Map cv::Mat to QAbstractPlanarVideoBuffer subclass

Konrad Matusiak

Im trying to map a cv::Mat to QAbstractPlanarVideoBuffer and then to QVideoFrame.
A conversion from cv::Mat to QImage and then to QVideoFrame is to slow for my use case.
The following code produces mostly green frames. I have no experience with video encoding so I don't know what the problem could be. Any help would be appreciated. Thanks in advance.

CVBuffer.h:

#ifndef CVBUFFER_H
#define CVBUFFER_H

#include <QAbstractPlanarVideoBuffer>
#include "opencv2/core.hpp"
#include "opencv2/imgproc.hpp"
#include "opencv2/calib3d.hpp"

class CVBuffer : public QAbstractPlanarVideoBuffer
{

public:
    CVBuffer(cv::Mat *frame);
    ~CVBuffer();

    int map(MapMode mode, int *numBytes, int bytesPerLine[4], uchar *data[4]);

    MapMode mapMode() const;

    void unmap();
private:
    cv::Mat frame;

};
#endif // CVBUFFER_H

CVBuffer.cpp

#include "cvbuffer.h"

CVFBuffer::FBuffer(cv::Mat* frame)
     : QAbstractPlanarVideoBuffer(NoHandle)
     , frame(frame->clone())
 {
 }

 CVBuffer::~CVBuffer() {
 }

 int FBuffer::map(MapMode mode, int *numBytes, int bytesPerLine[4], uchar *data[4]) {
     if (mode == ReadOnly) {
          *numBytes = frame.total() * frame.elemSize();
         bytesPerLine[0] = frame.step;
         data[0] = frame.data;
         return 3;
     }
     return 0;
 }

 FBuffer::MapMode FBuffer::mapMode() const { return ReadOnly; }

 void FBuffer::unmap() { }

Christian Ehrlicher

Why to you return 3? I only see that you have one plane.
Also you should free/unref your frame in the dtor

Bonnie

I have no experience in this but it may help to look at how Qt use gstreamer's video frame to construct a planar video buffer:
https://code.woboq.org/qt5/qtmultimedia/src/gsttools/qgstvideobuffer.cpp.html