How can I change my webcam's power line frequency setting?

Question

I'm using a Logitech C720 webcam with my PC, which runs Devuan Beowulf GNU/Linux (~= Debian 10 Buster but without systemd).

In a related, but not Linux-specific, question on SuperUser, it turns out that I need to change my webcam's power line frequency setting.

However - I have no idea how to do that. My desktop environment, Cinnamon, does not have an item in the "System Settings" dialog for it. How do I make this setting, then?

Answer 1

On the command line, you can set the uvcvideo driver's power line frequency setting to the 50 Hz value with:

v4l2-ctl --set-ctrl=power_line_frequency=1

If your webcam is not /dev/video0, add a -d /dev/videoN option with the correct number. The v4l2-ctl command comes in package v4l-utils, at least on Debian and related distributions.

Also, v4l2-ctl -L will display a list of settings available in your webcam. It will also describe the available choices for settings like power line frequency. Your webcam may have a list of available settings that is different from mine.

To make the power line frequency setting persistent, you might want to make an udev rule of it. To do that, create a file named /etc/udev/rules.d/81-uvcvideo.ruleswith the following contents:

# Set power line frequency to European
ACTION=="add", SUBSYSTEM=="video4linux", DRIVERS=="uvcvideo", RUN+="/usr/bin/v4l2-ctl --set-ctrl=power_line_frequency=1"

Answer 2

If the app you're using does not allow you to make the relevant settings, and there's no "settings applet", use an app which can make these settings.

A prominent example would be guvcview - the GNU UVC viewer program. It's a utility for capturing video from devices using the Linux USB Video Class driver (UVC). When you start it up, you'll find the power line frequency setting:

and now you can change the US-centric 60 Hz into the more common 50 Hz.

Notes:

• GUVCView may fail to start if another app is actively using the camera.
• Setting the frequency this way does not persist with system reboots.

Answer 3

Use the control utility for the Linux UVC driver

_{(This is a variant on @telcoM's answer)}

(USB) webcams are controlled by the Linux USB Video Client driver. Their device files are /dev/video0, /dev/video1 etc.

One of the driver's setting is the power line frequency, which (typically) has 3 options:

• 0 for Disabled, i.e. the driver won't account for the voltage cycle at all.
• 1 for 50 Hz (most of the world)
• 2 for 60 Hz (US and some others)

There are two alternative control utilities for this driver available on Debian systems. One is named v4l-ctl, covered in telcoM's answer, and the other is named uvcdynctrl; it is installed with the eponymous package, i.e. you need to run the following (as root or via sudo):

apt install uvcdynctrl

When the package is installed, do the following (not necessarily as a root user - it depends on the permissions of your camera's device file):

1. List the available devices to make sure you see your camera:

   uvcdynctrl -l
   

   The output should look something like this:

   Listing available devices:
   video0   UVC Camera (046d:0825)
   Media controller device: /dev/media0
   Entity 1: UVC Camera (046d:0825). Type: 65537, Revision: 0, Flags: 1, Group-id: 0, Pads: 1, Links: 0
     Device node
     Entity: 1, Pad 0, Flags: 1
   video1   UVC Camera (046d:0825)
   Media controller device /dev/media1 doesn't exist
   

2. Let's assume your device is /dev/media0:

   webcam_device="video0"
   

3. Get the current power line frequency setting:

   uvcdynctrl -d${webcam_device} "--get=Power Line Frequency"
   

   This time, the output should be just a single number. In your case it will likely be 2, which corresponds to a frequency of 60 Hz.
4. Set a new power line frequency:

   uvcdynctrl -d${webcam_device} "--set=Power Line Frequency" 1
   

If you know your device name, only the fourth command is necessary, of course.

Persisting your setting

As @telcoM notes, however, this is not a persistent setting. To make it persistent, you need to add a udev rule, to be executed when the camera is connected.

Create a file named /etc/udev/rules.d/81-uvcvideo.rules, with contents:

# Set power line frequency to 50 Hz
ACTION=="add", SUBSYSTEM=="video4linux", DRIVERS=="uvcvideo", RUN+="/usr /bin/uvcdynctrl -d$attr{name} --set=Power\\ Line\\ Frequency 1"

Notes:

• $attr{name} should hold the new attached device's name, e.g. video0, video1 etc.
• Theoretically, one could make this setting globally, irrespective of the device used. But - who knows? Maybe one of your cameras is pointed to a naturally-lit room where no powerline frequency correction is necessary.
• The above rule has not been tested (!)