技触IPC Camera试玩儿

新入手一部技触USB IPC Camera摄像头，简要规格如下：

1.USB Plug and PLay

2.HD Resolution(最大支持1080P）

3.Wide Screen Video

4.Built-in Microphone

应用平台：

支持平台抖音，快手，微信，QQ，腾讯会议，钉钉，ZOOM会议，PotPlayer AMCAP, ECAPVideo Cap, SKYPE等等。

操作系统：

免驱动，即插即用，支持win xp/win7,win10, android,Linux.

输出图像格式：

MJPEG/YUV.

供电电压:

USB DC5V.

产品信息就这些，下面介绍一些玩儿法。

---

1.安装摄像头

直接将摄像头USB接口插入电脑USB母口，dmesg输出如下：

设备文件系统出现了两个设备video设备节点，至于为什么是两个而不是一个，先行按下，后面分析代码的时候在找原因。

测试１：使用python + opencv 测试

安装python-opencv库.

sudo apt-get install python-opencv

测试代码：

import numpy as np
import cv2 as cv
cap = cv.VideoCapture(0)
pic = 0
while(True):
    ret, frame = cap.read()
    gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
    cv.imshow('frame',gray)
    w = cap.get(cv.CAP_PROP_FRAME_WIDTH)
    h = cap.get(cv.CAP_PROP_FRAME_HEIGHT)
    pic=pic+1
    print w, h, pic
    if cv.waitKey(1) & 0xFF == ord('q'):
    break
 
cap.release()
cv.destroyAllWindows()

测试结果：

测试2：手搓V4L2代码实现：

#include <string.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h> 
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <linux/videodev2.h>
 
#define CLEAR(x) memset(&(x), 0, sizeof(x))
 
enum io_method {
  IO_METHOD_READ,
  IO_METHOD_MMAP,
  IO_METHOD_USERPTR,
};
 
struct buffer {
  void *start;
  size_t length;
};
 
char* dev_name;
enum io_method io = IO_METHOD_MMAP;
int fd = -1;
struct buffer* buffers;
unsigned int n_buffers;
int out_buf;
int force_format = 1;
int frame_count = 100;
int width = 640;
int height = 480;
FILE* f;
 
void errno_exit(const char *s)
{
  fprintf(stderr, "%s error %d, %s\n", s, errno, strerror(errno));
  exit(-1);
}
 
int xioctl(int fh, int request, void *arg)
{
  int r;
 
  do {
    r = ioctl(fh, request, arg);
  } while (-1 == r && EINTR == errno);
 
  return r;
}
 
void process_image(const void *p, int size)
{
  /*if (out_buf)
    fwrite(p, size, 1, stdout);
  fflush(stderr);
  fprintf(stderr, ".");
  fflush(stdout);*/
  fwrite(p, size, 1, f);
}
 
int read_frame(void)
{
  struct v4l2_buffer buf;
  unsigned int i;
 
  switch (io) {
  case IO_METHOD_READ:
    if (-1 == read(fd, buffers[0].start, buffers[0].length)) {
      switch (errno) {
      case EAGAIN:
        return 0;
 
      case EIO:
        // Could ignore EIO, see spec. fall through
 
      default:
        errno_exit("read");
      }
    }
 
    process_image(buffers[0].start, buffers[0].length);
    break;
 
  case IO_METHOD_MMAP:
    CLEAR(buf);
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;
    if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
      switch (errno) {
      case EAGAIN:
        return 0;
 
      case EIO:
        // Could ignore EIO, see spec. fall through
 
      default:
        errno_exit("VIDIOC_DQBUF");
      }
    }
 
    assert(buf.index < n_buffers);
    process_image(buffers[buf.index].start, buf.bytesused);
    if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
      errno_exit("VIDIOC_QBUF");
    break;
 
  case IO_METHOD_USERPTR:
    CLEAR(buf);
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_USERPTR;
 
    if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
      switch (errno) {
      case EAGAIN:
        return 0;
 
      case EIO:
        // Could ignore EIO, see spec. fall through
 
      default:
        errno_exit("VIDIOC_DQBUF");
      }
    }
 
    for (i = 0; i < n_buffers; ++i)
    if (buf.m.userptr == (unsigned long)buffers[i].start && buf.length == buffers[i].length)
      break;
 
    assert(i < n_buffers);
    process_image((void *)buf.m.userptr, buf.bytesused);
    if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
      errno_exit("VIDIOC_QBUF");
    break;
  }
 
  return 1;
}
 
void mainloop(void)
{
  unsigned int count = frame_count;
  while (count-- > 0) {
    for (;;) {
      fd_set fds;
      struct timeval tv;
      int r;
 
