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virtualvideo allows you to write simple programs that feed images to a v4l2loopback device

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VirtualVideo allows you to write simple programs that feed images to a v4l2loopback device.



Install virtualvideo with: pip3 install --user virtualvideo

Install ffmpeg(preferably with your systems packagemanager) and v4l2loopback. Installing v4l2loopback can be tricky and i suggest using dkms to install/build it. (If you're using Arch-Linux theres an AUR Package for you: v4l2loopback-dkms).

Example shows how to use the virtualvideo package.

Running the Example

To run the example:

$ sudo modprobe v4l2loopback video_nr=XX exclusive_caps=1
$ cd examples
$ python3

Adjust the fvd.init_output(42, 1280, 720, fps=30) line in to use the same video_nr as you used to initialise the v4l2loopback device. Or use video_nr=42 when initing v4l2loopback.

Then you should be able to open/view the webcam for example with vlc (or on You then should see a red goldfish getting blurred and unblurred. See example/ for a gif.


  • Check if the user is allowed to access the device, otherwise change permissions of /dev/videoXX

  • Use following code to check if ffmpeg is working properly $ ffmpeg -loop 1 -re -i foo.jpg -f v4l2 -vcodec rawvideo -pix_fmt yuv420p /dev/videoXXX

  • If not checkout the v4l2loopback github and wiki

  • If the image is distorted try unloading and loading the module, maybe check $cat /sys/devices/virtual/video4linux/video69/format for the format you should use

  • If you want to change the format or the pixel format unload the module

  • If you cannot unload the module, check processes that access /dev/videoXX ($ fuser /dev/videoXX) and kill them

  • If you get an pixel_format not supported error, try yuyv422 as pixelformat e.g.: fvd.init_output(...,pix_fmt="yuyv422") or $ ffmpeg -loop 1 -re -i foo.jpg -f v4l2 -vcodec rawvideo -pix_fmt yuyv422 /dev/videoXXX


This Module relies heavily on v4l2loopback and ffmpeg-python

The fish.jpg used in the examples is "Goldfish" by Melinda van den Brink

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