Qt获取摄像头画面的每一帧数据

继承自QAbstractVideoSurface，实现它的一些虚函数，可以在实现的虚函数 present 中获取到摄像头画面的一帧数据，拿到数据之后就可以转换处理了，这里拿到数据之后，绘制在主窗口上了。
主要代码：
首先在 .pro 中加入 multimedia 模块:

QT += core gui multimedia multimediawidgets

MainWindow.cpp

#include "MainWindow.h"
#include "ui_MainWindow.h"
#include <QtWidgets>
#include <QVideosurfaceFormat>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    camera_ = new QCamera;
    surface_ = new MyVideoSurface(this);
    camera_->setViewfinder(surface_);
    camera_->start();//这里启动
}

MainWindow::~MainWindow()
{
    delete ui;
}

QSize MainWindow::sizeHint() const
{
    return surface_->surfaceFormat().sizeHint();
}

void MainWindow::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    if (surface_->isActive()) {
        const QRect videoRect = surface_->videoRect();
        if (!videoRect.contains(event->rect())) {
            QRegion region = event->region();
            region = region.subtracted(videoRect);
            QBrush brush = palette().background();
            for (const QRect &rect : region){
                painter.fillRect(rect, brush);
            }
        }
        surface_->paint(&painter);//在主窗口绘制
    } else {
        painter.fillRect(event->rect(), palette().background());
    }
}

void MainWindow::resizeEvent(QResizeEvent *event)
{
    QMainWindow::resizeEvent(event);
    surface_->updateVideoRect();
}

MyVideoSurface.h

#ifndef MYVIDEOSURFACE_H
#define MYVIDEOSURFACE_H

#include <QAbstractVideoSurface>
#include <QImage>
#include <QRect>
#include <QVideoFrame>

class MyVideoSurface : public QAbstractVideoSurface
{
    Q_OBJECT

public:
    MyVideoSurface(QWidget *widget, QObject *parent = 0);
    QList<QVideoFrame::PixelFormat> supportedPixelFormats(QAbstractVideoBuffer::HandleType handleType = QAbstractVideoBuffer::NoHandle) const override;
    bool isFormatSupported(const QVideoSurfaceFormat &format) const override;
    bool start(const QVideoSurfaceFormat &format) override;
    bool present(const QVideoFrame &frame) override;
    void stop() override;
    QRect videoRect() const;
    void updateVideoRect();
    void paint(QPainter *painter);

private:
    QWidget * widget_;
    QImage::Format imageFormat_;
    QRect targetRect_;
    QSize imageSize_;
    QVideoFrame currentFrame_;
};

#endif

MyVideoSurface.cpp

#include "MyVideoSurface.h"

#include <QtWidgets>
#include <qabstractvideosurface.h>
#include <qvideosurfaceformat.h>
#include <QVideoSurfaceFormat>

MyVideoSurface::MyVideoSurface(QWidget *widget, QObject *parent)
    : QAbstractVideoSurface(parent)
    , widget_(widget)
    , imageFormat_(QImage::Format_Invalid)
{
}

QList<QVideoFrame::PixelFormat> MyVideoSurface::supportedPixelFormats(QAbstractVideoBuffer::HandleType handleType) const
{
    if (handleType == QAbstractVideoBuffer::NoHandle) {
        return QList<QVideoFrame::PixelFormat>()<< QVideoFrame::Format_RGB32<< QVideoFrame::Format_ARGB32<< QVideoFrame::Format_ARGB32_Premultiplied<< QVideoFrame::Format_RGB565<< QVideoFrame::Format_RGB555;
    } else {
        return QList<QVideoFrame::PixelFormat>();
    }
}

bool MyVideoSurface::isFormatSupported(const QVideoSurfaceFormat & format) const
{
    return QVideoFrame::imageFormatFromPixelFormat(format.pixelFormat()) != QImage::Format_Invalid && !format.frameSize().isEmpty() && format.handleType() == QAbstractVideoBuffer::NoHandle;
}

bool MyVideoSurface::start(const QVideoSurfaceFormat &format)
{
    const QImage::Format imageFormat_ = QVideoFrame::imageFormatFromPixelFormat(format.pixelFormat());
    const QSize size = format.frameSize();
    if (imageFormat_ != QImage::Format_Invalid && !size.isEmpty()) {
        this->imageFormat_ = imageFormat_;
        widget_->resize(size);
        QAbstractVideoSurface::start(format);
        widget_->updateGeometry();
        updateVideoRect();
        return true;
    }
    return false;
}

void MyVideoSurface::stop()
{
    currentFrame_ = QVideoFrame();
    targetRect_ = QRect();
    QAbstractVideoSurface::stop();
    widget_->update();
}

bool MyVideoSurface::present(const QVideoFrame &frame) //每一帧摄像头的数据，都会经过这里
{
    if (surfaceFormat().pixelFormat() != frame.pixelFormat() || surfaceFormat().frameSize() != frame.size()) {
        setError(IncorrectFormatError);
        stop();
        return false;
    }
    currentFrame_ = frame;
    widget_->repaint(targetRect_);
    return true;
}

QRect MyVideoSurface::videoRect() const
{
    return targetRect_;
}

void MyVideoSurface::updateVideoRect()
{
    QSize size = surfaceFormat().sizeHint();
    size.scale(widget_->size().boundedTo(size), Qt::KeepAspectRatio);
    targetRect_ = QRect(QPoint(0, 0), size);
    targetRect_.moveCenter(widget_->rect().center());
}

void MyVideoSurface::paint(QPainter *painter)//这里绘制每一帧数据
{
    if (currentFrame_.map(QAbstractVideoBuffer::ReadOnly)) {
        //img就是转换的数据了
        QImage img = QImage(currentFrame_.bits(),currentFrame_.width(),currentFrame_.height(),currentFrame_.bytesPerLine(),imageFormat_).mirrored(true,false).scaled(widget_->size());
        painter->drawImage(targetRect_, img, QRect(QPoint(0,0),img.size()));
        currentFrame_.unmap();
    }
}

效果：