Output all video devices, capabilities, frame sizes and related framerates on Linux using V4L2

README.md

Output all video devices, capabilities, frame sizes and related framerates on Linux using V4L2

Compile it using

clang -o print_devices print_devices.c

Example output

Driver:'uvcvideo', Card:'USB 2.0 Camera', Device: '/dev/video0', buf_info:'usb-xhci-hcd.2.auto-1.2', version:264486, capabilities:0x84200001}
Pixel format: 'YUYV', Description = 'YUYV 4:2:2'
Size: 640x480
  0.030s (33.000 fps)
  0.067s (15.000 fps)
Size: 1280x720
  0.100s (10.000 fps)
Size: 640x360
  0.030s (33.000 fps)
  0.067s (15.000 fps)
Size: 544x288
  0.030s (33.000 fps)
  0.067s (15.000 fps)
Size: 432x240
  0.030s (33.000 fps)
  0.067s (15.000 fps)
...

print_devices.c

#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <string.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/videodev2.h>

static int v4l2_is_v4l_device(const char *name)
{
 return !strncmp(name, "video", 5) ||
           !strncmp(name, "radio", 5) ||
           !strncmp(name, "vbi", 3) ||
           !strncmp(name, "v4l-subdev", 10); 
}

static int v4l2_get_device_list()
{
  int fd, ret;
  DIR *dir;
  struct dirent *entry;

  struct v4l2_capability cap;
  struct v4l2_fmtdesc fmt;
  struct v4l2_frmsizeenum frmsize;
  struct v4l2_frmivalenum frmival;

  dir = opendir("/dev");
  if (!dir) {
    fprintf(stderr, "Could not open /dev directory!\n");
    return 1;
  }

  while ((entry = readdir(dir))) {
    char device_name[256];

    if (!v4l2_is_v4l_device(entry->d_name)) {
      continue;
    }

    snprintf(device_name, sizeof(device_name), "/dev/%s", entry->d_name);
    
    if ((fd = open(device_name, O_RDONLY)) == -1) {
      fprintf(stderr, "Cannot open device %s\n", device_name);
      return 1;
    }

    if (ioctl(fd, VIDIOC_QUERYCAP, &cap) == -1) {
      fprintf(stderr, "Cannot get capabilities!\n");
      return 1;
    }

    printf("Driver:'%s', Card:'%s', Device: '%s', buf_info:'%s', version:%d, capabilities:0x%x}\n", cap.driver, cap.card, device_name, cap.bus_info, cap.version, cap.capabilities);	

    fmt.index = 0;
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    while ((ret = ioctl(fd, VIDIOC_ENUM_FMT, &fmt)) >= 0) {
      fprintf(stderr, "Pixel format: '%c%c%c%c', Description = '%s'\n", fmt.pixelformat & 0xFF, (fmt.pixelformat >> 8) & 0xFF, (fmt.pixelformat >> 16) & 0xFF, (fmt.pixelformat >> 24) & 0xFF, fmt.description);

      frmsize.pixel_format = fmt.pixelformat;
      frmsize.index = 0;

      while ((ret = ioctl(fd, VIDIOC_ENUM_FRAMESIZES, &frmsize)) >= 0) {
        if (frmsize.type == V4L2_FRMSIZE_TYPE_DISCRETE) {
          fprintf(stderr, "Size: %dx%d\n", frmsize.discrete.width, frmsize.discrete.height);
          frmival.index = 0;
          frmival.pixel_format = fmt.pixelformat;
          frmival.width = frmsize.discrete.width;
          frmival.height = frmsize.discrete.height;
          while ((ret = ioctl(fd, VIDIOC_ENUM_FRAMEINTERVALS, &frmival)) >= 0) {
            if (frmival.type == V4L2_FRMIVAL_TYPE_DISCRETE) {
              char sec[100], fps[100];
              sprintf(sec, "%.3f", (1.0 * frmival.discrete.numerator) / frmival.discrete.denominator);
              sprintf(fps, "%.3f", (1.0 * frmival.discrete.denominator) / frmival.discrete.numerator);
              fprintf(stderr, "  %ss (%s fps)\n", sec, fps);
            }
            frmival.index++;
          }
        }
        frmsize.index++;
      }

      printf("\n");
      fmt.index++;
    }

  }

  return 0;
}

int main() {
  int ret;
  if ((ret = v4l2_get_device_list()) != 0) {
    fprintf(stderr, "Error\n");
  }

  return 0;
}