Some modern camera models can be directly connected to the computer through USB and be detected as a webcam. That’s the easiest setup, but beware that this mode of operation might need special programs/drivers with no support for Linux. The more general approach is to use some video capture device that can take the HDMI output of the camera, stream it through USB and present itself as a USB webcam.
Camera conversion to USB webcam
In my case, the camera is a Fujifilm X-E3 which can send clean video through its HDMI output and I use Elgato Cam Link 4K to convert the video signal to USB. Once the camera is connected to the computer, it is recognized as any regular USB webcam thanks to the open source uvcvideo kernel module. Linux kernel v5.14 fixed an issue with the reported pixel format by the Cam Link, so any Linux distribution with a recent kernel (or backported patches) should work with this device out of the box.
Virtual webcam in OBS Studio
OBS Studio is very useful to mix audio and video streams in real time. For instance, I use it to sync the audio of my mic or capture my computer desktop overlaying my cam in a corner of the stream.
Since version 26.1 (Dec 2020), OBS natively provides a Virtual Camera output, which allows to catch its stream from any video chat application. OBS itself will appear as a new webcam device. Enabling this option requires the kernel module v4l2loopback, which might not be installed by default.
In Fedora 35, OBS Studio v26.1+ is available as a flatpak
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$ sudo flatpak install flathub com.obsproject.Studio
The kernel module v4l2loopback is available in the RPMFusion repository. Once RPM Fusion is enabled in your system, install v4l2loopback with the following command:
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$ sudo dnf install kmod-v4l2loopback
Once v4l2loopback is installed, restart OBS Studio and the new option Start Virtual Camera will appear below the Start Recording button.
Note: Some video call applications limit the video resolution of the webcam device (e.g. MS Teams accepts 1280x720 max). In such a case, set the required resolution of the output stream in OBS in Settings > Video > Output (Scaled) Resolution.
Virtual microphone
One limitation of the Virtual Camera in OBS is that it only contains the video stream. If you want to use the audio stream from OBS in your video call as well, you will need to redirect its audio into a virtual mic. This can be done with PulseAudio by creating a null-sink device as virtual speaker and remapping its monitor to a new audio source as virtual mic. These two virtual audio devices allow to redirect the audio from any application to any other application.
Create virtual speaker
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$ pactl load-module module-null-sink sink_name=Virtual-Speaker sink_properties=device.description=Virtual-Speaker
Remap monitor of virtual speaker as virtual mic
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$ pactl load-module module-remap-source source_name=Virtual-Mic master=Virtual-Speaker.monitor
The advantage of this approach is that it does not depend on any specific audio device. The previous commands should work in any system with PulseAudio.
Redirect audio in OBS to virtual speaker
Set the monitoring device of your stream in OBS to Monitor of Virtual Speaker. This setting is located in Settings > Audio > Advanced > Monitoring device.
All audio sources of your stream in OBS should be real audio devices (i.e. the real mic)
In the video call application:
- choose OBS Virtual Camera as webcam
- choose Virtual Mic as mic or, alternatively, set the Virtual Mic as default mic in PulseAudio