Linux上的C网络摄像头库？

是否有任何c库可以从Linux上的网络摄像头获取视频？

我们很多人都使用OpenCV(跨平台计算机视觉库,目前在v2.1上)

以下代码段从相机抓取帧,将它们转换为灰度并在屏幕上显示:

#include 
#include "cv.h"
#include "highgui.h"


typedef IplImage* (*callback_prototype)(IplImage*);


/* 
 * make_it_gray: custom callback to convert a colored frame to its grayscale version.
 * Remember that you must deallocate the returned IplImage* yourself after calling this function.
 */
IplImage* make_it_gray(IplImage* frame)
{
    // Allocate space for a new image
    IplImage* gray_frame = 0;
    gray_frame = cvCreateImage(cvSize(frame->width, frame->height), frame->depth, 1);
    if (!gray_frame)
    {
      fprintf(stderr, "!!! cvCreateImage failed!\n" );
      return NULL;
    }

    cvCvtColor(frame, gray_frame, CV_RGB2GRAY);
    return gray_frame; 
}

/*
 * process_video: retrieves frames from camera and executes a callback to do individual frame processing.
 * Keep in mind that if your callback takes too much time to execute, you might loose a few frames from 
 * the camera.
 */
void process_video(callback_prototype custom_cb)
{           
    // Initialize camera
    CvCapture *capture = 0;
    capture = cvCaptureFromCAM(-1);
    if (!capture) 
    {
      fprintf(stderr, "!!! Cannot open initialize webcam!\n" );
      return;
    }

    // Create a window for the video 
    cvNamedWindow("result", CV_WINDOW_AUTOSIZE);

    IplImage* frame = 0;
    char key = 0;
    while (key != 27) // ESC
    {    
      frame = cvQueryFrame(capture);
      if(!frame) 
      {
          fprintf( stderr, "!!! cvQueryFrame failed!\n" );
          break;
      }

      // Execute callback on each frame
      IplImage* processed_frame = (*custom_cb)(frame);

      // Display processed frame
      cvShowImage("result", processed_frame);

      // Release resources
      cvReleaseImage(&processed_frame);

      // Exit when user press ESC
      key = cvWaitKey(10);
    }

    // Free memory
    cvDestroyWindow("result");
    cvReleaseCapture(&capture);
}

int main( int argc, char **argv )
{
    process_video(make_it_gray);

    return 0;
}

v4l2 官方的例子

你得到什么:

./v4l2grab:捕获一些快照到文件 outNNN.ppm

./v4l2gl:使用OpenGL纹理(立即渲染,嘿!)和原始X11窗口(加上GLUT gluLookAt用于良好测量)在窗口上直播显示视频.

如何在Ubuntu 16.04上获取它:

sudo apt-get install libv4l-dev
sudo apt-get build-dep libv4l-dev
git clone git://linuxtv.org/v4l-utils.git
cd v4l-utils
# Matching the installed version of dpkg -s libv4l-dev
git checkout v4l-utils-1.10.0
./bootstrap.sh
./configure
make
# TODO: fails halfway, but it does not matter for us now.
cd contrib/tests
make

在Git树之外使用这些示例也很容易,只需将它们复制出来,使相对包含""绝对值<>,然后删除即可config.h.我已经为你完成了这个:https://github.com/cirosantilli/cpp-cheat/tree/09fe73d248f7da2e9c9f3eff2520a143c259f4a6/v4l2

来自docs的最小例子

该文档4.9.0包含的内容似乎是最低版本./v4l2grab的https://linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/v4l2grab-example.html.我需要对其进行最低限度的修补,然后我将补丁发送到http://www.spinics.net/lists/linux-media/(他们的文档在Linux内核树中作为第一个,整洁的)存在,在那里它被彻底忽略了.

用法:

gcc v4l2grab.c -lv4l2
./a.out

修补代码:

/* V4L2 video picture grabber
Copyright (C) 2009 Mauro Carvalho Chehab 

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 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#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;
}

标头仅面向对象的版本以供重用

从文档中的示例中提取,但其形式使其易于重用.

common_v4l2.h:

#ifndef COMMON_V4L2_H
#define COMMON_V4L2_H

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#include 
#include 

#define COMMON_V4L2_CLEAR(x) memset(&(x), 0, sizeof(x))

typedef struct {
    void *start;
    size_t length;
} CommonV4l2_Buffer;

typedef struct {
    int fd;
    CommonV4l2_Buffer *buffers;
    struct v4l2_buffer buf;
    unsigned int n_buffers;
} CommonV4l2;

void CommonV4l2_xioctl(int fh, unsigned long 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);
    }
}

void CommonV4l2_init(CommonV4l2 *this, char *dev_name, unsigned int x_res, unsigned int y_res) {
    enum v4l2_buf_type type;
    struct v4l2_format fmt;
    struct v4l2_requestbuffers req;
    unsigned int i;

