.. Permission is granted to copy, distribute and/or modify this
.. document under the terms of the GNU Free Documentation License,
.. Version 1.1 or any later version published by the Free Software
.. Foundation, with no Invariant Sections, no Front-Cover Texts
.. and no Back-Cover Texts. A copy of the license is included at
.. Documentation/media/uapi/fdl-appendix.rst.
..
.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections

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;
    }