一、通过V4l2来采集用qt显示

1.将V4L2获取摄像头数据封装成一个类

class V4L2API
{
public:
    explicit V4L2API(const char *dev="/dev/video0");
    ~V4L2API();

    int video_init();//打开设备、设置采集格式等
    int video_start();//开始采集
    int video_stop();//停止采集
    int video_getframe(char *buffer, int *size);//读数据
    int video_destroy();//释放空间、关闭设备
    bool yuv422torgb24(unsigned char *buffer, unsigned char *rgbdata, int w, int h);//将YUV数据转化为RGB数据

private:
    int fd;
    char dev[64];
    unsigned char *mmps[4];//保存映射空间首地址
    unsigned int mmpsize[4];
};
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2.设置开始按钮开始采集数据

void V4L2Win::on_startbt_clicked()
{
    if(v4l2api == nullptr)
    {
        v4l2api = new V4L2API("/dev/video0");//初始化摄像头对象
    }
    v4l2api->video_start();//开始采集
    //启动定时器，开始采集
    mtimer.start(100);
}
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3.设置停止按钮停止采集数据

void V4L2Win::on_stopbt_clicked()
{
    //停止定时器
    mtimer.stop();
    if(v4l2api != nullptr)
    {
        v4l2api->video_stop();//停止采集
        v4l2api->video_destroy();
        delete v4l2api;
        v4l2api = nullptr;
    }
}
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4.设置定时器不断采集数据

connect(&mtimer,&QTimer::timeout,this,&V4L2Win::get_frame);
void V4L2Win::get_frame()
{
    v4l2api->video_getframe(buffer,&size); //得到的是YUYV--4:2:2
    v4l2api->yuv422torgb24((unsigned char*)buffer, (unsigned char*)rgbdata, 640, 480); //把yuv4:2:2 转RGB

    QImage image((uchar*)rgbdata,640,480,QImage::Format_RGB888);
    ui->label->setPixmap(QPixmap::fromImage(image));
}
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二、直接用qt多媒体模块来实现采集并且显示

1.在qt工程文件中添加

QT += multimedia
QT += multimediawidgets
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QCamera  --摄像头设备
QCameraViewfinder--预览显示
QCameraImageCapture--数据抓取
QCameraInfo---摄像头信息
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2.获取系统所有摄像头设备

Cameralist = QCameraInfo::availableCameras();
foreach (QCameraInfo info, Cameralist)
{
    qDebug()<<info.position()<<info.deviceName();
    ui->comboBox->addItem(info.description());
}
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3.开启摄像头并且显示预览

QCameraInfo info = Cameralist.at(ui->comboBox->currentIndex()); //获取一个摄像头信息
camera = new QCamera(info);//通过摄像头信息创建设备
viewFinder = new QCameraViewfinder(ui->cameraView);//创建一个预览窗口
camera->setViewfinder(viewFinder);
viewFinder->resize(ui->cameraView->size());
viewFinder->show();
camera->start();//开始
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4.初始化抓取数据的对象

imageCap = new QCameraImageCapture(camera);
    connect(imageCap,&QCameraImageCapture::imageCaptured,this,&ModelWin::get_frame);
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5.发送抓取数据的信号

filename = QFileDialog::getSaveFileName(this);//选择文件存放的路径
imageCap->capture();//发送一个信号
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6.数据抓取

image.save(filename);
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