Enabling Single Webcam for Multiple Applications Access in Linux

A webcam can not be accessed by two or more applications simultaneously. The solution is you can duplicate the video stream and make it available for any application. In short, you create virtual webcam.
First, a webcam is commonly detected on /dev/video*. Before you go through the steps to duplicate video stream, you should check whether your webcam is working. You can try to capture video using VLC by this command. (For example, your webcam is on /dev/video0)

$ vlc v4l2:///dev/video0

If it doesn't work, you can try to change its mode to 0777 and make sure there's no other applications accessing it. If it still doesn't work, you can buy a new webcam. Seriously. Don't buy cheap and unknown-brand webcam. I have $5 webcam and it had wasted my time.

$ apt-get install ffmpeg linux-generic v4l2loopback-dkms

FFmpeg is main application that will access your webcam and duplicate its video stream. V4L2loopback is needed to create multiple virtual capture devices (loopback devices) in Linux which is used by FFmpeg to store duplicated video stream and accessed by other applications. For example, I want to enable two loopback devices. The new devices will be available on /dev/video* in a sequence.

$ modprobe v4l2loopback devices=2

Then, you can duplicate your webcam.

$ ffmpeg -f v4l2 -i /dev/video0 -f v4l2 /dev/video1 -f v4l2 /dev/video2

Or, you can also set the video resolution.

$ ffmpeg -f video4linux2 -s 800x600 -i /dev/video0 -codec copy -f v4l2 /dev/video1 -codec copy -f v4l2 /dev/video2

After you don't need the loopback devices, you can remove it.

$ modprobe -r v4l2loopback

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