videoio: MSMF async reader for camera stream

Synchronized reading from camera with heavy frame processing
provides bad effects (huge frame latency, processing frames from the past).
Generally, there is no way to process each frame and some frames will be dropped.
Allow preventive frame dropping to reduce lag of processed frames.

This mode is applied to cameras only (opened by 'index').

modules/videoio/src/cap_msmf.cpp

@@ -93,6 +93,8 @@
 
 #include <comdef.h>
 
+#include <shlwapi.h>  // QISearch
+
 struct IMFMediaType;
 struct IMFActivate;
 struct IMFMediaSource;
@@ -595,6 +597,77 @@ void MediaType::Clear()
 
 }
 
+class SourceReaderCB : public IMFSourceReaderCallback
+{
+public:
+    SourceReaderCB() :
+        m_nRefCount(1), m_hEvent(CreateEvent(NULL, FALSE, FALSE, NULL)), m_bEOS(FALSE), m_hrStatus(S_OK), m_dwStreamIndex(0)
+    {
+    }
+
+    // IUnknown methods
+    STDMETHODIMP QueryInterface(REFIID iid, void** ppv) CV_OVERRIDE
+    {
+#ifdef _MSC_VER
+#pragma warning(push)
+#pragma warning(disable:4838)
+#endif
+        static const QITAB qit[] =
+        {
+            QITABENT(SourceReaderCB, IMFSourceReaderCallback),
+            { 0 },
+        };
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif
+        return QISearch(this, qit, iid, ppv);
+    }
+    STDMETHODIMP_(ULONG) AddRef() CV_OVERRIDE
+    {
+        return InterlockedIncrement(&m_nRefCount);
+    }
+    STDMETHODIMP_(ULONG) Release() CV_OVERRIDE
+    {
+        ULONG uCount = InterlockedDecrement(&m_nRefCount);
+        if (uCount == 0)
+        {
+            delete this;
+        }
+        return uCount;
+    }
+
+    STDMETHODIMP OnReadSample(HRESULT hrStatus, DWORD dwStreamIndex, DWORD dwStreamFlags, LONGLONG llTimestamp, IMFSample *pSample) CV_OVERRIDE;
+    STDMETHODIMP OnEvent(DWORD, IMFMediaEvent *) CV_OVERRIDE
+    {
+        return S_OK;
+    }
+    STDMETHODIMP OnFlush(DWORD) CV_OVERRIDE
+    {
+        return S_OK;
+    }
+
+    HRESULT Wait(DWORD dwMilliseconds, _ComPtr<IMFSample>& videoSample, BOOL& pbEOS);
+
+private:
+    // Destructor is private. Caller should call Release.
+    virtual ~SourceReaderCB()
+    {
+        CV_LOG_WARNING(NULL, "terminating async callback");
+    }
+
+public:
+    long                m_nRefCount;        // Reference count.
+    cv::Mutex           m_mutex;
+    HANDLE              m_hEvent;
+    BOOL                m_bEOS;
+    HRESULT             m_hrStatus;
+
+    _ComPtr<IMFSourceReader> m_reader;
+    DWORD m_dwStreamIndex;
+    _ComPtr<IMFSample>  m_lastSample;
+};
+
+
 /******* Capturing video from camera or file via Microsoft Media Foundation **********/
 class CvCapture_MSMF : public cv::IVideoCapture
 {
@@ -643,6 +716,7 @@ protected:
     _ComPtr<IMFSample> videoSample;
     LONGLONG sampleTime;
     bool isOpen;
+    _ComPtr<IMFSourceReaderCallback> readCallback;  // non-NULL for "live" streams (camera capture)
 };
 
 CvCapture_MSMF::CvCapture_MSMF():
@@ -686,6 +760,7 @@ void CvCapture_MSMF::close()
         camid = -1;
         filename.clear();
     }
+    readCallback.Release();
 }
 
 bool CvCapture_MSMF::configureHW(bool enable)
@@ -887,6 +962,14 @@ bool CvCapture_MSMF::open(int _index)
                             if (D3DMgr)
                                 srAttr->SetUnknown(MF_SOURCE_READER_D3D_MANAGER, D3DMgr.Get());
 #endif
+                            readCallback = ComPtr<IMFSourceReaderCallback>(new SourceReaderCB());
+                            HRESULT hr = srAttr->SetUnknown(MF_SOURCE_READER_ASYNC_CALLBACK, (IMFSourceReaderCallback*)readCallback.Get());
+                            if (FAILED(hr))
+                            {
+                                readCallback.Release();
+                                continue;
+                            }
+
                             if (SUCCEEDED(MFCreateSourceReaderFromMediaSource(mSrc.Get(), srAttr.Get(), &videoFileSource)))
                             {
                                 isOpen = true;
@@ -958,10 +1041,116 @@ bool CvCapture_MSMF::open(const cv::String& _filename)
     return isOpen;
 }
 
