[Doc] Additional information about Udev rules for virtual webcams.

[tkapias]

• I have checked that a similar feature request does not already exist.

Issue

I use scrcpy as a virtual webcam with the new Video4Linux feature, but today I've noticed that some applications can't list the device I've created.

It seems that, awaiting Pipewire support, it's common to use the symlink /dev/v4l/by-id/ to list webcams.

This symlink is created by an existing udev rule in most distributions, but only for USB physical devices, not virtual ones.

Solution

I found the v4l2loopback issue #96 indicating to manually create another udev rule.

It works for me and I think that it might be useful to add this information to the doc.

Context

OS: Debian GNU/Linux trixie trixie/sid x86_64
Kernel: 6.6.13-amd64
WM: i3 (X11)
scrcpy: 2.3.1 https://github.com/Genymobile/scrcpy
Dependencies (compiled / linked):

• SDL: 2.30.0 / 2.30.0
• libavcodec: 60.31.102 / 60.31.102
• libavformat: 60.16.100 / 60.16.100
• libavutil: 58.29.100 / 58.29.100
• libavdevice: 60.3.100 / 60.3.100
• libusb: - / 1.0.27

Persistent v4l2loopback devices conf:

• /etc/modules-load.d/v4l2loopback.conf

v4l2loopback

• /etc/modprobe.d/v4l2loopback.conf

options v4l2loopback devices=2 exclusive_caps=1,1 video_nr=0,2 card_label=android-cam,fake-cam

• /etc/udev/rules.d/60-persistent-v4l2loopback.rules
  The solution suggested above.

KERNEL=="video*", ATTR{max_openers}=="?*", SYMLINK+="v4l/by-id/v4l2loopback-$attr{name}-video"

Systemd service to toggle the webcam:

• ~/.config/systemd/user/scrcpy-cam.service

[Unit]
Description=Scrcpy - virtual webcam from ADB Device
PartOf=graphical-session.target
StartLimitIntervalSec=5
ConditionUser=!root

[Service]
Type=simple
ExecStart=scrcpy --video-source=camera --no-audio --camera-id=0 --max-size=1000 --camera-ar=sensor --orientation=0 --camera-fps=15 --v4l2-sink=/dev/video0 --no-video-playback --v4l2-buffer=0 --no-clipboard-autosync --no-cleanup --video-codec=h264
Restart=no

StandardOutput=journal
StandardError=journal
SyslogIdentifier=scrcpy-cam
Slice=app.slice