Cannot write to QVideoFrame from QVideoFilterRunnable [ubuntu 18]

mikeitexpert

I am trying the change QVideoFrame from QVideoFilterRunnable but it doesn't allow me (see below):

I am running the code on Ubuntu 18.

16:38:27: Starting /home/mike/Downloads/OpticalMeasure/build-CuteDetector-Desktop_Qt_5_12_0_GCC_64bit-Debug/CuteDetector...
QML debugging is enabled. Only use this in a safe environment.

(CuteDetector:17368): GStreamer-CRITICAL **: 16:38:29.127: write map requested on non-writable buffer
16:38:29: The program has unexpectedly finished.

qcvdetectfilter.h

#ifndef QCVDETECTFILTER_H
#define QCVDETECTFILTER_H

#include <QAbstractVideoFilter>
#include <QDebug>
#include <QTemporaryFile>
#include <QMutex>
#include "opencv2/opencv.hpp"

class QCvDetectFilter : public QAbstractVideoFilter
{
    Q_OBJECT
public:
    QVideoFilterRunnable *createFilterRunnable();

signals:
    void objectDetected(float x, float y, float w, float h);

public slots:

};

class QCvDetectFilterRunnable : public QVideoFilterRunnable
{
public:
    QCvDetectFilterRunnable(QCvDetectFilter *creator) {filter = creator;}
    QVideoFrame run(QVideoFrame *input, const QVideoSurfaceFormat &surfaceFormat, RunFlags flags);

private:
    void dft(cv::InputArray input, cv::OutputArray output);
    QCvDetectFilter *filter;
};

#endif // QCVDETECTFILTER_H

qcvdetectfilter.cpp

#include "qcvdetectfilter.h"
#include "cvmatandqimage.h"

cv::CascadeClassifier classifier;

QVideoFilterRunnable* QCvDetectFilter::createFilterRunnable()
{
    return new QCvDetectFilterRunnable(this);
}

QVideoFrame QCvDetectFilterRunnable::run(QVideoFrame *input, const QVideoSurfaceFormat &surfaceFormat, RunFlags flags)
{
    Q_UNUSED(flags);
    input->map(QAbstractVideoBuffer::WriteOnly);

//    if( input->isValid() && input->map(QAbstractVideoBuffer::ReadWrite))
//       {
        cv::Mat mat(input->height(),input->width(), CV_8U, input->bits());
        cv::Scalar color(255, 0, 0);
        cv::circle(mat, cv::Point(50,50), 20, color);

 input->unmap();
    return *input;
}

SGaist

Hi,

Why did you remove the check of the return value of map ?

mikeitexpert

hi,

Cuz even if I keep it like below, I still get the same error message:

if( input->isValid() && input->map(QAbstractVideoBuffer::ReadWrite))
       {
        input->bits()[0] = 1;
        cv::Mat mat(input->height(),input->width(), CV_8U, input->bits());
        cv::Scalar color(255, 0, 0);
        cv::circle(mat, cv::Point(50,50), 20, color);
    } else {
        std::cout << "is not writable";
    }

here is the error


(CuteDetector:5644): GStreamer-CRITICAL **: 04:06:49.253: write map requested on non-writable buffer
QVideoFrame::unmap() was called more times then QVideoFrame::map()

I found a working example which does the job pretty perfectly but I have hard time figuring out what is actually done differently.

At least let me know how things done differently here :)

https://github.com/stephenquan/MyVideoFilterApp

SGaist

He never maps the QVideoFrame directly.

He either us the private qt_imageFromVideoFrame method (which will to the map/unmap cycle) to get a QImage and work on that, or in the case of an OpenGL Texture, use OpenGL directly to access the data.