Following on from the previous post on revisiting convolution in processing and trying to tie that in with my previous explorations of the desktop as a performance space and feedback generator wouldnt it be good if there was a way to pass the desktop as video into processing scripts in a similar way to that in which ffmpegs' x11grab allows us to open a window which follows the mouse focus around the desktop like a virtual webcam ?
Turns out there is. A friend had told me about V4l2loopback previously, a way of creating virtual webcams in Linux and then thinking about it the other day I came across this post which describes how to do it https://narok.io/creating-a-virtual-webcam-on-linux/ but that author streams a video file rather than what I want which is the same input as I get from x11grab. Why ? If we can create a virtual webcam we can use that as an input for processing so we can extend the possibilites of desktop feedback loops .
TLDR: do this on Debian based systems
*edit 2026 make sure before running these commands that you have the kernel headers for your particular kernel installed before running these commands, otherwise it will fail to work.
install this
sudo apt install v4l2loopback-dkms
run this command
sudo modprobe v4l2loopback devices=1 video_nr=10 max_buffers=2 exclusive_caps=1 card_label="Default WebCam"
then this
ffmpeg -f x11grab -follow_mouse centered -framerate 10 -video_size 640x480 -i :0.0 -f v4l2 -vcodec rawvideo -s 640x480 /dev/video10
To check that it is working open obs-studio and select "Default WebCam (v4l2loopback-Default_WebCam-video)" as the video input device - if this option isn't there recheck the previous steps.
Then open a script in processing which uses a webcam for input ( ie the convolution scripts ive been working on ) and experiment.
