Using digicam as a webcam on Linux

Buying a proper webcamera can turn out pretty costly, so why not fetch your old camera from a cellar and plug it into your laptop? How hard can it be?

I recently dug out a pretty old Canon EOS 550D, and since I only have a poor built-in webcam, that was a chance to improve my video quality significantly!

Once plugged into a USB port, the camera is detected just as storage. We need two things to make it work properly:

1. Stream the video feed from it
2. Pipe this feed into a virtual video input device

🔗Grabbing the video feed

The first step is pretty simple — just use gphoto2:

$ # Check if the camera is detected correctly
$ gphoto2 --abilities
Abilities for camera             : Canon EOS 550D                              
Serial port support              : no
USB support                      : yes
Capture choices                  :
                                 : Image
                                 : Preview
                                 : Trigger Capture
Configuration support            : yes
Delete selected files on camera  : yes
Delete all files on camera       : no
File preview (thumbnail) support : yes
File upload support              : yes
$ # Now get the video!
$ gphoto2 --stdout --capture-movie
Capturing preview frames as movie to 'stdout'. Press Ctrl-C to abort.
<enjoy the matrix>

🔗Creating a fake video device

The second piece of the puzzle is v4l, in particular, v4l2loopback. If you’re using Arch like me, you can just install it:

pacman -S v4l2loopback-utils

This will also install the required DKMS package to bring in the kernel module named v4l2loopback.

Now run

sudo modprobe v4l2loopback

To create a virtual video device. You can check the kernel logs for the exact path; in my case, it was /dev/video2

Now we can stream the video feed from the camera to that device using ffmpeg!

gphoto2 --stdout --capture-movie | \
ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video2

NB: If this command fails with a permission error, make sure that your user is in video group: sudo usermod -aG video $USER

Now we need to enable this module on boot:

v4l2loopback

And finally let’s set default module options:

options v4l2loopback exclusive_caps=1 card_label="GPhoto2 Webcam"

NB: After reboot, this module will load very early, earlier that other camera drivers, so the device path will be /dev/video0

Reboot and verify that this command still works:

gphoto2 --stdout --capture-movie | \
ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video0

🔗Automation

Manually running a script every time we join a video call is not fun. Luckily, we have two ways of solving this, pick one!

🔗Full

Let’s automate staring the capture using udev.

First, create a udev script

#!/bin/bash

# Uncomment the next line in you want the camera to focus before capturing
#gphoto2 --set-config autofocusdrive=1
gphoto2 --stdout --capture-movie | \
ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video0 &

And now we can use gphoto2’s screet to generate udev rules for us:

#                   magic script                                     script name
/usr/lib/libgphoto2/print-camera-list udev-rules version 0.98 script gphoto2-start-capture | \
sudo tee /etc/udev/rules.d/90-libgphoto2.rules

The script will be called when you connect any camera, which is nice IMO.

🔗Semi-automation

Running the capture all the time consumes CPU, so maybe it’s not something you want. Worry not, we can still make a nice button to start capture in KDE.

Go to Setting → Removable Storage → Device Actions. We’re going to add two new actions:

After relogin and reconnecting the camera, you will see these two new action in the device menu:

NB: If you choose this approach, remember to undo the “Full automation” step by either removing /etc/udev/rules.d/90-libgphoto2.rules or commenting out all the lines in /lib/udev/gphoto2-start-capture

🔗Mount

There is not much use for a camera that which lies on your table. We need a proper mount for it!

After some research, I found RAM Mounts. They are modular, so you can build anything you need for your desk setup. They also have two types of labels on each part: either “PATENTED” or “PATENT PENDING”. Probably this is the reason why they are so damn expensive.

Luckily, after some more research, I found Arkon Mounts, which don’t have these labels and are twice cheaper.

And now I have this amazing attachment to my monitor mount:

🔗Battery

If you’re following this guide, pretty soon you’ll find out that the camera’s battery dies very fast: in about two hours. Charging it after every video call is pretty cumbersome, and after a couple of months the capacity will be reduced significantly.

The last pice of the puzzle it a dummy battery (bought here):

I think that the intendant purpose is to power you camera from a “Power Bank”, but we can just plug it into any USB port.

🔗Did it worth it?

Overall, I’m happy with the result. I hate buying new things when I already posses something that has the required capabilities.

I had to buy two new things though: a “dummy battery” and a mount, but both of them can be used for other purposes.