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

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