v4l2grab.c.rst

  1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
  2.. c:namespace:: V4L
  3
  4file: media/v4l/v4l2grab.c
  5==========================
  6
  7.. code-block:: c
  8
  9    /* V4L2 video picture grabber
 10       Copyright (C) 2009 Mauro Carvalho Chehab <mchehab@kernel.org>
 11
 12       This program is free software; you can redistribute it and/or modify
 13       it under the terms of the GNU General Public License as published by
 14       the Free Software Foundation version 2 of the License.
 15
 16       This program is distributed in the hope that it will be useful,
 17       but WITHOUT ANY WARRANTY; without even the implied warranty of
 18       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 19       GNU General Public License for more details.
 20     */
 21
 22    #include <stdio.h>
 23    #include <stdlib.h>
 24    #include <string.h>
 25    #include <fcntl.h>
 26    #include <errno.h>
 27    #include <sys/ioctl.h>
 28    #include <sys/types.h>
 29    #include <sys/time.h>
 30    #include <sys/mman.h>
 31    #include <linux/videodev2.h>
 32    #include "../libv4l/include/libv4l2.h"
 33
 34    #define CLEAR(x) memset(&(x), 0, sizeof(x))
 35
 36    struct buffer {
 37	    void   *start;
 38	    size_t length;
 39    };
 40
 41    static void xioctl(int fh, int request, void *arg)
 42    {
 43	    int r;
 44
 45	    do {
 46		    r = v4l2_ioctl(fh, request, arg);
 47	    } while (r == -1 && ((errno == EINTR) || (errno == EAGAIN)));
 48
 49	    if (r == -1) {
 50		    fprintf(stderr, "error %d, %s\n", errno, strerror(errno));
 51		    exit(EXIT_FAILURE);
 52	    }
 53    }
 54
 55    int main(int argc, char **argv)
 56    {
 57	    struct v4l2_format              fmt;
 58	    struct v4l2_buffer              buf;
 59	    struct v4l2_requestbuffers      req;
 60	    enum v4l2_buf_type              type;
 61	    fd_set                          fds;
 62	    struct timeval                  tv;
 63	    int                             r, fd = -1;
 64	    unsigned int                    i, n_buffers;
 65	    char                            *dev_name = "/dev/video0";
 66	    char                            out_name[256];
 67	    FILE                            *fout;
 68	    struct buffer                   *buffers;
 69
 70	    fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);
 71	    if (fd < 0) {
 72		    perror("Cannot open device");
 73		    exit(EXIT_FAILURE);
 74	    }
 75
 76	    CLEAR(fmt);
 77	    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 78	    fmt.fmt.pix.width       = 640;
 79	    fmt.fmt.pix.height      = 480;
 80	    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_RGB24;
 81	    fmt.fmt.pix.field       = V4L2_FIELD_INTERLACED;
 82	    xioctl(fd, VIDIOC_S_FMT, &fmt);
 83	    if (fmt.fmt.pix.pixelformat != V4L2_PIX_FMT_RGB24) {
 84		    printf("Libv4l didn't accept RGB24 format. Can't proceed.\n");
 85		    exit(EXIT_FAILURE);
 86	    }
 87	    if ((fmt.fmt.pix.width != 640) || (fmt.fmt.pix.height != 480))
 88		    printf("Warning: driver is sending image at %dx%d\n",
 89			    fmt.fmt.pix.width, fmt.fmt.pix.height);
 90
 91	    CLEAR(req);
 92	    req.count = 2;
 93	    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 94	    req.memory = V4L2_MEMORY_MMAP;
 95	    xioctl(fd, VIDIOC_REQBUFS, &req);
 96
 97	    buffers = calloc(req.count, sizeof(*buffers));
 98	    for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
 99		    CLEAR(buf);
100
101		    buf.type        = V4L2_BUF_TYPE_VIDEO_CAPTURE;
102		    buf.memory      = V4L2_MEMORY_MMAP;
103		    buf.index       = n_buffers;
104
105		    xioctl(fd, VIDIOC_QUERYBUF, &buf);
106
107		    buffers[n_buffers].length = buf.length;
108		    buffers[n_buffers].start = v4l2_mmap(NULL, buf.length,
109				  PROT_READ | PROT_WRITE, MAP_SHARED,
110				  fd, buf.m.offset);
111
112		    if (MAP_FAILED == buffers[n_buffers].start) {
113			    perror("mmap");
114			    exit(EXIT_FAILURE);
115		    }
116	    }
117
118	    for (i = 0; i < n_buffers; ++i) {
119		    CLEAR(buf);
120		    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
121		    buf.memory = V4L2_MEMORY_MMAP;
122		    buf.index = i;
123		    xioctl(fd, VIDIOC_QBUF, &buf);
124	    }
125	    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
126
127	    xioctl(fd, VIDIOC_STREAMON, &type);
128	    for (i = 0; i < 20; i++) {
129		    do {
130			    FD_ZERO(&fds);
131			    FD_SET(fd, &fds);
132
133			    /* Timeout. */
134			    tv.tv_sec = 2;
135			    tv.tv_usec = 0;
136
137			    r = select(fd + 1, &fds, NULL, NULL, &tv);
138		    } while ((r == -1 && (errno == EINTR)));
139		    if (r == -1) {
140			    perror("select");
141			    return errno;
142		    }
143
144		    CLEAR(buf);
145		    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
146		    buf.memory = V4L2_MEMORY_MMAP;
147		    xioctl(fd, VIDIOC_DQBUF, &buf);
148
149		    sprintf(out_name, "out%03d.ppm", i);
150		    fout = fopen(out_name, "w");
151		    if (!fout) {
152			    perror("Cannot open image");
153			    exit(EXIT_FAILURE);
154		    }
155		    fprintf(fout, "P6\n%d %d 255\n",
156			    fmt.fmt.pix.width, fmt.fmt.pix.height);
157		    fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
158		    fclose(fout);
159
160		    xioctl(fd, VIDIOC_QBUF, &buf);
161	    }
162
163	    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
164	    xioctl(fd, VIDIOC_STREAMOFF, &type);
165	    for (i = 0; i < n_buffers; ++i)
166		    v4l2_munmap(buffers[i].start, buffers[i].length);
167	    v4l2_close(fd);
168
169	    return 0;
170    }