Multiple Window Capture (Xcomposite) get black screen

[hank1]

Hi, I am ubuntu 20.04 user with following gst-launcher command :
gst-launch-1.0 v4l2src device=/dev/video0 ! xvimagesink
gst-launch-1.0 v4l2src device=/dev/video1 ! xvimagesink

For some reason, I cannot use this camera as a Video Capture Device (V4L2).
I can detect the device, but not a single camera works.

So I was kept using Window Capture for 'Streaming'.
And now, I need more than one camera.

But when I set one more camera, one get black screen.
How can I solve this?

 

[hank1]

why does obs does not support more than one window capture?