      FD_ZERO(&fds);
      FD_SET(fd, &fds);
 
      // Timeout
      tv.tv_sec = 5;
      tv.tv_usec = 0;
 
      r = select(fd + 1, &fds, NULL, NULL, &tv);
      if (-1 == r) {
        if (EINTR == errno)
          continue;
        errno_exit("select");
      }
 
      if (0 == r) {
        fprintf(stderr, "select timeout\n");
        exit(EXIT_FAILURE);
      }
 
      if (read_frame())
        break;
      // EAGAIN - continue select loop
    }
  }
}
 
void stop_capturing(void)
{
  enum v4l2_buf_type type;
 
  switch (io) {
  case IO_METHOD_READ:
    // Nothing to do
    break;
 
  case IO_METHOD_MMAP:
  case IO_METHOD_USERPTR:
    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if (-1 == xioctl(fd, VIDIOC_STREAMOFF, &type))
      errno_exit("VIDIOC_STREAMOFF");
    break;
  }
}
 
void start_capturing(void)
{
  unsigned int i;
  enum v4l2_buf_type type;
 
  switch (io) {
  case IO_METHOD_READ:
    // Nothing to do
    break;
 
  case IO_METHOD_MMAP:
    for (i = 0; i < n_buffers; ++i) {
      struct v4l2_buffer buf;
      CLEAR(buf);
      buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
      buf.memory = V4L2_MEMORY_MMAP;
      buf.index = i;
 
      if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
        errno_exit("VIDIOC_QBUF");
    }
    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if (-1 == xioctl(fd, VIDIOC_STREAMON, &type))
      errno_exit("VIDIOC_STREAMON");
    break;
 
  case IO_METHOD_USERPTR:
    for (i = 0; i < n_buffers; ++i) {
      struct v4l2_buffer buf;
      CLEAR(buf);
      buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
      buf.memory = V4L2_MEMORY_USERPTR;
      buf.index = i;
      buf.m.userptr = (unsigned long)buffers[i].start;
      buf.length = buffers[i].length;
 
      if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
        errno_exit("VIDIOC_QBUF");
    }
    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if (-1 == xioctl(fd, VIDIOC_STREAMON, &type))
      errno_exit("VIDIOC_STREAMON");
    break;
  }
 
  f = fopen("usb.yuv", "w");
  if (!f) {
    errno_exit("fail to open file");
  }
}
 
void uninit_device(void)
{
  unsigned int i;
 
  switch (io) {
  case IO_METHOD_READ:
    free(buffers[0].start);
    break;
 
  case IO_METHOD_MMAP:
    for (i = 0; i < n_buffers; ++i)
    if (-1 == munmap(buffers[i].start, buffers[i].length))
      errno_exit("munmap");
    break;
 
  case IO_METHOD_USERPTR:
    for (i = 0; i < n_buffers; ++i)
      free(buffers[i].start);
    break;
  }
 
  free(buffers);
  fclose(f);
}
 
void init_read(unsigned int buffer_size)
{
  buffers = (struct buffer*)calloc(1, sizeof(*buffers));
  if (!buffers) {
    fprintf(stderr, "Out of memory\n");
    exit(EXIT_FAILURE);
  }
 
  buffers[0].length = buffer_size;
  buffers[0].start = malloc(buffer_size);
 
  if (!buffers[0].start) {
    fprintf(stderr, "Out of memory\n");
    exit(EXIT_FAILURE);
  }
}
 
void init_mmap(void)
{
  struct v4l2_requestbuffers req;
  CLEAR(req);
  req.count = 4;
  req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  req.memory = V4L2_MEMORY_MMAP;
  if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
    if (EINVAL == errno) {
      fprintf(stderr, "%s does not support memory mappingn\n", dev_name);
      exit(EXIT_FAILURE);
    } else {
      errno_exit("VIDIOC_REQBUFS");
    }
  }
 
  if (req.count < 2) {
    fprintf(stderr, "Insufficient buffer memory on %s\n", dev_name);
    exit(EXIT_FAILURE);
  }
 
