V4L2 output

Nageru has (in addition to the regular HDMI/SDI output) support for output to Linux’ Video4Linux API (also known as V4L2, or just V4L). This is intended for one specific purpose, namely using Nageru as a camera/mixer for input to a video conference, such at Jitsi, Google Meet or similar—it may not be all that suitable for an actual output, since it does not carry audio (and does not synchronize to any V4L clock).

To use it as an input, you will first need to install v4l2loopback, which turns V4L outputs into V4L inputs. If you are on Debian or Ubuntu, the following should suffice to install:

sudo apt install v4l2loopback-dkms

You will also need to load and configure the module, using a command line such as:

sudo modprobe v4l2loopback video_nr=2 card_label='Nageru loopback' max_width=1280 max_height=720 exclusive_caps=1

The exclusive_caps=1 parameter is so that once you start outputting, the virtual card will appear only as an input card to other V4L clients; in particular, Google Chrome needs this, or the card will not show up. However, this means that you will need to start Nageru output before trying to use it in the browser.

Finally, you can start Nageru as usual with the –v4l-output flag, outputting to the device you just created:

nageru --v4l-output /dev/video2

Nageru should then show up as a device in your browser or videoconferencing client.

V4L output is in addition to any other output you may have (whether stream output, HDMI/SDI output, or both), and can only be configured from the command line. It does not control the master clock, is always 4:2:0; and does not include audio.