Elphel Development Blog

Convert ip cam to web cam in Linux for Jitsi, Zoom, etc.

Basically, one need to direct the ip cam stream (mjpeg or rtsp) to a virtual v4l2 device which acts like a web cam and is automatically picked up by a web browser or a web cam application. This can be easily done by gstreamer or ffmpeg.

Quick setup

Install and create a virtual webcam

~$ sudo apt install v4l2loopback-dkms
~$ sudo modprobe v4l2loopback devices=1


Direct the stream

The options below are for gstreamer/ffmpeg and rtsp/mjpeg streams:

gstreamer:
# rtsp stream
~$ sudo gst-launch-1.0 rtspsrc location=rtsp://192.168.0.9:554 ! rtpjpegdepay ! jpegdec ! videoconvert ! tee ! v4l2sink device=/dev/video0 sync=false
# mjpeg stream
~$ sudo gst-launch-1.0 souphttpsrc is-live=true location=http://192.168.0.9:2323/mimg ! jpegdec ! videoconvert ! tee ! v4l2sink device=/dev/video0


ffmpeg:
# rtsp stream
~$ sudo ffmpeg -i rtsp://192.168.0.9:554 -fflags nobuffer -pix_fmt yuv420p -f v4l2 /dev/video0
# mjpeg stream
~$ sudo ffmpeg -i http://192.168.0.9:2323/mimg -fflags nobuffer -pix_fmt yuv420p -r 30 -f v4l2 /dev/video0


Finally

Start a video conference application, select the webcam from the menu (/dev/video0).
Test link: meet.jit.si

Details

Requirements

• ffmpeg (2.8.15) or gstreamer (1.8.3)
• IP camera capable of streaming mjpeg or rtsp – in this case it’s Elphel NC393

IP camera setup

• rtsp stream ports for Elphel NC393 cameras: 554, 556, 558, 560
• mjpeg stream ports for Elphel NC393 cameras: 2323, 2324, 2325, 2326
• stream resolution/fps: 1920×1080, 30fps
• ffmpeg for mjpeg stream – “-r 30” sets fps – the default ffmpeg setting is 25 fps

Useful commands

Print web cam settings:
v4l2-ctl -d 0 --all
Gstreamer play mjpeg:
gst-launch-1.0 souphttpsrc is-live=true location=http://192.168.0.9:2323/mimg ! jpegdec ! autovideosink
Gstreamer play rtsp:
gst-launch-1.0 -v playbin uri=rtsp://192.168.0.9:554 uridecodebin0::source::latency=0
Test stream for web cam:
sudo gst-launch-1.0 videotestsrc ! tee ! v4l2sink device=/dev/video0

Comments

• Gstreamer 1.8.3 didn’t work without tees in the pipeline.
• modprobe v4l2loopback can create multiple devices