Documentation/media/uapi/v4l/capture.c.rst

   1 .. Permission is granted to copy, distribute and/or modify this
   2 .. document under the terms of the GNU Free Documentation License,
   3 .. Version 1.1 or any later version published by the Free Software
   4 .. Foundation, with no Invariant Sections, no Front-Cover Texts
   5 .. and no Back-Cover Texts. A copy of the license is included at
   6 .. Documentation/media/uapi/fdl-appendix.rst.
   7 ..
   8 .. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
   9
  10 file: media/v4l/capture.c
  11 =========================
  12
  13 .. code-block:: c
  14
  15     /*
  16      *  V4L2 video capture example
  17      *
  18      *  This program can be used and distributed without restrictions.
  19      *
  20      *      This program is provided with the V4L2 API
  21      * see https://linuxtv.org/docs.php for more information
  22      */
  23
  24     #include <stdio.h>
  25     #include <stdlib.h>
  26     #include <string.h>
  27     #include <assert.h>
  28
  29     #include <getopt.h>             /* getopt_long() */
  30
  31     #include <fcntl.h>              /* low-level i/o */
  32     #include <unistd.h>
  33     #include <errno.h>
  34     #include <sys/stat.h>
  35     #include <sys/types.h>
  36     #include <sys/time.h>
  37     #include <sys/mman.h>
  38     #include <sys/ioctl.h>
  39
  40     #include <linux/videodev2.h>
  41
  42     #define CLEAR(x) memset(&(x), 0, sizeof(x))
  43
  44     enum io_method {
  45             IO_METHOD_READ,
  46             IO_METHOD_MMAP,
  47             IO_METHOD_USERPTR,
  48     };
  49
  50     struct buffer {
  51             void   *start;
  52             size_t  length;
  53     };
  54
  55     static char            *dev_name;
  56     static enum io_method   io = IO_METHOD_MMAP;
  57     static int              fd = -1;
  58     struct buffer          *buffers;
  59     static unsigned int     n_buffers;
  60     static int              out_buf;
  61     static int              force_format;
  62     static int              frame_count = 70;
  63
  64     static void errno_exit(const char *s)
  65     {
  66             fprintf(stderr, "%s error %d, %s\\n", s, errno, strerror(errno));
  67             exit(EXIT_FAILURE);
  68     }
  69
  70     static int xioctl(int fh, int request, void *arg)
  71     {
  72             int r;
  73
  74             do {
  75                     r = ioctl(fh, request, arg);
  76             } while (-1 == r && EINTR == errno);
  77
  78             return r;
  79     }
  80
  81     static void process_image(const void *p, int size)
  82     {
  83             if (out_buf)
  84                     fwrite(p, size, 1, stdout);
  85
  86             fflush(stderr);
  87             fprintf(stderr, ".");
  88             fflush(stdout);
  89     }
  90
  91     static int read_frame(void)
  92     {
  93             struct v4l2_buffer buf;
  94             unsigned int i;
  95
  96             switch (io) {
  97             case IO_METHOD_READ:
  98                     if (-1 == read(fd, buffers[0].start, buffers[0].length)) {
  99                             switch (errno) {
 100                             case EAGAIN:
 101                                     return 0;
 102
 103                             case EIO:
 104                                     /* Could ignore EIO, see spec. */
 105
 106                                     /* fall through */
 107
 108                             default:
 109                                     errno_exit("read");
 110                             }
 111                     }
 112
 113                     process_image(buffers[0].start, buffers[0].length);
 114                     break;
 115
 116             case IO_METHOD_MMAP:
 117                     CLEAR(buf);
 118
 119                     buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 120                     buf.memory = V4L2_MEMORY_MMAP;
 121
 122                     if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
 123                             switch (errno) {
 124                             case EAGAIN:
 125                                     return 0;
 126
 127                             case EIO:
 128                                     /* Could ignore EIO, see spec. */
 129
 130                                     /* fall through */
 131
 132                             default:
 133                                     errno_exit("VIDIOC_DQBUF");
 134                             }
 135                     }
 136
 137                     assert(buf.index < n_buffers);
 138
 139                     process_image(buffers[buf.index].start, buf.bytesused);
 140
 141                     if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
 142                             errno_exit("VIDIOC_QBUF");
 143                     break;
 144
 145             case IO_METHOD_USERPTR:
 146                     CLEAR(buf);
 147
 148                     buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 149                     buf.memory = V4L2_MEMORY_USERPTR;
