Displaying the WebCamTexture in Cardboard

Displaying the WebCamTexture (Android phone WebCam) in Cardboard? Like this: https://www.youtube.com/watch?v=oy5NqqDtkJ4

I tried this:

 IEnumerable Start() {
     WebCamTexture webcam = new WebCamTexture();
     GetComponent<Renderer>().material.mainTexture = webcam;
     webcam.Play();
 }

And I am attaching to the "Main Camera Left" and "Right Main Camera", but nothing is displayed.