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v4l2loopback - a kernel module to create V4L2 loopback devices ============================================================== this module allows you to create "virtual video devices" normal (v4l2) applications will read these devices as if they were ordinary video devices, but the video will not be read from e.g. a capture card but instead it is generated by another application. this allows you for instance to apply apply some nifty video effects on your Skype video... it also allows some more serious things (e.g. I've been using it to add streaming capabilities to an application by the means of hooking GStreamer into the loopback devices). --- NEWS --- to get the main features of each new release, see the NEWS file. you could also have a look at the ChangeLog (which gets automatically generated and might only be of limited use... --- ISSUES --- for current issues, checkout https://github.com/umlaeute/v4l2loopback/issues please use the issue-tracker for reporting any problems --- BUILD --- to build the kernel module run "make". this should give you a file named "v4l2loopback.ko", which is the kernel module --- INSTALL --- to install the module run "make install" (you might have to be 'root' to have all necessary permissions to install the module). if your system has "sudo", do: $ make && sudo make install if your system lacks "sudo", do: $ make $ su (enter root password) # make install # exit --- RUN --- Load the v4l2loopback module as root : # modprobe v4l2loopback using sudo use: $ sudo modprobe v4l2loopback this will create an additional video-device, e.g. /dev/video0 (the number depends on whether you already had video devices on your system), which can be fed by various programs. tested feeders: GStreamer: using the "v4l2sink" element Gem(>=0.93) using the "recordV4L2" plugin in theory most programs capable of _writing to_ a v4l2 device should work. the data sent to the v4l2loopback device can then be read by any v4l2-capable application. you can find a number of scenarios on the wiki at http://github.com/umlaeute/v4l2loopback/wiki --- OPTIONS --- if you need several independent loopback devices, you can pass the "devices" option, when loading the module; e.g. # modprobe v4l2loopback devices=4 will give you 4 loopback devices (e.g. /dev/video1 ... /dev/video5) you can also specify the device IDs manually; e.g. # modprobe v4l2loopback video_nr=3,4,7 will create 3 devices (/dev/video3 /dev/video4 & /dev/video7) --- ATTRIBUTES --- you can set and/or query some per-device attributes via sysfs, in a human readable format. see /sys/devices/virtual/video4linux/video*/ also there are some V4L2 controls that you can list with $ v4l2-ctl -d /dev/video1 -l keep_format(0/1): while set to 1, once negotiated format will be fixed forever, until the setting is set back to 0 sustain_framerate(0/1): if set to 1, nominal device fps will be ensured by means of frame duplication when needed timeout(integer): if >0, will cause a timeout picture (a null frame, by default) to be displayed after (value) msecs of missing input timeout_image_io(0/1): if set to 1, the next opener will write to timeout frame buffer --- FORCING FPS --- $ v4l2loopback-ctl set-fps 25 /dev/video0 or $ echo '@100' | sudo tee /sys/devices/virtual/video4linux/video0/format --- FORCING A GSTREAMER (0.10) CAPS --- $ v4l2loopback-ctl set-caps "video/x-raw-yuv, width=640, height=480" /dev/video0 --- SETTING STREAM TIMEOUT --- $ v4l2-ctl -d /dev/video0 -c timeout=3000 (will output null frames by default) $ v4l2loopback-ctl set-timeout-image service-unavailable.png /dev/video0 this currently requires GStreamer 0.10 installed --- KERNELs --- the original module has been developed for linux-2.6.28; i don't have a system with such an old kernel anymore, so i don't know whether it still works. further development has been done mainly on linux-2.6.32 and linux-2.6.35, with newer kernels being continually tested as they enter debian. support: <= 2.6.27 definitely will NOT work 2.6.28 - 2.6.31 may work (seems to compile but i cannot test) >= 2.6.32 should work >= 3.0.0 should work as well --- DISTRIBUTIONS --- v4l2loopack is now (2010-10-13) available as a Debian-package. This means, that it is also part of Debian-derived distributions, including Ubuntu (starting with natty). The most convenient way is to install the package "v4l2loopback-dkms". This should automatically build and install the module for your current kernel (provided you have the matching kernel-headers installed). Another option is to install the "v4l2loopback-source" package. In this case you should be able to simply do (as root): # aptitude install v4l2loopback-source module-assistant # module-assistant auto-install v4l2loopback-source --- DOWNLOAD --- the most up-to-date version of this module can be found at http://github.com/umlaeute/v4l2loopback/. --- LICENSE/COPYING --- Copyright (c) 2010-2012 IOhannes m zmoelnig <firstname.lastname@example.org> Copyright (c) 2012 Anton Novikov (email@example.com) Copyright (c) 2011 Stefan Diewald (firstname.lastname@example.org) Copyright (c) 2010 Scott Maines <email@example.com> Copyright (c) 2009 Gorinich Zmey Copyright (c) 2005-2009 Vasily Levin This package is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This package is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.