Qt音视频开发38-USB摄像头解码linux方案

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：

调用封装的函数findCamera实时查找摄像头设备文件名。
调用::open函数打开设备文件。
调用封装的函数initCamera初始化摄像头参数（图片格式、分辨率等）。
调用::select函数从缓冲区取出一个缓冲帧。
缓冲帧数据是yuyv格式的，需要转换rgb24再转成QImage。
拿到图片进行绘制、人脸分析等。
关闭设备文件。

二、功能特点

同时支持windows、linux、嵌入式linux上的USB摄像头实时采集。
支持多路USB摄像头多线程实时采集。
在嵌入式linux设备上，自动查找USB设备文件并加载。
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。
在嵌入式linux设备上支持人脸识别接口，实时绘制人脸框。
具有打开、暂停、继续、关闭、截图等常规功能。
可设置两路OSD标签，分别设置文本、颜色、字号、位置等。
可作为视频监控系统使用。

三、效果图

四、相关站点

国内站点：https://gitee.com/feiyangqingyun/QWidgetDemo
国际站点：https://github.com/feiyangqingyun/QWidgetDemo
个人主页：https://blog.csdn.net/feiyangqingyun
知乎主页：https://www.zhihu.com/people/feiyangqingyun/
体验地址：https://blog.csdn.net/feiyangqingyun/article/details/97565652

五、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("
", "");
            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;
}

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原文地址：https://www.cnblogs.com/feiyangqingyun/p/13851719.html