Microsoft Media Foundation Webcam Interface

问题

I've been working on a c++ interface to capture images from all types of webcams via the Micrsoft Media Foundation. I've already got a bit of code that can connect with several types of webcams and is able to capture images in different resolutions and formats.

I know that under WinXP it is possible to change different parameters of the webcam (like white balance, exposure time e.g.) by using the Direct Show library. Unfortunately the interface in the Direct Show library that made it possible to easily capture single frames from a webcam is removed from Direct Show under Win7. Does anybody know how I can acces these parameters using Microsoft Media Foundation or any other library that I can combine with the Microsoft Media Foundation?

回答1:

DirectShow is still good in Windows 7 (the easiest to check is using GraphEdit and AMCap from Windows SDK). Media Foundation however lacks essential support in earlier versions of Windows.

回答2:

It is possible to call a DirectShow QueryInterface method from WMF. Example code is given at Windows Media Foundation: Controlling Camera Properties. This should let you set available camera parameters like focus and white balance etc.

HRESULT CMFVideoCaptureDlg::SetupCamera(IMFMediaSource* pCameraSource) {
    CComQIPtr<IAMCameraControl> spCameraControl(pCameraSource);
    HRESULT hr = S_OK;
    if(spCameraControl) {
        long min, max, step, def, control;
        hr = spCameraControl->GetRange(CameraControl_Exposure, &min, &max, &step, &def, &control);
        if(SUCCEEDED(hr))
            hr = spCameraControl->Set(CameraControl_Exposure, 1, CameraControl_Flags_Manual);
    }
    CComQIPtr<IAMVideoProcAmp> spVideo(pCameraSource);
    if(spVideo)
        hr = spVideo->Set(VideoProcAmp_WhiteBalance, 0, VideoProcAmp_Flags_Auto);
    return hr;
}

It turns out Media Foundation does not define any specific interfaces for these tasks. Curiously enough, it implements interfaces defined by its predecessor, DirectShow, on its media source (represented by the IMFMediaSource interface), when that media source is a video camera

回答3:

This article has the following code and it works like a charm!

HRESULT CMFVideoCaptureDlg::SetupCamera(IMFMediaSource* pCameraSource) {
    CComQIPtr spCameraControl(pCameraSource);
    HRESULT hr = S_OK;
    if(spCameraControl) {
        long min, max, step, def, control;
        hr = spCameraControl->GetRange(CameraControl_Exposure, &min, &max, &step, &def, &control);
        if(SUCCEEDED(hr))
            hr = spCameraControl->Set(CameraControl_Exposure, 1, CameraControl_Flags_Manual);
    }
    CComQIPtr spVideo(pCameraSource);
    if(spVideo)
        hr = spVideo->Set(VideoProcAmp_WhiteBalance, 0, VideoProcAmp_Flags_Auto);
    return hr;
}

回答4:

IAMCameraControl and IANVideoProcAmp still support White balance,pan,zoom in Windows 8. camera control is so far not part of MFT.We have to use Direct Show to do these things.

来源：https://stackoverflow.com/questions/10102843/microsoft-media-foundation-webcam-interface