使用C而不是C ++的Media Foundation [英] Media Foundation using C instead of C++

问题描述

我正在学习使用C而不是C ++从Microsoft网站上显示的示例代码中使用Media Foundation API。示例代码如下所示。

I am learning to use the Media Foundation API from sample code shown in Microsoft website using C instead of C++. The sample code is shown below.

HRESULT CreateVideoCaptureDevice(IMFMediaSource **ppSource)
{
    *ppSource = NULL;

    UINT32 count = 0;

    IMFAttributes *pConfig = NULL;
    IMFActivate **ppDevices = NULL;

    // Create an attribute store to hold the search criteria.
    HRESULT hr = MFCreateAttributes(&pConfig, 1);

    // Request video capture devices.
    if (SUCCEEDED(hr))
    {
        hr = pConfig->SetGUID(
            MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE, 
            MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE_VIDCAP_GUID
            );
    }

    // Enumerate the devices,
    if (SUCCEEDED(hr))
    {
        hr = MFEnumDeviceSources(pConfig, &ppDevices, &count);
    }

    // Create a media source for the first device in the list.
    if (SUCCEEDED(hr))
    {
        if (count > 0)
        {
            hr = ppDevices[0]->ActivateObject(IID_PPV_ARGS(ppSource));
        }
        else
        {
            hr = MF_E_NOT_FOUND;
        }
    }

    for (DWORD i = 0; i < count; i++)
    {
        ppDevices[i]->Release();
    }
    CoTaskMemFree(ppDevices);
    return hr;
}

当我尝试构建示例代码时，总是会出现以下错误：

When I tried to build the sample code, I always get the following error:

错误C2039： ActivateObject：不是 IMFActivate的成员
错误C2039： Release：不是 IMFActivate的成员b $ b错误C2039：'SetGUID'：不是'IMFAttributes'的成员

error C2039: 'ActivateObject': is not a member of 'IMFActivate' error C2039: 'Release': is not a member of 'IMFActivate' error C2039: 'SetGUID': is not a member of 'IMFAttributes'

我浏览了IMFActivate和IMFAttributes的定义（在mfidl.h中），我注意到它具有C风格的界面。

I explored the definition of IMFActivate and IMFAttributes (in mfidl.h) and I notice it have a C style interface.

我可以知道是否有人可以显示如何使用该接口的示例吗？

May I know if anyone can show an example of how to use the interface ?

推荐答案

您应该使用虚拟方法表指针使用定义为 C样式的COM接口：

You should be using COM interfaces defined "C style", using virtual method table pointer:

IMFActivate* pMfActivate = ...
IMFMediaSource* pMfMediaSource;
pMfActivate->lpVtbl->ActivateObject(
    pMfActivate, &IID_IMFMediaSource, (IUnknown**) &pMfMediaSource);

其中C ++风格是

IMFActivate* pMfActivate = ...
IMFMediaSource* pMfMediaSource;
pMfActivate->ActivateObject(
    __uuidof(IMFMediaSource), (IUnknown**) &pMfMediaSource);

这篇关于使用C而不是C ++的Media Foundation的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！