Handling Repaint Events in Video Capture (Windows Embedded CE 6.0)
1/6/2010
If you build a video capture graph without using the ICaptureGraphBuilder2 interface, and you preview the video using the old DirectShow Video Renderer filter, then you should override the default handling for EC_REPAINT events. Query the Filter Graph Manager for the IMediaEvent Interface and call the IMediaEvent::CancelDefaultHandling method with the value EC_REPAINT:
IMediaEvent *pEvent = 0;
hr = pGraph->QueryInterface(IID_IMediaEvent, (void**)&pEvent);
if (SUCCEEDED(hr))
{
pEvent->CancelDefaultHandling (EC_REPAINT);
pEvent->Release();
}
This prevents a possible error that can corrupt your capture file. If the user covers and uncovers the preview window, the Video Renderer filter receives a WM_PAINT message. By default, the Video Renderer requests a new frame, and the Filter Graph Manager pauses the graph in order to cue another video frame. If that happens while the graph is writing a file, it will corrupt the file. Overriding the default EC_REPAINT behavior prevents the renderer from requesting a new frame.
You do not have to perform this step if you are using the ICaptureGraphBuilder2 interface, because the Capture Graph Builder does it for you automatically.