xref: /kernel/linux/linux-6.6/Documentation/userspace-api/media/v4l/v4l2grab.c.rst (revision 62306a36)

.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later

file: media/v4l/v4l2grab.c
==========================

.. code-block:: c

    /* V4L2 video picture grabber
       Copyright (C) 2009 Mauro Carvalho Chehab <mchehab@kernel.org>

       This program is free software; you can redistribute it and/or modify
       it under the terms of the GNU General Public License as published by
       the Free Software Foundation version 2 of the License.

       This program is distributed in the hope that it will be useful,
       but WITHOUT ANY WARRANTY; without even the implied warranty of
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
       GNU General Public License for more details.
     */

    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <fcntl.h>
    #include <errno.h>
    #include <sys/ioctl.h>
    #include <sys/types.h>
    #include <sys/time.h>
    #include <sys/mman.h>
    #include <linux/videodev2.h>
    #include "../libv4l/include/libv4l2.h"

    #define CLEAR(x) memset(&(x), 0, sizeof(x))

    struct buffer {
	    void   *start;
	    size_t length;
    };

    static void xioctl(int fh, int request, void *arg)
    {
	    int r;

	    do {
		    r = v4l2_ioctl(fh, request, arg);
	    } while (r == -1 && ((errno == EINTR) || (errno == EAGAIN)));

	    if (r == -1) {
		    fprintf(stderr, "error %d, %s\n", errno, strerror(errno));
		    exit(EXIT_FAILURE);
	    }
    }

    int main(int argc, char **argv)
    {
	    struct v4l2_format              fmt;
	    struct v4l2_buffer              buf;
	    struct v4l2_requestbuffers      req;
	    enum v4l2_buf_type              type;
	    fd_set                          fds;
	    struct timeval                  tv;
	    int                             r, fd = -1;
	    unsigned int                    i, n_buffers;
	    char                            *dev_name = "/dev/video0";
	    char                            out_name[256];
	    FILE                            *fout;
	    struct buffer                   *buffers;

	    fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);
	    if (fd < 0) {
		    perror("Cannot open device");
		    exit(EXIT_FAILURE);
	    }

	    CLEAR(fmt);
	    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	    fmt.fmt.pix.width       = 640;
	    fmt.fmt.pix.height      = 480;
	    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_RGB24;
	    fmt.fmt.pix.field       = V4L2_FIELD_INTERLACED;
	    xioctl(fd, VIDIOC_S_FMT, &fmt);
	    if (fmt.fmt.pix.pixelformat != V4L2_PIX_FMT_RGB24) {
		    printf("Libv4l didn't accept RGB24 format. Can't proceed.\n");
		    exit(EXIT_FAILURE);
	    }
	    if ((fmt.fmt.pix.width != 640) || (fmt.fmt.pix.height != 480))
		    printf("Warning: driver is sending image at %dx%d\n",
			    fmt.fmt.pix.width, fmt.fmt.pix.height);

	    CLEAR(req);
	    req.count = 2;
	    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	    req.memory = V4L2_MEMORY_MMAP;
	    xioctl(fd, VIDIOC_REQBUFS, &req);

	    buffers = calloc(req.count, sizeof(*buffers));
	    for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
		    CLEAR(buf);

		    buf.type        = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		    buf.memory      = V4L2_MEMORY_MMAP;
		    buf.index       = n_buffers;

		    xioctl(fd, VIDIOC_QUERYBUF, &buf);

		    buffers[n_buffers].length = buf.length;
		    buffers[n_buffers].start = v4l2_mmap(NULL, buf.length,
				  PROT_READ | PROT_WRITE, MAP_SHARED,
				  fd, buf.m.offset);

		    if (MAP_FAILED == buffers[n_buffers].start) {
			    perror("mmap");
			    exit(EXIT_FAILURE);
		    }
	    }

	    for (i = 0; i < n_buffers; ++i) {
		    CLEAR(buf);
		    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		    buf.memory = V4L2_MEMORY_MMAP;
		    buf.index = i;
		    xioctl(fd, VIDIOC_QBUF, &buf);
	    }
	    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

	    xioctl(fd, VIDIOC_STREAMON, &type);
	    for (i = 0; i < 20; i++) {
		    do {
			    FD_ZERO(&fds);
			    FD_SET(fd, &fds);

			    /* Timeout. */
			    tv.tv_sec = 2;
			    tv.tv_usec = 0;

			    r = select(fd + 1, &fds, NULL, NULL, &tv);
		    } while ((r == -1 && (errno == EINTR)));
		    if (r == -1) {
			    perror("select");
			    return errno;
		    }

		    CLEAR(buf);
		    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		    buf.memory = V4L2_MEMORY_MMAP;
		    xioctl(fd, VIDIOC_DQBUF, &buf);

		    sprintf(out_name, "out%03d.ppm", i);
		    fout = fopen(out_name, "w");
		    if (!fout) {
			    perror("Cannot open image");
			    exit(EXIT_FAILURE);
		    }
		    fprintf(fout, "P6\n%d %d 255\n",
			    fmt.fmt.pix.width, fmt.fmt.pix.height);
		    fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
		    fclose(fout);

		    xioctl(fd, VIDIOC_QBUF, &buf);
	    }

	    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	    xioctl(fd, VIDIOC_STREAMOFF, &type);
	    for (i = 0; i < n_buffers; ++i)
		    v4l2_munmap(buffers[i].start, buffers[i].length);
	    v4l2_close(fd);

	    return 0;
    }