 150
 151                     if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
 152                             switch (errno) {
 153                             case EAGAIN:
 154                                     return 0;
 155
 156                             case EIO:
 157                                     /* Could ignore EIO, see spec. */
 158
 159                                     /* fall through */
 160
 161                             default:
 162                                     errno_exit("VIDIOC_DQBUF");
 163                             }
 164                     }
 165
 166                     for (i = 0; i < n_buffers; ++i)
 167                             if (buf.m.userptr == (unsigned long)buffers[i].start
 168                                 && buf.length == buffers[i].length)
 169                                     break;
 170
 171                     assert(i < n_buffers);
 172
 173                     process_image((void *)buf.m.userptr, buf.bytesused);
 174
 175                     if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
 176                             errno_exit("VIDIOC_QBUF");
 177                     break;
 178             }
 179
 180             return 1;
 181     }
 182
 183     static void mainloop(void)
 184     {
 185             unsigned int count;
 186
 187             count = frame_count;
 188
 189             while (count-- > 0) {
 190                     for (;;) {
 191                             fd_set fds;
 192                             struct timeval tv;
 193                             int r;
 194
 195                             FD_ZERO(&fds);
 196                             FD_SET(fd, &fds);
 197
 198                             /* Timeout. */
 199                             tv.tv_sec = 2;
 200                             tv.tv_usec = 0;
 201
 202                             r = select(fd + 1, &fds, NULL, NULL, &tv);
 203
 204                             if (-1 == r) {
 205                                     if (EINTR == errno)
 206                                             continue;
 207                                     errno_exit("select");
 208                             }
 209
 210                             if (0 == r) {
 211                                     fprintf(stderr, "select timeout\\n");
 212                                     exit(EXIT_FAILURE);
 213                             }
 214
 215                             if (read_frame())
 216                                     break;
 217                             /* EAGAIN - continue select loop. */
 218                     }
 219             }
 220     }
 221
 222     static void stop_capturing(void)
 223     {
 224             enum v4l2_buf_type type;
 225
 226             switch (io) {
 227             case IO_METHOD_READ:
 228                     /* Nothing to do. */
 229                     break;
 230
 231             case IO_METHOD_MMAP:
 232             case IO_METHOD_USERPTR:
 233                     type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 234                     if (-1 == xioctl(fd, VIDIOC_STREAMOFF, &type))
 235                             errno_exit("VIDIOC_STREAMOFF");
 236                     break;
 237             }
 238     }
 239
 240     static void start_capturing(void)
 241     {
 242             unsigned int i;
 243             enum v4l2_buf_type type;
 244
 245             switch (io) {
 246             case IO_METHOD_READ:
 247                     /* Nothing to do. */
 248                     break;
 249
 250             case IO_METHOD_MMAP:
 251                     for (i = 0; i < n_buffers; ++i) {
 252                             struct v4l2_buffer buf;
 253
 254                             CLEAR(buf);
 255                             buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 256                             buf.memory = V4L2_MEMORY_MMAP;
 257                             buf.index = i;
 258
 259                             if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
 260                                     errno_exit("VIDIOC_QBUF");
 261                     }
 262                     type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 263                     if (-1 == xioctl(fd, VIDIOC_STREAMON, &type))
 264                             errno_exit("VIDIOC_STREAMON");
 265                     break;
 266
 267             case IO_METHOD_USERPTR:
 268                     for (i = 0; i < n_buffers; ++i) {
 269                             struct v4l2_buffer buf;
 270
 271                             CLEAR(buf);
 272                             buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 273                             buf.memory = V4L2_MEMORY_USERPTR;
 274                             buf.index = i;
 275                             buf.m.userptr = (unsigned long)buffers[i].start;
 276                             buf.length = buffers[i].length;
 277
