vcam: Virtual camera device driver for Linux

This Linux module implements a simplified virtual V4L2 compatible camera device driver with raw framebuffer input.

Prerequisite

The following packages must be installed before building vcam.

In order to compile the kernel driver successfully, package versions of currently used kernel, kernel-devel and kernel-headers need to be matched.

$ sudo apt install linux-headers-$(uname -r)

Since vcam is built with V4L2 (Video4Linux, second version), v4l-utils is necessary for retrieving more information and function validation:

$ sudo apt install v4l-utils

Build and Run

After running make, you should be able to generate the following files:

• vcam.ko - Linux kernel module;
• vcam-util - Sample utility to configure virtual camera device(s);

Before loading this kernel module, you have to satisfy its dependency:

$ sudo modprobe -a videobuf2_vmalloc videobuf2_v4l2

The module can be loaded to Linux kernel by runnning the command:

$ sudo insmod vcam.ko

Expectedly, three device nodes will be created in /dev:

• videoX - V4L2 device;
• vcamctl - Control device for virtual camera(s), used by control utility vcam-util;
• fbX - controlling framebuffer device;

In /dev directory, device file fbX will be created.

The device is initially configured to process 640x480 RGB24 image format. By writing 640x480 RGB24 raw frame data to /dev/fbX file the resulting video stream will appear on corresponding /dev/videoX V4L2 device(s).

Run vcam-util --help for more information about how to configure, add or remove virtual camera devices. e.g. list all available virtual camera device(s):

$ sudo ./vcam-util -l

You should get:

Available virtual V4L2 compatible devices:
1. fbX(640,480,rgb24) -> /dev/video0

You can use this command to check if the driver is ok:

$ sudo v4l2-compliance -d /dev/videoX -f

It will return a bunch of test lines, with 0 failed and 0 warnings at the end.

You can check if all configured formats and emulated controls are ok with this command:

$ sudo v4l2-ctl -d /dev/videoX --all

You will get information as following:

Driver Info:
    Driver name   : vcam
    Card type     : vcam
    Bus info      : platform: virtual
    Driver version: 4.15.18
    Capabilities  : 0x85200001
        Video Capture
        Read/Write
        Streaming
        Extended Pix Format
        Device Capabilities

You can check framebuffer format with this command:

$ sudo fbset -fb /dev/fbX --info

You will get information as following:

mode "640x480"
    geometry 640 480 640 480 24
    timings 0 0 0 0 0 0 0
    rgba 8/0,8/8,8/16,0/0
endmode

Frame buffer device information:
    Name        : vcamfb
    Address     : 0xffffa293438ed000
    Size        : 921600
    Type        : PACKED PIXELS
    Visual      : TRUECOLOR

Available parameters for vcam kernel module:

• devices_max - Maximal number of devices. The default is 8.
• create_devices - Number of devices to be created during initialization. The default is 1.
• allow_pix_conversion - Allow pixel format conversion from RGB24 to YUYV. The default is OFF.
• allow_scaling - Allow image scaling from 480p to 720p. The default is OFF.
• allow_cropping - Allow image cropping in Four-Thirds system. The default is OFF.

When you load a module using insmod command, you can supply the parameters as key=value pairs for example:

$ sudo insmod vcam.ko allow_pix_conversion=1

Related Projects

• akvcam
• v4l2loopback
• vivid: The Virtual Video Test Driver

License

vcam is released under the MIT License. Use of this source code is governed by a MIT License that can be found in the LICENSE file.