QT对摄像头支持

Qt从5.0开始支持android摄像头，但是目前还没有做到统一完全跨平台API。还需要根据不同的平台系统来处理。这是因为Qt中QImage支持格式不全，现在不支持YUV格式。

Qt中捕获视频流用两种方式：

一、用QCamera::setViewfinder(QAbstractVideoSurface *surface)

class MyVideoSurface : public QAbstractVideoSurface
{
    QList<QVideoFrame::PixelFormat> supportedPixelFormats(
            QAbstractVideoBuffer::HandleType handleType = QAbstractVideoBuffer::NoHandle) const
    {
        Q_UNUSED(handleType);

        // 返回你将处理的格式
        return QList<QVideoFrame::PixelFormat>() << QVideoFrame::Format_RGB32;
    }

    bool present(const QVideoFrame &frame)
    {
        Q_UNUSED(frame);
        // 处理捕获的帧
        return true;
    }
};

二、用QVideoProbe

camera = new QCamera;
viewfinder = new QCameraViewfinder();
camera->setViewfinder(viewfinder);

camera->setCaptureMode(QCamera::CaptureVideo);

videoProbe = new QVideoProbe(this);

if (videoProbe->setSource(camera)) {
    // Probing succeeded, videoProbe->isValid() should be true.
    connect(videoProbe, SIGNAL(videoFrameProbed(QVideoFrame)),
            this, SLOT(detectBarcodes(QVideoFrame)));
}

camera->start();
// Viewfinder frames should now also be emitted by
// the video probe, even in still image capture mode.
// Another alternative is to install the probe on a
// QMediaRecorder connected to the camera to get the
// recorded frames, if they are different from the
// viewfinder frames.

 

windows实现了第一种方式，android实现了第二种方式。

windows支持格式为RGB24、RGB32；android支持格式为NV21

 

下面我对捕获和显示进行了封装：

CaptureVideoFrame.h

/*
 * 作者：康林(msn、email: [email protected])
 *
 * 从摄像头（QCarmera）或者（Player）中捕获视频帧。
 * 注意：android后景摄像头捕获的视频翻转-90度，前景摄像头翻转90度。
 * 用法：
 *      QCamera m_Camera;
 *      m_Camera.setCaptureMode(QCamera::CaptureVideo);
 *      CCaptureVideoFrame videoFrame;
 *      videoFrame.setSource(&m_Camera);
 * 注册SLOT：
 *      connect(&videoFrame, SIGNAL(CaptureFrame(const QVideoFrame&)),
 *           SLOT(CaptureVideoFrame(const QVideoFrame&)));
 * 在SLOT 中 CaptureVideoFrame(const QVideoFrame&) 处理捕获到的视频帧。
 *
 * 示例代码：
 *   QList<QByteArray> device = QCamera::availableDevices();
 *   QList<QByteArray>::iterator it;
 *   for(it = device.begin(); it != device.end(); it++)
 *   {
 *       qDebug("Camera:%s", qPrintable(QCamera::deviceDescription(*it)));
 *   }
 *
 *   QCamera camera(QCamera::availableDevices().at(1));
 *   camera.setCaptureMode(QCamera::CaptureVideo);
 *   CFrmPlayer player;
 *   CCaptureVideoFrame captureVideoFrame;
 *   if(captureVideoFrame.setSource(&camera))
 *   {
 *       qDebug("probe.setSource is ok");
 *       player.connect(&captureVideoFrame, SIGNAL(CaptureFrame(QVideoFrame)),
 *                      SLOT(present(QVideoFrame)));
 *   }
 *
 *   player.show();
 *   player.activateWindow();
 *   camera.start();
 */

