Adding Unknown Video Format V4L2 Support for Infrared Webcam on Linux
Working with an infrared (IR) webcam on a Linux PC can be a bit tricky due to the unknown video format issue. This article will guide you through the process of adding V4L2 (Video for Linux 2) support for an IR webcam on a Linux system.
Understanding the Basics
The Video for Linux (V4L) API is a collection of device drivers and user-space libraries for supporting video capture devices, such as webcams, on Linux systems. V4L2 is the second version of this API and provides improved functionality and performance compared to its predecessor. However, when connecting an IR webcam to a Linux PC, you might encounter issues related to the unknown video format.
Identifying the Problem
When connecting an IR webcam to a Linux PC, you might see logs indicating that the camera is connected, but the video format is unknown. This issue occurs because the webcam's IR video format is not supported by the default V4L2 drivers. To resolve this issue, you need to add support for the unknown video format manually.
Adding Support for Unknown Video Format
To add support for the unknown video format, you need to follow these steps:
- Identify the webcam's video format
- Create a new V4L2 driver for the unknown video format
- Load the new V4L2 driver
Identifying the Webcam's Video Format
To identify the webcam's video format, you can use tools such as v4l2-ctl or guvcview. These tools allow you to view the webcam's properties and settings, including the video format. For example, you can use the following command to view the webcam's video format:
$ v4l2-ctl --allCreating a New V4L2 Driver
Once you have identified the webcam's video format, you can create a new V4L2 driver for the unknown video format. This process involves writing a kernel module that registers the new video format with the V4L2 API. The kernel module should include the following:
- A
struct v4l2_fmtdescstructure that describes the new video format - A
struct v4l2_pix_formatstructure that defines the pixel format, size, and other properties of the new video format - A
struct v4l2_queryctrlstructure that defines the controls for the new video format - A
struct file_operationsstructure that defines the file operations for the new video format
Here is an example of a kernel module that adds support for an unknown video format:
#include
#include
static struct v4l2_fmtdesc fmt = {
.index = 0,
.type = V4L2_BUF_TYPE_VIDEO_CAPTURE,
.description = "Unknown video format",
.pixelformat = V4L2_PIX_FMT_Y16,
.flags = 0,
};
static struct v4l2_pix_format pix = {
.width = 640,
.height = 480,
.pixelformat = V4L2_PIX_FMT_Y16,
.bytesperline = 1280,
.sizeimage = 614400,
.priv = 0,
};
static struct v4l2_queryctrl qctrl = {
.id = V4L2_CID_BRIGHTNESS,
.type = V4L2_CTRL_TYPE_INTEGER,
.name = "Brightness",
.minimum = -100,
.maximum = 100,
.step = 1,
.default_value = 0,
.flags = 0,
};
static const struct v4l2_file_operations fops = {
.owner = THIS_MODULE,
.open = v4l2_fh_open,
.release = v4l2_fh_release,
.read = v4l2_read,
.mmap = v4l2_mmap,
.poll = v4l2_ioctl_poll,
.unlocked_ioctl = video_ioctl2,
};
static int __init init_module(void)
{
int ret;
ret = video_register_device(&video_device, VFL_TYPE_GRABBER, -1);
if (ret < 0)
return ret;
video_set_drvdata(&video_device, NULL);
ret = v4l2_register_ioctl2(video_device.vfd, &fops, V4L2_CAP_VIDEO_CAPTURE);
if (ret < 0)
goto err_video_unregister_device;
ret = v4l2_queryctrl_register(video_device.vfd, &qctrl);
if (ret < 0)
goto err_v4l2_device_unregister;
ret = v4l2_register_format(video_device.vfd, &fmt, 1);
if (ret < 0)
goto err_v4l2_device_unregister;
ret = v4l2_register_format_cap(video_device.vfd, &pix, 1);
if (ret < 0)
goto err_v4l2_device_unregister;
return 0;
err_v4l2_device_unregister:
v4l2_queryctrl_unregister(video_device.vfd, &qctrl);
v4l2_device_unregister(video_device.vfd);
err_video_unregister_device:
video_unregister_device(&video_device);
return ret;
}
static void __exit cleanup_module(void)
{
v4l2_deregister_ioctl2(video_device.vfd);
v4l2_queryctrl_unregister(video_device.vfd, &qctrl);
v4l2_device_unregister(video_device.vfd);
video_unregister_device(&video_device);
} Loading the New V4L2 Driver
Once you have created the new V4L2 driver, you can load it using the modprobe command. For example, you can use the following command to load the new V4L2 driver:
$ sudo modprobe my_new_v4l2_driverAdding support for an unknown video format V4L2 driver for an IR webcam on a Linux system can be a bit challenging, but it is possible. By following the steps outlined in this article, you can add support for the unknown video format and start using your IR webcam on your Linux PC.