Video captured by Media Foundation is vertical mirrorred - c++

Question

I'm using Media Foundation IMFSourceReaderCallback implementation for grabbing video frames from the camera, and then OpenCV imshow to present the frames in a loop.
However I get the frames vertically flipped...
Is this a bug? Should I set some attribute to avoid this?
Here is my code:
Initialization:
IMFAttributes* pDeviceAttrs, *pReaderAttrs;
hr = MFCreateAttributes(&pDeviceAttrs, 1);
if (FAILED(hr)) goto Exit;
hr = pDeviceAttrs->SetGUID(MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE, MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE_VIDCAP_GUID);
if (FAILED(hr)) goto Exit;
//...
// Correct source provider is activated through ActivateObject
//
hr = MFCreateAttributes(&pReaderAttrs, 2);
if (FAILED(hr)) goto Exit;
pReaderAttrs->SetUnknown(MF_SOURCE_READER_ASYNC_CALLBACK,(IUnknown*)this);
pReaderAttrs->SetUINT32(MF_READWRITE_ENABLE_HARDWARE_TRANSFORMS, TRUE);
hr = MFCreateSourceReaderFromMediaSource(pMediaSource, pReaderAttrs, &m_pReader);
if (FAILED(hr)) goto Exit;
// Correct profile is set
OnReadSample implementation:
HRESULT hr = S_OK;
LONG defaultStride = 0;
LONG stride = 0;
BYTE *pBuffer = NULL;
EnterCriticalSection(&m_critSec);
if (NULL != pSample)
{
IMFMediaBuffer* pMediaBuffer;
DWORD dataSize = 0;
// In case of a single buffer, no copy would happen
hr = pSample->ConvertToContiguousBuffer(&pMediaBuffer);
if (FAILED(hr)) goto Cleanup;
pMediaBuffer->GetCurrentLength(&dataSize);
hr = pMediaBuffer->Lock(&pBuffer, &dataSize, &dataSize);
if (FAILED(hr)) goto Cleanup;
// todo: use a backbuffer to avoid sync issues
if (NULL == m_pLatestFrame) m_pLatestFrame = (BYTE*)malloc(dataSize);
memcpy(m_pLatestFrame, pBuffer, dataSize);
++m_frameNumber;
pMediaBuffer->Unlock();
pMediaBuffer->Release();
}
Cleanup:
LeaveCriticalSection(&m_critSec);
// Async ReadFrame for the next buffer:
hr = m_pReader->ReadSample(
(DWORD)MF_SOURCE_READER_FIRST_VIDEO_STREAM,
0,
NULL, // actual
NULL, // flags
NULL, // timestamp
NULL // sample
);
return hr;
Conversion to cv::image:
void SourceReaderImpl::GetLatestFrame(BYTE** ppLatestFrame)
{
EnterCriticalSection(&m_critSec);
*ppLatestFrame = m_pLatestFrame;
LeaveCriticalSection(&m_critSec);
}
void* CameraWrapperImpl::getLatestFrame()
{
BYTE* pLatestFrame = NULL;
m_pMfReader->GetLatestFrame(&pLatestFrame);
return pLatestFrame;
}
void Player::Present()
{
//...
color = cv::Mat(colorSize,
CV_8UC3,
static_cast<unsigned char*>(m_pColorCameraImpl->getLatestFrame()));
cv::imshow(color);
}
Any idea?
Thanks in advance!

Answer 1

A bitmap is stored with the last scan line first, so the image will appear upside down. The easiest solution is to call cv::flip
void Player::Present()
{
//...
color = cv::Mat(colorSize,
CV_8UC3,
static_cast<unsigned char*>(m_pColorCameraImpl->getLatestFrame()));
cv::Mat corrected;
flip(color, corrected, 0);
imshow(corrected);
}