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，原文地址 http://blog.csdn.net/vcmute/archive/2005/10/16/504909.aspx)

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))
{
IAMStreamSelect *pStrm = NULL;
hr = pSAMI->QueryInterface(IID_IAMStreamSelect, (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();