WebRTC; Using a virtual WebCam

Hello, I want to simulate a Webcam, so I want to use that virtual Webcam Driver on a Website like Chatroulette which uses WebRTC. I tried it with ManyCam & Webcamoid (OpenSource) and with that softwares its working perfectly on Chatroulette. But I have another website which also uses WebRTC but on that website, ManyCam and similar softwares arent working. So if you know why and if you can fix that, pls send me a message.