How to QVideoFrame to QImage - qt

Question

The task is to copy a frame from a QVideoFrame, and possibly do something to that Image and displaying the manipulated Image in QML.
...
m_lastFrame = QImage(videoFrame.width(), videoFrame.height(), QImage::Format_ARGB32);
memcpy(m_lastFrame.bits(), videoFrame.bits(),videoFrame.mappedBytes());
...
The above code causes a crash, since m_lastFrame is short of 32 bytes(3686400 vs 3686432)
videoFrame.mappedBytes() reports 3686432 bytes. What am I doing wrong here? Or how should I calculate the size of m_lastFrame().
The code is running on Mac OSx 10.9.5 Qt 5.1.1.
Some additional code:
...
if( videoFrame.map(QAbstractVideoBuffer::ReadOnly) ){
m_lastFrame = QImage(videoFrame.width(),videoFrame.height(),QImage::Format_ARGB32);
memcpy(m_lastFrame.bits(), videoFrame.bits(),videoFrame.mappedBytes() - 32);
...
}
...

Answer 1

Since that doesn't always work, see also comment at convert QVideoFrame to QImage , i.e.
QImage Camera::imageFromVideoFrame(const QVideoFrame& buffer) const
{
QImage img;
QVideoFrame frame(buffer); // make a copy we can call map (non-const) on
frame.map(QAbstractVideoBuffer::ReadOnly);
QImage::Format imageFormat = QVideoFrame::imageFormatFromPixelFormat(
frame.pixelFormat());
// BUT the frame.pixelFormat() is QVideoFrame::Format_Jpeg, and this is
// mapped to QImage::Format_Invalid by
// QVideoFrame::imageFormatFromPixelFormat
if (imageFormat != QImage::Format_Invalid) {
img = QImage(frame.bits(),
frame.width(),
frame.height(),
// frame.bytesPerLine(),
imageFormat);
} else {
// e.g. JPEG
int nbytes = frame.mappedBytes();
img = QImage::fromData(frame.bits(), nbytes);
}
frame.unmap();
return img;
}

Answer 2

You can try creating a QImage by first mapping the QVideoFrame onto a QAbstractVideoBuffer in the following way :
bool CameraFrameGrabber::present(const QVideoFrame &frame)
{
Q_UNUSED(frame);
if (frame.isValid()) {
QVideoFrame cloneFrame(frame);
cloneFrame.map(QAbstractVideoBuffer::ReadOnly);
const QImage image(cloneFrame.bits(),
cloneFrame.width(),
cloneFrame.height(),
QVideoFrame::imageFormatFromPixelFormat(cloneFrame .pixelFormat()));
emit frameAvailable(image);
qDebug()<<cloneFrame.mappedBytes();
cloneFrame.unmap();
return true;
}
If you want QImage in any other format just change the last parameter during creating the image, to the whichever format you like :
QImage::Format_xxx ;
instead of
QVideoFrame::imageFormatFromPixelFormat(cloneFrame .pixelFormat()));