How do I make a virtual webcam? (Ex: Manycam)

Question

I've been looking into creating my own video capture and streaming software (I'm just looking to challenge myself, so this isn't a crucial project) and have found all the information that I need other than how to stream the video as a virtual webcam.

For example, Manycam will take several different inputs (I have this covered), and when you go into a program, such as Skype, it is listed as a webcam source. When you select it as a webcam source, then whatever you have set the Manycam software to stream will be shown.

I'm not asking for the answer. As I said, I'm after a challenge. I'm specifically after how is this achieved and where can I begin to research this? I've been digging through Google and have only found information on screen recording, which I have covered.

Thank you!

Solution

There are a few APIs in Windows which address video capture and offer capabilities to enumerate devices, and use specific device for capture: Video For Windows, DirectShow, Media Foundation.

To cut long story short, the absolute majority of existing apps use DirectShow, including Skype. In DirectShow you can create a software user mode video source and implement virtual video device to custom stream video, duplicating feeds or synthesizing whatsoever. See the following topic with links into others questions discussing exactly this topic, ans also pointing to sample projects: Virtual webcam input as byte stream.