#ifndef CAPTUREVIDEOFRAME_H
#define CAPTUREVIDEOFRAME_H

#include <QAbstractVideoSurface>
#include <QVideoProbe>
#include <QCamera>

class CCaptureVideoFrame : public QAbstractVideoSurface
{
    Q_OBJECT
public:
    explicit CCaptureVideoFrame(QObject *parent = 0);

    virtual QList<QVideoFrame::PixelFormat> supportedPixelFormats(
            QAbstractVideoBuffer::HandleType handleType = QAbstractVideoBuffer::NoHandle) const;

    bool setSource(QCamera *pCamera);

signals:
    //视频帧捕获信号
    void CaptureFrame(const QVideoFrame &frame);

private slots:
    virtual bool present(const QVideoFrame &frame);

private:
     QVideoProbe m_Probe;//android下,目前只能用probe捕获视频

};

#endif // CAPTUREVIDEOFRAME_H

CaptureVideoFrame.cpp

/** 作者：康林(msn、email: [email protected])*/
#include "CaptureVideoFrame.h"
#include <QCamera>

CCaptureVideoFrame::CCaptureVideoFrame(QObject *parent) :
    QAbstractVideoSurface(parent)
{
}

QList<QVideoFrame::PixelFormat> CCaptureVideoFrame::supportedPixelFormats(QAbstractVideoBuffer::HandleType handleType) const
{
    Q_UNUSED(handleType);
    QList<QVideoFrame::PixelFormat> lst;

    //lst.push_back(QVideoFrame::Format_YUYV);//Qt现在不支持此格式，因为Qt内部用了QImage来处理视频帧。
    lst.push_back(QVideoFrame::Format_RGB32);
    lst.push_back(QVideoFrame::Format_BGR32);

    return lst;
}

//捕获视频帧。windows下格式是RGB32；android下是NV21
bool CCaptureVideoFrame::present(const QVideoFrame &frame)
{
    qDebug("CCaptureVideoFrame::present format:%d", frame.pixelFormat());
    emit CaptureFrame(frame);

    return true;
}

//根据不同的平台，设置捕获方式
bool CCaptureVideoFrame::setSource(QCamera *pCamera)
{
    bool ret = true;
#ifdef ANDROID
    //android下,目前只能用probe捕获视频
    ret = m_Probe.setSource(pCamera);
    if(ret)
    {
        connect(&m_Probe, SIGNAL(videoFrameProbed(QVideoFrame)),
                          SLOT(present(QVideoFrame)));
    }
#else
    //windows下,只能用下面方式捕获视频
    pCamera->setViewfinder(this);
#endif
    return ret;
}

 注意：android使用时需要定义 ANDROID 宏

 

QT对摄像头的支持存在的一些问题：

QT得到到捕获帧相关的参数

QT 在windows、linux下捕获视频只有5帧/秒左右，在我的电脑上用时 240ms 左右。在Android手机上可达到15帧/s（60ms左右）。

QT 在 windows、linux下多个摄像头切换正常，但在 android 手机上，前后摄像头不能切换。代码如下：

void CFrmVideo::on_cmbCamera_currentIndexChanged(int index)
{
    LOG_MODEL_DEBUG("Video", "CFrmVideo::on_cmbCamera_currentIndexChanged");

    m_CameraPostition = QCamera::availableDevices().at(index);

    OpenCamera();
    LOG_MODEL_DEBUG("Video", "CFrmVideo::on_cmbCamera_currentIndexChanged end");
}

int CFrmVideo::OpenCamera()
{
    if(!m_pCall)
    {
        LOG_MODEL_ERROR("Video", "CFrmVideo::OpenCamera m_pCall is null");
        return -1;
    }

    if(m_pCamera)
    {
        CloseCamera();
    }

    m_pCamera = new QCamera(m_CameraPostition);
    if(!m_pCamera)
    {
        LOG_MODEL_WARNING("Video", "Open carmera fail");
        return -1;
    }

    m_pCamera->setCaptureMode(QCamera::CaptureVideo);
    m_CaptureVideoFrame.setSource(m_pCamera);

    //m_pCamera->load();
    m_pCamera->start();
    return 0;
}

int CFrmVideo::CloseCamera()
{
    if(m_pCamera)
    {
        m_pCamera->stop();
        //m_pCamera->unload();
        delete m_pCamera;
        m_pCamera = NULL;
    }
    return 0;
}