  buffers = (struct buffer*)calloc(req.count, sizeof(*buffers));
  if (!buffers) {
    fprintf(stderr, "Out of memory\n");
    exit(EXIT_FAILURE);
  }
 
  for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
    struct v4l2_buffer buf;
    CLEAR(buf);
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;
    buf.index = n_buffers;
    if (-1 == xioctl(fd, VIDIOC_QUERYBUF, &buf))
      errno_exit("VIDIOC_QUERYBUF");
 
    buffers[n_buffers].length = buf.length;
    buffers[n_buffers].start =
      mmap(NULL, // start anywhere
      buf.length,
      PROT_READ | PROT_WRITE, // required
      MAP_SHARED, // recommended
      fd, buf.m.offset);
 
    if (MAP_FAILED == buffers[n_buffers].start)
      errno_exit("mmap");
  }
}
 
void init_userp(unsigned int buffer_size)
{
  struct v4l2_requestbuffers req;
  CLEAR(req);
 
  req.count = 4;
  req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  req.memory = V4L2_MEMORY_USERPTR;
 
  if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
    if (EINVAL == errno) {
      fprintf(stderr, "%s does not support user pointer i/on", dev_name);
      exit(EXIT_FAILURE);
    } else {
      errno_exit("VIDIOC_REQBUFS");
    }
  }
 
  buffers = (struct buffer*)calloc(4, sizeof(*buffers));
  if (!buffers) {
    fprintf(stderr, "Out of memory\n");
    exit(EXIT_FAILURE);
  }
 
  for (n_buffers = 0; n_buffers < 4; ++n_buffers) {
    buffers[n_buffers].length = buffer_size;
    buffers[n_buffers].start = malloc(buffer_size);
 
    if (!buffers[n_buffers].start) {
      fprintf(stderr, "Out of memory\n");
      exit(EXIT_FAILURE);
    }
  }
}
 
void init_device(void)
{
  struct v4l2_capability cap;
  struct v4l2_cropcap cropcap;
  struct v4l2_crop crop;
  struct v4l2_format fmt;
  unsigned int min;
 
  if (-1 == xioctl(fd, VIDIOC_QUERYCAP, &cap)) {
    if (EINVAL == errno) {
      fprintf(stderr, "%s is no V4L2 device\n", dev_name);
      exit(EXIT_FAILURE);
    } else {
      errno_exit("VIDIOC_QUERYCAP");
    }
  }
 
  if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
    fprintf(stderr, "%s is no video capture device\n", dev_name);
    exit(EXIT_FAILURE);
  }
 
  switch (io) {
  case IO_METHOD_READ:
    if (!(cap.capabilities & V4L2_CAP_READWRITE)) {
      fprintf(stderr, "%s does not support read i/o\n", dev_name);
      exit(EXIT_FAILURE);
    }
    break;
 
  case IO_METHOD_MMAP:
  case IO_METHOD_USERPTR:
    if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
      fprintf(stderr, "%s does not support streaming i/o\n", dev_name);
      exit(EXIT_FAILURE);
    }
    break;
  }
 
  // Select video input, video standard and tune here
  CLEAR(cropcap);
  cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  if (0 == xioctl(fd, VIDIOC_CROPCAP, &cropcap)) {
    crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    crop.c = cropcap.defrect; // reset to default
    if (-1 == xioctl(fd, VIDIOC_S_CROP, &crop)) {
      switch (errno) {
      case EINVAL:
        // Cropping not supported
        break;
      default:
        // Errors ignored
        break;
      }
    }
  } else {
    // Errors ignored
  }
 
  CLEAR(fmt);
  fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  if (force_format) {
    fmt.fmt.pix.width = width;
    fmt.fmt.pix.height = height;
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
    fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
 
    // Note VIDIOC_S_FMT may change width and height
    if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
      errno_exit("VIDIOC_S_FMT");
  } else {
    // Preserve original settings as set by v4l2-ctl for example
    if (-1 == xioctl(fd, VIDIOC_G_FMT, &fmt))
      errno_exit("VIDIOC_G_FMT");
  }
 
