Qt. Why can't convert QVideoFrame to QImage?

Question

Qt

In general, there is a method QVideoFrame::image(), but it appeared only in Qt 5.15 (and I have 5.14.2). But there is an old way with the transfer: a pointer to a byte sequence, width, height, bytes per line and format. This is how I process it:

void MainWindow::processFrame(const QVideoFrame &frame)
{
    QImage image{ frame.bits(), frame.width(), frame.height(), frame.bytesPerLine(),
                  QVideoFrame::imageFormatFromPixelFormat(frame.pixelFormat()) };

    std::clog << frame.width() << " " << frame.height() << "\n"
              << image.width() << " " << image.height() << "\n";

    std::clog << frame.pixelFormat() << "\n"
              << QVideoFrame::imageFormatFromPixelFormat(frame.pixelFormat()) <<"\n";
}

Such a conclusion:

1280 720
0 0
1
5

The format seems to match:

QVideoFrame::Format_ARGB32 == 1
QImage::Format_ARGB32 == 5

I don't understand what could be the problem?

Answer 1

I found out that QVideoFramethere is a method isMapped()that shows whether the frame is located in RAM (or in virtual memory, i.e. whether it is in addressable memory and whether it can be accessed). It turned out that no.
Because the signal QVideoProbe::videoFrameProbed()passes a reference to a constant QVideoFrame, and the function is QVideoFrame::map()not constant, then you need to copy the frame:

void MainWindow::proccessFrame(const QVideoFrame &frame)
{
    QVideoFrame replica = frame;
    replica.map(QAbstractVideoBuffer::ReadOnly);

    std::clog << std::boolalpha << frame.isMapped()   << "\n";
    std::clog << std::boolalpha << replica.isMapped() << "\n";

    QImage image{ replica.bits(), replica.width(),
                  replica.height(), replica.bytesPerLine(),
                  QVideoFrame::imageFormatFromPixelFormat(replica.pixelFormat()) };

    std::clog << replica.width() << " " << replica.height() << "\n";
    std::clog << frame.width()   << " " << frame.height()   << "\n";
    std::clog << image.width()   << " " << image.height()   << "\n";

    std::clog << frame.pixelFormat() << "\n";
    std::clog << QVideoFrame::imageFormatFromPixelFormat(frame.pixelFormat()) << "\n";
}

Answer 2

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