[Linux] access the webcam at the same time

找了一陣子終於看到了
https://askubuntu.com/questions/165727/is-it-possible-for-two-processes-to-access-the-webcam-at-the-same-time

$ git clone https://github.com/umlaeute/v4l2loopback.git
$ cd v4l2loopback
$ make
$ sudo make install

$ sudo depmod -a

$ sudo modprobe v4l2loopback devices=2

gst-launch-1.0 v4l2src device=/dev/video0 ! tee name=t ! queue ! v4l2sink device=/dev/video1 t. ! queue ! v4l2sink device=/dev/video2