 278                             if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
 279                                     errno_exit("VIDIOC_QBUF");
 280                     }
 281                     type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 282                     if (-1 == xioctl(fd, VIDIOC_STREAMON, &type))
 283                             errno_exit("VIDIOC_STREAMON");
 284                     break;
 285             }
 286     }
 287
 288     static void uninit_device(void)
 289     {
 290             unsigned int i;
 291
 292             switch (io) {
 293             case IO_METHOD_READ:
 294                     free(buffers[0].start);
 295                     break;
 296
 297             case IO_METHOD_MMAP:
 298                     for (i = 0; i < n_buffers; ++i)
 299                             if (-1 == munmap(buffers[i].start, buffers[i].length))
 300                                     errno_exit("munmap");
 301                     break;
 302
 303             case IO_METHOD_USERPTR:
 304                     for (i = 0; i < n_buffers; ++i)
 305                             free(buffers[i].start);
 306                     break;
 307             }
 308
 309             free(buffers);
 310     }
 311
 312     static void init_read(unsigned int buffer_size)
 313     {
 314             buffers = calloc(1, sizeof(*buffers));
 315
 316             if (!buffers) {
 317                     fprintf(stderr, "Out of memory\\n");
 318                     exit(EXIT_FAILURE);
 319             }
 320
 321             buffers[0].length = buffer_size;
 322             buffers[0].start = malloc(buffer_size);
 323
 324             if (!buffers[0].start) {
 325                     fprintf(stderr, "Out of memory\\n");
 326                     exit(EXIT_FAILURE);
 327             }
 328     }
 329
 330     static void init_mmap(void)
 331     {
 332             struct v4l2_requestbuffers req;
 333
 334             CLEAR(req);
 335
 336             req.count = 4;
 337             req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 338             req.memory = V4L2_MEMORY_MMAP;
 339
 340             if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
 341                     if (EINVAL == errno) {
 342                             fprintf(stderr, "%s does not support "
 343                                      "memory mappingn", dev_name);
 344                             exit(EXIT_FAILURE);
 345                     } else {
 346                             errno_exit("VIDIOC_REQBUFS");
 347                     }
 348             }
 349
 350             if (req.count < 2) {
 351                     fprintf(stderr, "Insufficient buffer memory on %s\\n",
 352                              dev_name);
 353                     exit(EXIT_FAILURE);
 354             }
 355
 356             buffers = calloc(req.count, sizeof(*buffers));
 357
 358             if (!buffers) {
 359                     fprintf(stderr, "Out of memory\\n");
 360                     exit(EXIT_FAILURE);
 361             }
 362
 363             for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
 364                     struct v4l2_buffer buf;
 365
 366                     CLEAR(buf);
 367
 368                     buf.type        = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 369                     buf.memory      = V4L2_MEMORY_MMAP;
 370                     buf.index       = n_buffers;
 371
 372                     if (-1 == xioctl(fd, VIDIOC_QUERYBUF, &buf))
 373                             errno_exit("VIDIOC_QUERYBUF");
 374
 375                     buffers[n_buffers].length = buf.length;
 376                     buffers[n_buffers].start =
 377                             mmap(NULL /* start anywhere */,
 378                                   buf.length,
 379                                   PROT_READ | PROT_WRITE /* required */,
 380                                   MAP_SHARED /* recommended */,
 381                                   fd, buf.m.offset);
 382
 383                     if (MAP_FAILED == buffers[n_buffers].start)
 384                             errno_exit("mmap");
 385             }
 386     }
 387
 388     static void init_userp(unsigned int buffer_size)
 389     {
 390             struct v4l2_requestbuffers req;
 391
 392             CLEAR(req);
 393
 394             req.count  = 4;
 395             req.type   = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 396             req.memory = V4L2_MEMORY_USERPTR;
 397
 398             if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
 399                     if (EINVAL == errno) {
 400                             fprintf(stderr, "%s does not support "
 401                                      "user pointer i/on", dev_name);
 402                             exit(EXIT_FAILURE);
 403                     } else {
 404                             errno_exit("VIDIOC_REQBUFS");
 405                     }
 406             }
 407
 408             buffers = calloc(4, sizeof(*buffers));
 409
 410             if (!buffers) {