  // Buggy driver paranoia
  min = fmt.fmt.pix.width * 2;
  if (fmt.fmt.pix.bytesperline < min)
    fmt.fmt.pix.bytesperline = min;
  min = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;
  if (fmt.fmt.pix.sizeimage < min)
    fmt.fmt.pix.sizeimage = min;
 
  switch (io) {
  case IO_METHOD_READ:
    init_read(fmt.fmt.pix.sizeimage);
    break;
 
  case IO_METHOD_MMAP:
    init_mmap();
    break;
 
  case IO_METHOD_USERPTR:
    init_userp(fmt.fmt.pix.sizeimage);
    break;
  }
}
 
void close_device(void)
{
  if (-1 == close(fd))
    errno_exit("close");
 
  fd = -1;
}
 
void open_device(void)
{
  struct stat st;
  if (-1 == stat(dev_name, &st)) {
    fprintf(stderr, "Cannot identify '%s': %d, %s\n", dev_name, errno, strerror(errno));
    exit(-1);
  }
 
  if (!S_ISCHR(st.st_mode)) {
    fprintf(stderr, "%s is no devicen\n", dev_name);
    exit(-1);
  }
 
  fd = open(dev_name, O_RDWR | O_NONBLOCK, 0); // O_RDWR: required
  if (-1 == fd) {
    fprintf(stderr, "Cannot open '%s': %d, %s\n", dev_name, errno, strerror(errno));
    exit(-1);
  }
}
 
int main(void)
{
  // reference: https://linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/capture.c.html
  dev_name = "/dev/video0";
 
  open_device();
  init_device();
  start_capturing();
  mainloop();
  stop_capturing();
  uninit_device();
  close_device();
 
  fprintf(stdout, "test finish\n");
  return 0;
}

将生成的usb.yuv用ffplay播放器播放：

ffplay -i usb.yuv -pixel_format yuyv422 -video_size 640*480

获取设备图像支持参数：

#include <string.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h> 
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <linux/videodev2.h>
 
#define CLEAR(x) memset(&(x), 0, sizeof(x))
char* dev_name;
int fd = -1;
int width = 640;
int height = 480;
FILE* f;
 
void errno_exit(const char *s)
{
    fprintf(stderr, "%s error %d, %s\n", s, errno, strerror(errno));
    exit(-1);
}
 
int xioctl(int fh, int request, void *arg)
{
    int r;
 
    do {
        r = ioctl(fh, request, arg);
    } while (-1 == r && EINTR == errno);
 
    return r;
}
 
 
void close_device(void)
{
    if (-1 == close(fd))
        errno_exit("close");
 
    fd = -1;
}
 
void open_device(void)
{
    struct stat st;
    if (-1 == stat(dev_name, &st)) {
        fprintf(stderr, "Cannot identify '%s': %d, %s\n", dev_name, errno, strerror(errno));
        exit(-1);
    }
 
    if (!S_ISCHR(st.st_mode)) {
        fprintf(stderr, "%s is no devicen\n", dev_name);
        exit(-1);
    }
 
    fd = open(dev_name, O_RDWR | O_NONBLOCK, 0); // O_RDWR: required
    if (-1 == fd) {
        fprintf(stderr, "Cannot open '%s': %d, %s\n", dev_name, errno, strerror(errno));
        exit(-1);
    }
}

void get_fmt(void)
{
    int ret;
    struct v4l2_fmtdesc fmt;

    memset(&fmt, 0, sizeof(fmt));
    fmt.index = 0;
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    while ((ret = ioctl(fd, VIDIOC_ENUM_FMT, &fmt)) == 0)
    {   
            fmt.index++;
            printf("{ pixelformat = ''%c%c%c%c'', description = ''%s'' }\n",
                     fmt.pixelformat & 0xFF, (fmt.pixelformat >> 8) & 0xFF, (fmt.pixelformat >> 16) & 0xFF,
                    (fmt.pixelformat >> 24) & 0xFF, fmt.description);
    }
}

void get_input(void)
{
    struct v4l2_input inp;
    inp.index = 0;
    while (ioctl (fd, VIDIOC_ENUMINPUT, &inp) == 0) {
        printf("%s : std: 0x%llx\n", , inp.std);
        inp.index++;
    }
}

void set_input(void)
{
    struct v4l2_input inp;
    inp.index = 0;
    if (ioctl (fd, VIDIOC_S_INPUT, &inp) < 0) {
        printf("set input error.\n");
    }
}


 
int main(void)
{
    // reference: https://linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/capture.c.html
    dev_name = "/dev/video0";
 
    open_device();
    get_fmt();
    get_input();
    set_input();
    close_device();

    return 0;
}

---

结束！