Hi,
In our setting, the USB camera is at /dev/video6. So we run the command:
$ gst-launch-1.0 nvarguscamerasrc sensor-id=0 ! 'video/x-raw(memory:NVMM),width=1280, height=720, framerate=30/1, format=NV12' ! fakesink nvarguscamerasrc sensor-id=1 ! 'video/x-raw(memory:NVMM),width=1280, height=720, framerate=30/1, format=NV12' ! fakesink nvarguscamerasrc sensor-id=2 ! 'video/x-raw(memory:NVMM),width=1920, height=1080, framerate=30/1, format=NV12' ! fakesink v4l2src device=/dev/video6 do-timestamp=true ! 'video/x-raw , width=(int)1920 , height=(int)1080 , format=(string)UYVY' ! nvvidconv ! 'video/x-raw(memory:NVMM) , width=(int)1920 , height=(int)1080 , format=(string)NV12' ! fakesink