 411                     fprintf(stderr, "Out of memory\\n");
 412                     exit(EXIT_FAILURE);
 413             }
 414
 415             for (n_buffers = 0; n_buffers < 4; ++n_buffers) {
 416                     buffers[n_buffers].length = buffer_size;
 417                     buffers[n_buffers].start = malloc(buffer_size);
 418
 419                     if (!buffers[n_buffers].start) {
 420                             fprintf(stderr, "Out of memory\\n");
 421                             exit(EXIT_FAILURE);
 422                     }
 423             }
 424     }
 425
 426     static void init_device(void)
 427     {
 428             struct v4l2_capability cap;
 429             struct v4l2_cropcap cropcap;
 430             struct v4l2_crop crop;
 431             struct v4l2_format fmt;
 432             unsigned int min;
 433
 434             if (-1 == xioctl(fd, VIDIOC_QUERYCAP, &cap)) {
 435                     if (EINVAL == errno) {
 436                             fprintf(stderr, "%s is no V4L2 device\\n",
 437                                      dev_name);
 438                             exit(EXIT_FAILURE);
 439                     } else {
 440                             errno_exit("VIDIOC_QUERYCAP");
 441                     }
 442             }
 443
 444             if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
 445                     fprintf(stderr, "%s is no video capture device\\n",
 446                              dev_name);
 447                     exit(EXIT_FAILURE);
 448             }
 449
 450             switch (io) {
 451             case IO_METHOD_READ:
 452                     if (!(cap.capabilities & V4L2_CAP_READWRITE)) {
 453                             fprintf(stderr, "%s does not support read i/o\\n",
 454                                      dev_name);
 455                             exit(EXIT_FAILURE);
 456                     }
 457                     break;
 458
 459             case IO_METHOD_MMAP:
 460             case IO_METHOD_USERPTR:
 461                     if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
 462                             fprintf(stderr, "%s does not support streaming i/o\\n",
 463                                      dev_name);
 464                             exit(EXIT_FAILURE);
 465                     }
 466                     break;
 467             }
 468
 469
 470             /* Select video input, video standard and tune here. */
 471
 472
 473             CLEAR(cropcap);
 474
 475             cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 476
 477             if (0 == xioctl(fd, VIDIOC_CROPCAP, &cropcap)) {
 478                     crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 479                     crop.c = cropcap.defrect; /* reset to default */
 480
 481                     if (-1 == xioctl(fd, VIDIOC_S_CROP, &crop)) {
 482                             switch (errno) {
 483                             case EINVAL:
 484                                     /* Cropping not supported. */
 485                                     break;
 486                             default:
 487                                     /* Errors ignored. */
 488                                     break;
 489                             }
 490                     }
 491             } else {
 492                     /* Errors ignored. */
 493             }
 494
 495
 496             CLEAR(fmt);
 497
 498             fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 499             if (force_format) {
 500                     fmt.fmt.pix.width       = 640;
 501                     fmt.fmt.pix.height      = 480;
 502                     fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
 503                     fmt.fmt.pix.field       = V4L2_FIELD_INTERLACED;
 504
 505                     if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
 506                             errno_exit("VIDIOC_S_FMT");
 507
 508                     /* Note VIDIOC_S_FMT may change width and height. */
 509             } else {
 510                     /* Preserve original settings as set by v4l2-ctl for example */
 511                     if (-1 == xioctl(fd, VIDIOC_G_FMT, &fmt))
 512                             errno_exit("VIDIOC_G_FMT");
 513             }
 514
 515             /* Buggy driver paranoia. */
 516             min = fmt.fmt.pix.width * 2;
 517             if (fmt.fmt.pix.bytesperline < min)
 518                     fmt.fmt.pix.bytesperline = min;
 519             min = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;
 520             if (fmt.fmt.pix.sizeimage < min)
 521                     fmt.fmt.pix.sizeimage = min;
 522
 523             switch (io) {
 524             case IO_METHOD_READ:
 525                     init_read(fmt.fmt.pix.sizeimage);
 526                     break;
 527
 528             case IO_METHOD_MMAP:
 529                     init_mmap();
 530                     break;
 531
 532             case IO_METHOD_USERPTR:
 533                     init_userp(fmt.fmt.pix.sizeimage);
