USB摄像头linux实现方法是什么

本篇内容介绍了"USB摄像头linux实现方法是什么"的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！

一、前言

做嵌入式linux上的开发很多年了，扳手指头算算，也起码9年了，陆陆续续做过很过诸如需要读取外接的USB摄像头或者CMOS摄像机的程序，实时采集视频，将图像传到前端，或者对图像进行人脸分析处理，最开始尝试的就是QCamera来处理，直接歇菜放弃，后面通过搜索发现都说要用v4l2视频框架来进行，于是东搞搞西搞搞尝试了很多次，终于整出来了，前后完善了好几年，无论写什么程序，发现要简简单单的实现基础的功能，都是非常快速而且容易的，但是想要做得好做得精，要花不少的精力时间去完善，适应各种不同的场景，比如就说用v4l2加载摄像头这个，需要指定设备文件来读取，而现场不可能让用户来给你指定，频繁的拔插也会导致设备文件名的改动，所以必须找到一个机制自动寻找你想要的摄像机的设备文件名称，比如开个定时器去调用linux命令来处理，甚至在不同的系统平台上要执行的命令还有些许的区别，如果本地有多个摄像头还需要区分左右之类的时候，那就只能通过断电先后上电顺序次序来区分了。

linux方案处理流程：

1. 调用封装的函数findCamera实时查找摄像头设备文件名。

2. 调用::open函数打开设备文件。

3. 调用封装的函数initCamera初始化摄像头参数（图片格式、分辨率等）。

4. 调用::select函数从缓冲区取出一个缓冲帧。

5. 缓冲帧数据是yuyv格式的，需要转换rgb24再转成QImage。

6. 拿到图片进行绘制、人脸分析等。

7. 关闭设备文件。

二、功能特点

1. 同时支持windows、linux、嵌入式linux上的USB摄像头实时采集。

2. 支持多路USB摄像头多线程实时采集。

3. 在嵌入式linux设备上，自动查找USB设备文件并加载。

4. 可手动设置设备文件名称，手动设置后按照手动设置的设备文件加载。

5. 在嵌入式linux设备上支持人脸识别接口，实时绘制人脸框。

6. 具有打开、暂停、继续、关闭、截图等常规功能。

7. 可设置两路OSD标签，分别设置文本、颜色、字号、位置等。

8. 可作为视频监控系统使用。

三、效果图

四、核心代码

void CameraLinux::run(){    while (!stopped) {        if (!cameraOk) {            msleep(10);            continue;        }        if (isPause) {            //这里需要假设正常,暂停期间继续更新时间            lastTime = QDateTime::currentDateTime();            msleep(10);            continue;        }        QImage image = readImage();        if (!image.isNull()) {            if (isSnap) {                emit snapImage(image);                isSnap = false;            }            if (findFaceOne) {                findFace(image);            }            if (findFaceRect) {                image = drawFace(image);            }            lastTime = QDateTime::currentDateTime();            emit receiveImage(image);        }        msleep(interval);    }    this->closeCamera();    this->initData();}QDateTime CameraLinux::getLastTime() const{    return this->lastTime;}QString CameraLinux::getCameraName() const{    return this->cameraName;}int CameraLinux::getCameraWidth() const{    return this->cameraWidth;}int CameraLinux::getCameraHeight() const{    return this->cameraHeight;}void CameraLinux::sleep(int msec){    if (msec > 0) {        QTime endTime = QTime::currentTime().addMSecs(msec);        while (QTime::currentTime() < endTime) {            QCoreApplication::processEvents(QEventLoop::AllEvents, 100);        }    }}void CameraLinux::initData(){    stopped = false;    isPause = false;    isSnap = false;    cameraOk = false;    cameraHwnd = -1;    errorCount = 0;}void CameraLinux::readData(){    QStringList cameraNames;    while (!process->atEnd()) {        //逐行读取返回的结果 过滤video开头的是摄像头设备文件        QString line = process->readLine();        if (line.startsWith("video")) {            line = line.replace("\n", "");            cameraNames << QString("/dev/%1").arg(line);        }    }    if (cameraNames.count() > 0) {        cameraName = cameraNames.first();        emit receiveCamera(cameraNames);        qDebug() << TIMEMS << cameraNames;    }}bool CameraLinux::initCamera(){    //如果没有指定设备文件名称(默认auto)则查找    if (cameraName == "auto") {        findCamera();    }    //延时判断是否获取到了设备文件    sleep(300);    return openCamera();}void CameraLinux::findCamera(){    if (process->state() == QProcess::NotRunning) {        process->start("ls /dev/");    }}bool CameraLinux::openCamera(){#ifdef Q_OS_LINUX    if (cameraName.length() > 5) {        cameraHwnd = ::open(cameraName.toUtf8().data(), O_RDWR | O_NONBLOCK, 0);    }    if (cameraHwnd < 0) {        qDebug() << TIMEMS << "open camera error";        return false;    }    //查询设备属性    struct v4l2_capability capability;    if (::ioctl(cameraHwnd, VIDIOC_QUERYCAP, &capability) < 0) {        qDebug() << TIMEMS << "error in VIDIOC_QUERYCAP";        ::close(cameraHwnd);        return false;    }    if (!