShow is a collection of instructions, functions and conventions that can be used for conversion libraries and programs of videos provided by Microsoft.
In a very brief explanation, it means directshow compatible camera can operate with a common command (programmed).
If PC recognizes USB camera, the application software can operate without using the one attached to the camera.
(It may be necessary to separately require the PC to recognize the camera.)
In other words, you can use application software from another company. (Due to common instructions (programmed).)
You can obtain and use necessary software according to the application such as: Viewer software, measures images software, automatic visual inspection software, 3D synthesis software, and so on.
There are various companies that actually sell only software.
However, there are several types of shadow image format output from the camera and it is necessary for the application software to support this video format.
Video formats include YUY 2, RGB 24, RAW 16, etc.
Those sold only by software cover a typical video format but some of these items attached to the camera correspond only to the video format of that camera.