 534                     break;
 535             }
 536     }
 537
 538     static void close_device(void)
 539     {
 540             if (-1 == close(fd))
 541                     errno_exit("close");
 542
 543             fd = -1;
 544     }
 545
 546     static void open_device(void)
 547     {
 548             struct stat st;
 549
 550             if (-1 == stat(dev_name, &st)) {
 551                     fprintf(stderr, "Cannot identify '%s': %d, %s\\n",
 552                              dev_name, errno, strerror(errno));
 553                     exit(EXIT_FAILURE);
 554             }
 555
 556             if (!S_ISCHR(st.st_mode)) {
 557                     fprintf(stderr, "%s is no devicen", dev_name);
 558                     exit(EXIT_FAILURE);
 559             }
 560
 561             fd = open(dev_name, O_RDWR /* required */ | O_NONBLOCK, 0);
 562
 563             if (-1 == fd) {
 564                     fprintf(stderr, "Cannot open '%s': %d, %s\\n",
 565                              dev_name, errno, strerror(errno));
 566                     exit(EXIT_FAILURE);
 567             }
 568     }
 569
 570     static void usage(FILE *fp, int argc, char **argv)
 571     {
 572             fprintf(fp,
 573                      "Usage: %s [options]\\n\\n"
 574                      "Version 1.3\\n"
 575                      "Options:\\n"
 576                      "-d | --device name   Video device name [%s]n"
 577                      "-h | --help          Print this messagen"
 578                      "-m | --mmap          Use memory mapped buffers [default]n"
 579                      "-r | --read          Use read() callsn"
 580                      "-u | --userp         Use application allocated buffersn"
 581                      "-o | --output        Outputs stream to stdoutn"
 582                      "-f | --format        Force format to 640x480 YUYVn"
 583                      "-c | --count         Number of frames to grab [%i]n"
 584                      "",
 585                      argv[0], dev_name, frame_count);
 586     }
 587
 588     static const char short_options[] = "d:hmruofc:";
 589
 590     static const struct option
 591     long_options[] = {
 592             { "device", required_argument, NULL, 'd' },
 593             { "help",   no_argument,       NULL, 'h' },
 594             { "mmap",   no_argument,       NULL, 'm' },
 595             { "read",   no_argument,       NULL, 'r' },
 596             { "userp",  no_argument,       NULL, 'u' },
 597             { "output", no_argument,       NULL, 'o' },
 598             { "format", no_argument,       NULL, 'f' },
 599             { "count",  required_argument, NULL, 'c' },
 600             { 0, 0, 0, 0 }
 601     };
 602
 603     int main(int argc, char **argv)
 604     {
 605             dev_name = "/dev/video0";
 606
 607             for (;;) {
 608                     int idx;
 609                     int c;
 610
 611                     c = getopt_long(argc, argv,
 612                                     short_options, long_options, &idx);
 613
 614                     if (-1 == c)
 615                             break;
 616
 617                     switch (c) {
 618                     case 0: /* getopt_long() flag */
 619                             break;
 620
 621                     case 'd':
 622                             dev_name = optarg;
 623                             break;
 624
 625                     case 'h':
 626                             usage(stdout, argc, argv);
 627                             exit(EXIT_SUCCESS);
 628
 629                     case 'm':
 630                             io = IO_METHOD_MMAP;
 631                             break;
 632
 633                     case 'r':
 634                             io = IO_METHOD_READ;
 635                             break;
 636
 637                     case 'u':
 638                             io = IO_METHOD_USERPTR;
 639                             break;
 640
 641                     case 'o':
 642                             out_buf++;
 643                             break;
 644
 645                     case 'f':
 646                             force_format++;
 647                             break;
 648
 649                     case 'c':
 650                             errno = 0;
 651                             frame_count = strtol(optarg, NULL, 0);
 652                             if (errno)
 653                                     errno_exit(optarg);
 654                             break;
 655
 656                     default:
 657                             usage(stderr, argc, argv);
 658                             exit(EXIT_FAILURE);
 659                     }
 660             }
 661
 662             open_device();
 663             init_device();
 664             start_capturing();
 665             mainloop();
 666             stop_capturing();
 667             uninit_device();
 668             close_device();
 669             fprintf(stderr, "\\n");
 670             return 0;
 671     }