(capability.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {        qDebug() << TIMEMS << "it is not a video capture device";        ::close(cameraHwnd);        return false;    }    if (!(capability.capabilities & V4L2_CAP_STREAMING)) {        qDebug() << TIMEMS << "it can not streaming";        ::close(cameraHwnd);        return false;    }    if (capability.capabilities == 0x4000001) {        qDebug() << TIMEMS << "capabilities" << "V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_STREAMING";    }    //设置视频输入源    int input = 0;    if (::ioctl(cameraHwnd, VIDIOC_S_INPUT, &input) < 0) {        qDebug() << TIMEMS << "error in VIDIOC_S_INPUT";        ::close(cameraHwnd);        return false;    }    //设置图片格式和分辨率    struct v4l2_format format;    format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;    //多种格式 V4L2_PIX_FMT_YUV420  V4L2_PIX_FMT_YUYV(422) V4L2_PIX_FMT_RGB565    format.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;    //部分硬件花屏要设置成 V4L2_FIELD_NONE    format.fmt.pix.field = V4L2_FIELD_INTERLACED;    format.fmt.pix.width = cameraWidth;    format.fmt.pix.height = cameraHeight;    int bpp = 16;    //format.fmt.pix.bytesperline = width * bpp / 8;    //format.fmt.pix.sizeimage = cameraWidth * cameraHeight * bpp / 8;    if (::ioctl(cameraHwnd, VIDIOC_S_FMT, &format) < 0) {        ::close(cameraHwnd);        return false;    }    //查看图片格式和分辨率,判断是否设置成功    if (::ioctl(cameraHwnd, VIDIOC_G_FMT, &format) < 0) {        qDebug() << TIMEMS << "error in VIDIOC_G_FMT";        ::close(cameraHwnd);        return false;    }    //重新打印下宽高看下是否真正设置成功    struct v4l2_pix_format pix = format.fmt.pix;    quint32 pixelformat = pix.pixelformat;    qDebug() << TIMEMS << "cameraWidth" << cameraWidth << "cameraHeight" << cameraHeight << "width" << pix.width << "height" << pix.height;    qDebug() << TIMEMS << "pixelformat" << QString("%1%2%3%4").arg(QChar(pixelformat & 0xFF)).arg(QChar((pixelformat >> 8) & 0xFF)).arg(QChar((pixelformat >> 16) & 0xFF)).arg(QChar((pixelformat >> 24) & 0xFF));    //重新设置宽高为真实的宽高    cameraWidth = pix.width;    cameraHeight = pix.height;    //设置帧格式    struct v4l2_streamparm streamparm;    streamparm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;    streamparm.parm.capture.timeperframe.numerator = 1;    streamparm.parm.capture.timeperframe.denominator = 25;    streamparm.parm.capture.capturemode = 0;    if (::ioctl(cameraHwnd, VIDIOC_S_PARM, &streamparm) < 0) {        qDebug() << TIMEMS << "error in VIDIOC_S_PARM";        ::close(cameraHwnd);        return false;    }    if (::ioctl(cameraHwnd, VIDIOC_G_PARM, &streamparm) < 0) {        qDebug() << TIMEMS << "error in VIDIOC_G_PARM";        ::close(cameraHwnd);        return false;    }    //申请和管理缓冲区    struct v4l2_requestbuffers requestbuffers;    requestbuffers.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;    requestbuffers.memory = V4L2_MEMORY_MMAP;    requestbuffers.count = 1;    if (::ioctl(cameraHwnd, VIDIOC_REQBUFS, &requestbuffers) < 0) {        qDebug() << TIMEMS << "error in VIDIOC_REQBUFS";        ::close(cameraHwnd);        return false;    }    buff_yuv422 = (uchar *)malloc(cameraWidth * cameraHeight * bpp / 8);    buff_yuv420 = (uchar *)malloc(cameraWidth * cameraHeight * bpp / 8);    buff_rgb24 = (uchar *)malloc(cameraWidth * cameraHeight * 24 / 8);    buff_img = (ImgBuffer *)calloc(1, sizeof(ImgBuffer));    if (buff_img == NULL) {        qDebug() << TIMEMS << "error in calloc";        ::close(cameraHwnd);        return false;    }    struct v4l2_buffer buffer;    for (int index = 0; index < 1; index++) {        buffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;        buffer.memory = V4L2_MEMORY_MMAP;        buffer.index = index;        if (::ioctl(cameraHwnd, VIDIOC_QUERYBUF, &buffer) < 0) {            qDebug() << TIMEMS << "error in VIDIOC_QUERYBUF";            ::free(buff_img);            ::close(cameraHwnd);            return false;        }        buff_img[index].length = buffer.length;        buff_img[index].start = (quint8 *)mmap(NULL, buffer.length, PROT_READ | PROT_WRITE, MAP_SHARED, cameraHwnd, buffer.m.offset);        if (MAP_FAILED == buff_img[index].start) {            qDebug() << TIMEMS << "error in mmap";            ::free(buff_img);            ::close(cameraHwnd);            return false;        }        //把缓冲帧放入队列        if (::ioctl(cameraHwnd, VIDIOC_QBUF, &buffer) < 0) {            qDebug() << TIMEMS << "error in VIDIOC_QBUF";            for (int i = 0; i <= index; i++) {                munmap(buff_img[i].start, buff_img[i].length);            }            ::free(buff_img);            ::close(cameraHwnd);            return false;        }    }    enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;    if (::ioctl(cameraHwnd, VIDIOC_STREAMON, &type) < 0) {        qDebug() << TIMEMS << "error in VIDIOC_STREAMON";        for (int i = 0; i < 1; i++) {            munmap(buff_img[i].start, buff_img[i].length);        }        ::free(buff_img);        ::close(cameraHwnd);        return false;    }    cameraOk = true;#endif    qDebug() << TIMEMS << "open camera ok";    return cameraOk;}void CameraLinux::closeCamera(){#ifdef Q_OS_LINUX    if (cameraOk && buff_img != NULL) {        //停止摄像头采集        enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;        if (::ioctl(cameraHwnd, VIDIOC_STREAMOFF, &type) < 0) {            qDebug() << TIMEMS << "error in VIDIOC_STREAMOFF";        }        //解除内存映射        for (int i = 0; i < 1; i++) {            munmap((buff_img)[i].start, (buff_img)[i].length);        }        //关闭设备文件        ::close(cameraHwnd);        qDebug() << TIMEMS << "close camera ok";    }    //释放资源    ::free(buff_img);    buff_img = NULL;    ::free(buff_yuv422);    buff_yuv422 = NULL;    ::free(buff_yuv420);    buff_yuv420 = NULL;    ::free(buff_rgb24);    buff_rgb24 = NULL;    cameraOk = false;    cameraHwnd = -1;#endif}int CameraLinux::readFrame(){    int index = -1;#ifdef Q_OS_LINUX    //等待摄像头采集到一桢数据    for (;;) {        fd_set fds;        struct timeval tv;        FD_ZERO(&fds);        FD_SET(cameraHwnd, &fds);        tv.tv_sec = 2;        tv.tv_usec = 0;        int r = ::select(cameraHwnd + 1, &fds, NULL, NULL, &tv);        if (-1 == r) {            if (EINTR == errno) {                continue;            }            return -1;        } else if (0 == r) {            return -1;        } else {            //采集到一张图片 跳出循环            break;        }    }    //从缓冲区取出一个缓冲帧    struct v4l2_buffer buffer;    buffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;    buffer.memory = V4L2_MEMORY_MMAP;    if (::ioctl(cameraHwnd, VIDIOC_DQBUF, &buffer) < 0) {        qDebug() << TIMEMS << "error in VIDIOC_DQBUF";        return -1;    }    memcpy(buff_yuv422, (uchar *)buff_img[buffer.index].start, buff_img[buffer.index].length);    //将取出的缓冲帧放回缓冲区    if (::ioctl(cameraHwnd, VIDIOC_QBUF, &buffer) < 0) {        qDebug() << TIMEMS << "error in VIDIOC_QBUF";        return -1;    }    index = buffer.index;#endif    return index;}

"USB摄像头linux实现方法是什么"的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注网站，小编将为大家输出更多高质量的实用文章！