list_cams.c

// list_cams.c : list webcams, their pixel-formats & resolutions
#define _GNU_SOURCE
#include <stdio.h>
#include <fcntl.h>
#include <linux/videodev2.h>
#include <dirent.h>
#include <string.h>
#include <unistd.h>
#include <sys/ioctl.h>

static void show_caps(int fd) {
    struct v4l2_capability cap;
    if (ioctl(fd, VIDIOC_QUERYCAP, &cap) == -1) return;
    printf("  Driver: %-16s  Card: %s\n", cap.driver, cap.card);

    struct v4l2_fmtdesc fmtd = { .index = 0, .type = V4L2_BUF_TYPE_VIDEO_CAPTURE };
    while (!ioctl(fd, VIDIOC_ENUM_FMT, &fmtd)) {
        printf("    pixfmt: %c%c%c%c  %s\n",
               fmtd.pixelformat & 0xff, (fmtd.pixelformat >> 8) & 0xff,
               (fmtd.pixelformat >> 16) & 0xff, (fmtd.pixelformat >> 24) & 0xff,
               fmtd.description);
        struct v4l2_frmsizeenum sz = { .pixel_format = fmtd.pixelformat, .index = 0 };
        while (!ioctl(fd, VIDIOC_ENUM_FRAMESIZES, &sz)) {
            if (sz.type == V4L2_FRMSIZE_TYPE_DISCRETE)
                printf("      %ux%u\n", sz.discrete.width, sz.discrete.height);
            sz.index++;
        }
        fmtd.index++;
    }
}

int main(void) {
    DIR *d = opendir("/dev");
    struct dirent *ent;
    if (!d) { perror("opendir"); return 1; }
    while ((ent = readdir(d))) {
        if (strncmp(ent->d_name, "video", 5) == 0) {
            char path[64]; snprintf(path, sizeof(path), "/dev/%s", ent->d_name);
            int fd = open(path, O_RDWR);
            if (fd == -1) continue;
            printf("%s:\n", path);
            show_caps(fd);
            close(fd);
        }
    }
    closedir(d);
    return 0;
}