(this is a re-post from StackOverflow)
Virtual webcam is typically a software only implementation that application discover as if it is a device with physical representation. The mentioned applications use APIs to work with web cameras and ability to extend the APIs and add your own video source is the way to create a virtual web camera.
In Windows there are a few APIs to consume video sources: Video for Windows, DirectShow, Media Foundation (in chronological order).
Video for Windows is not really extensible and limited in capabilities overall. It will see a virtual device if you provide a kernel mode driver for a virtual camera.
DirectShow is the API used by most video capture enabled Windows applications and it is present in all Windows versions including Windows 10 (except just Windows RT). Then it’s perfectly extensible and in most cases the term “virtual webcam” refers to DirectShow virtual webcam. Methods to create DirectShow virtual webcam discussed in many StackOverflow questions remain perfectly valid for Windows 10, for applications that implement video capture using DirectShow:
DirectShow samples were removed from Windows SDK but you can still find them in older releases:
If you provide a kernel mode driver for video camera device (your virtual webcam through custom kernel driver), DirectShow would also see it just like other video APIs.
Media Foundation is a supposed successor of DirectShow but its video capture capabilities in the part of extensibility simply do not exist. Microsoft decided to not allow custom video sources application would be able to discover the same way as web cameras. Due to Media Foundation complexity, and overhead and overall unfriendliness it is used by modest amount of applications. To implement a virtual webcam for Media Foundation application you again, like in case of Video for Windows, have to implement a kernel mode driver.