Accessing 4 USB camera javascript getusermedia HTML5 via webrtc, how ?

There are working examples , which work for 2 usb cameras but if I add 3rd usb camera connected to my PC, I get error.

Let me know if 2 usb cameras limit is a result of hardware, software, getUserMedia.

If you know working 4 usb cameras examples, please let me know

https://developer.mozilla.org/en-US/docs/Web/API/MediaDevices/getUserMedia
2 usb cameras example Accessing Multiple camera javascript getusermedia