    this->fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);
    if (this->fd < 0) {
        perror("Cannot open device");
        exit(EXIT_FAILURE);
    }
    COMMON_V4L2_CLEAR(fmt);
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    fmt.fmt.pix.width       = x_res;
    fmt.fmt.pix.height      = y_res;
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_RGB24;
    fmt.fmt.pix.field       = V4L2_FIELD_INTERLACED;
    CommonV4l2_xioctl(this->fd, VIDIOC_S_FMT, &fmt);
    if ((fmt.fmt.pix.width != x_res) || (fmt.fmt.pix.height != y_res))
        printf("Warning: driver is sending image at %dx%d\n",
            fmt.fmt.pix.width, fmt.fmt.pix.height);
    COMMON_V4L2_CLEAR(req);
    req.count = 2;
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP;
    CommonV4l2_xioctl(this->fd, VIDIOC_REQBUFS, &req);
    this->buffers = calloc(req.count, sizeof(*this->buffers));
    for (this->n_buffers = 0; this->n_buffers < req.count; ++this->n_buffers) {
        COMMON_V4L2_CLEAR(this->buf);
        this->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        this->buf.memory = V4L2_MEMORY_MMAP;
        this->buf.index = this->n_buffers;
        CommonV4l2_xioctl(this->fd, VIDIOC_QUERYBUF, &this->buf);
        this->buffers[this->n_buffers].length = this->buf.length;
        this->buffers[this->n_buffers].start = v4l2_mmap(NULL, this->buf.length,
            PROT_READ | PROT_WRITE, MAP_SHARED, this->fd, this->buf.m.offset);
        if (MAP_FAILED == this->buffers[this->n_buffers].start) {
            perror("mmap");
            exit(EXIT_FAILURE);
        }
    }
    for (i = 0; i < this->n_buffers; ++i) {
        COMMON_V4L2_CLEAR(this->buf);
        this->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        this->buf.memory = V4L2_MEMORY_MMAP;
        this->buf.index = i;
        CommonV4l2_xioctl(this->fd, VIDIOC_QBUF, &this->buf);
    }
    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    CommonV4l2_xioctl(this->fd, VIDIOC_STREAMON, &type);
}

void CommonV4l2_update_image(CommonV4l2 *this) {
    fd_set fds;
    int r;
    struct timeval tv;

    do {
        FD_ZERO(&fds);
        FD_SET(this->fd, &fds);

        /* Timeout. */
        tv.tv_sec = 2;
        tv.tv_usec = 0;

        r = select(this->fd + 1, &fds, NULL, NULL, &tv);
    } while ((r == -1 && (errno == EINTR)));
    if (r == -1) {
        perror("select");
        exit(EXIT_FAILURE);
    }
    COMMON_V4L2_CLEAR(this->buf);
    this->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    this->buf.memory = V4L2_MEMORY_MMAP;
    CommonV4l2_xioctl(this->fd, VIDIOC_DQBUF, &this->buf);
    CommonV4l2_xioctl(this->fd, VIDIOC_QBUF, &this->buf);
}

char * CommonV4l2_get_image(CommonV4l2 *this) {
    return ((char *)this->buffers[this->buf.index].start);
}

size_t CommonV4l2_get_image_size(CommonV4l2 *this) {
    return this->buffers[this->buf.index].length;
}

void CommonV4l2_deinit(CommonV4l2 *this) {
    unsigned int i;
    enum v4l2_buf_type type;

    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    CommonV4l2_xioctl(this->fd, VIDIOC_STREAMOFF, &type);
    for (i = 0; i < this->n_buffers; ++i)
        v4l2_munmap(this->buffers[i].start, this->buffers[i].length);
    v4l2_close(this->fd);
    free(this->buffers);
}

#endif

main.c:

#include 
#include 

#include "common_v4l2.h"

static void save_ppm(
    unsigned int i,
    unsigned int x_res,
    unsigned int y_res,
    size_t data_lenght,
    char *data
) {
    FILE *fout;
    char out_name[256];

    sprintf(out_name, "out%03d.ppm", i);
    fout = fopen(out_name, "w");
    if (!fout) {
        perror("error: fopen");
        exit(EXIT_FAILURE);
    }
    fprintf(fout, "P6\n%d %d 255\n", x_res, y_res);
    fwrite(data, data_lenght, 1, fout);
    fclose(fout);
}

int main(void) {
    CommonV4l2 common_v4l2;
    char *dev_name = "/dev/video0";
    struct buffer *buffers;
    unsigned int
        i,
        x_res = 640,
        y_res = 480
    ;

    CommonV4l2_init(&common_v4l2, dev_name, x_res, y_res);
    for (i = 0; i < 20; i++) {
        CommonV4l2_update_image(&common_v4l2);
        save_ppm(
            i,
            x_res,
            y_res,
            CommonV4l2_get_image_size(&common_v4l2),
            CommonV4l2_get_image(&common_v4l2)
        );
    }
    CommonV4l2_deinit(&common_v4l2);
    return EXIT_SUCCESS;
}

上游:https://github.com/cirosantilli/cpp-cheat/blob/be5d6444bddab93e95949b3388d92007b5ca916f/v4l2/common_v4l2.h

SDL

视频捕获在他们的路线图中:https://wiki.libsdl.org/Roadmap,我打赌它将在Linux上包装v4l.

当我们获得可移植性层时,它会比OpenCV更少膨胀.

你最好的选择可能是:video4linux(V4L)

它易于使用,功能强大.