DirectShow中通过IAMStreamSelect接口实现多音轨切换

IAMStreamSelect 接口

(只有英文版的，中文搜索起来不方便，MSDN中文版翻译太慢，故写之，转载时请注明，源自vcmute)
IAMStreamSelect 接口控制哪些流被播放并获取他们的信息. 典型的应用是不用的语言编码的一套音频流之间的选择. 举例来说, 用户可选择在英语、德语和法语间切换音轨，所以在MediaPlayer音频和语言音轨切换是同一菜单项.

方法	描述
Count	得到有效流的总数.
Info	获取一个指定流的信息.
Enable	使能或禁止一个指定流.

示例

下面例子讲述如何使用IAMStreamSelect 接口, 获取流的信息, 使能指定流, 并显示对应信息.
该例子假设播放文件存在 C:/Sami_test_file.sami.并使用固定索引1和3来调用Enable函数:

void __cdecl main()
{
    HRESULT hr;
    IGraphBuilder *pGraph;
    IMediaControl *pMediaControl;
    IMediaEventEx *pEv;
    IBaseFilter   *pSAMI;

    CoInitialize(NULL);
    
    // 创建 filter graph manager.
    CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC, 
                        IID_IGraphBuilder, (void **)&pGraph);
    pGraph->QueryInterface(IID_IMediaControl, (void **)&pMediaControl);
    pGraph->QueryInterface(IID_IMediaEventEx, (void**)&pEv);

    // 建立 graph 并寻找 SAMI parser.
    pGraph->RenderFile(L"C://Sami_test_file.sami", NULL);
    hr = pGraph->FindFilterByName(L"SAMI (CC) Parser", &pSAMI);
    if (SUCCEEDED(hr)) 
    {
        *pStrm = NULL;
        hr = pSAMI->QueryInterface(IID_, (void**)&pStrm);
        if (SUCCEEDED(hr)) 
        {
            DWORD dwStreams = 0;
            pStrm->Count(&dwStreams);
            printf("Stream count: %d/n", dwStreams);

            // 选择流1和流3(French 和 "GreenText")
            hr = pStrm->Enable(1, AMSTREAMSELECTENABLE_ENABLE);
            hr = pStrm->Enable(3, AMSTREAMSELECTENABLE_ENABLE);

            // 打印各个流的信息
            for (DWORD index = 0; index < dwStreams; index++)
            {
                DWORD dwFlags;
                WCHAR *wszName;
                hr = pStrm->Info(index, NULL, &dwFlags, NULL, NULL, &wszName, NULL, NULL);
                wprintf(L"Stream %d: %s [%s]/n", index, wszName, 
                    (dwFlags ?  L"ENABLED" : L"DISABLED"));
                CoTaskMemFree(wszName);
            }
            pStrm->Release();
        }
        pSAMI->Release();
    }

    // 播放
    pMediaControl->Run();
    while (1)
    {
        long evCode, lParam1, lParam2;
        pEv->GetEvent(&evCode, &lParam1, &lParam2, 100);
        
        if (evCode == EC_OLE_EVENT) {
            wprintf(L"%s/n", (BSTR)lParam2);
        }
        pEv->FreeEventParams(evCode, lParam1, lParam2);

        if (evCode == EC_USERABORT || evCode == EC_COMPLETE || evCode == EC_ERRORABORT)
            break;
    }

    // 释放.
    pMediaControl->Release();
    pEv->Release();
    pGraph->Release();
    CoUninitialize();
}

注：有些切换器如MMSwitch只能在运行中切换，所以在切换前要加一句 pMediaControl->Pause();