+
+HRESULT SourceReaderCB::Wait(DWORD dwMilliseconds, _ComPtr<IMFSample>& videoSample, BOOL& bEOS)
+{
+    bEOS = FALSE;
+
+    DWORD dwResult = WaitForSingleObject(m_hEvent, dwMilliseconds);
+    if (dwResult == WAIT_TIMEOUT)
+    {
+        return E_PENDING;
+    }
+    else if (dwResult != WAIT_OBJECT_0)
+    {
+        return HRESULT_FROM_WIN32(GetLastError());
+    }
+
+    if (!bEOS)
+    {
+        cv::AutoLock lock(m_mutex);
+        bEOS = m_bEOS;
+        if (!bEOS)
+        {
+            videoSample = m_lastSample;
+            CV_Assert(videoSample);
+            m_lastSample.Release();
+            ResetEvent(m_hEvent);  // event is auto-reset, but we need this forced reset due time gap between wait() and mutex hold.
+        }
+    }
+
+    return m_hrStatus;
+}
+
+STDMETHODIMP SourceReaderCB::OnReadSample(HRESULT hrStatus, DWORD dwStreamIndex, DWORD dwStreamFlags, LONGLONG llTimestamp, IMFSample *pSample)
+{
+    CV_UNUSED(llTimestamp);
+
+    HRESULT hr = 0;
+    cv::AutoLock lock(m_mutex);
+
+    if (SUCCEEDED(hrStatus))
+    {
+        if (pSample)
+        {
+            CV_LOG_DEBUG(NULL, "videoio(MSMF): got frame at " << llTimestamp);
+            IMFSample* prev = m_lastSample.Get();
+            if (prev)
+            {
+                CV_LOG_DEBUG(NULL, "videoio(MSMF): drop frame (not processed)");
+            }
+            m_lastSample = pSample;
+        }
+    }
+    else
+    {
+        CV_LOG_WARNING(NULL, "videoio(MSMF): OnReadSample() is called with error status: " << hrStatus);
+    }
+
+    if (MF_SOURCE_READERF_ENDOFSTREAM & dwStreamFlags)
+    {
+        // Reached the end of the stream.
+        m_bEOS = true;
+    }
+    m_hrStatus = hrStatus;
+
+    if (FAILED(hr = m_reader->ReadSample(dwStreamIndex, 0, NULL, NULL, NULL, NULL)))
+    {
+        CV_LOG_WARNING(NULL, "videoio(MSMF): async ReadSample() call is failed with error status: " << hr);
+        m_bEOS = true;
+    }
+
+    if (pSample || m_bEOS)
+    {
+        SetEvent(m_hEvent);
+    }
+    return S_OK;
+}
+
+
 bool CvCapture_MSMF::grabFrame()
 {
     CV_TRACE_FUNCTION();
-    if (isOpen)
+    if (readCallback)  // async "live" capture mode
+    {
+        HRESULT hr = 0;
+        SourceReaderCB* reader = ((SourceReaderCB*)readCallback.Get());
+        if (!reader->m_reader)
+        {
+            // Initiate capturing with async callback
+            reader->m_reader = videoFileSource;
+            reader->m_dwStreamIndex = dwStreamIndex;
+            if (FAILED(hr = videoFileSource->ReadSample(dwStreamIndex, 0, NULL, NULL, NULL, NULL)))
+            {
+                CV_LOG_ERROR(NULL, "videoio(MSMF): can't grab frame - initial async ReadSample() call failed: " << hr);
+                reader->m_reader = NULL;
+                return false;
+            }
+        }
+        BOOL bEOS = false;
+        if (FAILED(hr = reader->Wait(10000, videoSample, bEOS)))  // 10 sec
+        {
+            CV_LOG_WARNING(NULL, "videoio(MSMF): can't grab frame. Error: " << hr);
+            return false;
+        }
+        if (bEOS)
+        {
+            CV_LOG_WARNING(NULL, "videoio(MSMF): EOS signal. Capture stream is lost");
+            return false;
+        }
+        return true;
+    }
+    else if (isOpen)
     {
         DWORD streamIndex, flags;
         videoSample.Release();