V4l2loopback

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v4l2loopback provides a way for applications to act as a capture card would, looping back video output as input for use in other applications.

Installation

Kernel

KERNEL Enable support for V4L

Device Drivers  --->
   Multimedia support --->
      Media drivers --->
         <*> V4L test drivers

USE flags

USE flags for media-video/v4l2loopback v4l2 loopback device whose output is its own input

dist-kernel	Enable subslot rebuilds on Distribution Kernel upgrades
examples	Install examples, usually source code
modules-compress	Install compressed kernel modules (if kernel config enables module compression)
modules-sign	Cryptographically sign installed kernel modules (requires CONFIG_MODULE_SIG=y in the kernel)
strip	Allow symbol stripping to be performed by the ebuild for special files

Data provided by the Gentoo Package Database · Last update: 2024-03-23 06:35 More information about USE flags

Emerge

root #emerge --ask media-video/v4l2loopback

Usage

Invocation

user $v4l2loopback-ctl -h

usage: v4l2loopback-ctl [general commands]


 general commands
 ================
	-v/--version : print version and exit
	-h/-?/--help : print this help and exit
	 add {<flags>} [<outputdevice> [<capturedevice>]]

	 delete <device>

	 list {<flags>}

	 query {<flags>} <device>

	 set-fps <device> <fps>

	 get-fps <device>

	 set-caps <device> <caps>

	 get-caps <device>

	 set-timeout-image {<flags>} <device> <image>



 adding devices ('add')
 ======================
	v4l2loopback-ctl add {<flags>} [<outputdevice> [<capturedevice>]]

   <flags>	any of the following flags may be present
	 -n/--name <name>        : pretty name for the device
	 --min-width <w>         : minimum allowed frame width
	 -w/--max-width <w>      : maximum allowed frame width
	 --min-height <w>        : minimum allowed frame height
	 -h/--max-height <h>     : maximum allowed frame height
	 -x/--exclusive-caps <x> : whether to announce OUTPUT/CAPTURE capabilities exclusively
	 -b/--buffers <num>      : buffers to queue
	 -o/--max-openers <num>  : maximum allowed concurrent openers
	 -v/--verbose            : verbose mode (print properties of device after successfully creating it)
	 -?/--help               : print this help and exit

  <outputdevice>	if given, create a specific device (otherwise just create a free one).
          	either specify a device name (e.g. '/dev/video1') or a device number ('1').
  <capturedevice>	if given, use separate output & capture devices (otherwise they are the same).


 deleting devices ('delete')
 ===========================
	v4l2loopback-ctl delete <device>

  <device>	can be given one more more times (to delete multiple devices at once).
          	either specify a device name (e.g. '/dev/video1') or a device number ('1').


 listing devices ('list')
 ========================
	v4l2loopback-ctl list {<flags>}

   <flags>	any of the following flags may be present
	 -e/--escape             : escape control-characters in (device) names
	 -h/--help               : print this help and exit

         	list all available loopback-devices


 querying devices ('query')
 ==========================
	v4l2loopback-ctl query {<flags>} <device>

   <flags>	any of the following flags may be present
	 -e/--escape             : escape control-characters in (device) names
	 -h/--help               : print this help and exit

  <device>	can be given one more more times (to query multiple devices at once).
         	either specify a device name (e.g. '/dev/video1') or a device number ('1').


 setting framerate ('set-fps')
 =============================
	v4l2loopback-ctl set-fps <device> <fps>

  <device>	either specify a device name (e.g. '/dev/video1') or a device number ('1').
     <fps>	frames per second, either as integer ('30') or fraction ('50/2').


 getting framerate ('get-fps')
 =============================
	v4l2loopback-ctl get-fps <device>



 setting capabilities ('set-caps')
 =================================
	v4l2loopback-ctl set-caps <device> <caps>

  <device>	either specify a device name (e.g. '/dev/video1') or a device number ('1').
    <caps>	format specification as '<fourcc>:<width>x<height>@<fps>' (e.g. 'UYVY:1024x768@60/1')



 getting capabilities ('get-caps')
 =================================
	v4l2loopback-ctl get-caps <device>



 setting timeout image ('set-timeout-image')
 ===========================================
	v4l2loopback-ctl set-timeout-image {<flags>} <device> <image>

   <flags>	any of the following flags may be present
	 -t/--timeout <timeout>  : timeout (in ms)
	 -v/--verbose            : raise verbosity (print what is being done)
	 -h/--help               : print this help and exit

  <device>	either specify a device name (e.g. '/dev/video1') or a device number ('1').
   <image>	image file

Removal

root #emerge --ask --depclean --verbose media-video/v4l2loopback

Troubleshooting

Module Not Found

You may see an error message like the one below when loading the module.

root #modprobe v4l2loopback

modprobe: FATAL: Module v4l2loopback not found in directory /lib/modules/6.6.21-gentoo

First, ensure you are booted into the correct kernel.

user $uname -a

user $ eselect kernel list

If these do not match up, you may need to update your bootloader config. For GRUB:

root #grub-mkconfig -o /boot/grub/grub.cfg

You may also need to rebuild your kernel modules.

root #emerge --ask @module-rebuild

External resources

• v4l2loopback (Arch Linux Wiki)