Using IAMStreamSelect To Select a Specific Audio Stream from an MPEG File

The IAMStreamSelect is a Direct Show interface for selecting which streams are played and retrieving information about them. An example of logical stream selection would be selecting a particular language (English, German, or French for example) from a set of audio streams that encode different national languages.

To use IAMStreamSelect to select a specific audio stream from an MPEG file with multiple audio streams, perform the following steps:

1. Create an instance of ltmmPlay class:

C Source

IltmmPlay* pPlay; 
CoCreateInstance(&CLSID_ltmmPlay, NULL, CLSCTX_INPROC_SERVER, &IID_IltmmPlay, (void**) &pPlay);

C++ Source

IltmmPlay* pPlay;   
CoCreateInstance(&CLSID_ltmmPlay, NULL, CLSCTX_INPROC_SERVER, &IID_IltmmPlay, (void**) &pPlay);

2. Set the source file:

C Source

BSTR bstr;    
// create a string containing the source file path   
bstr = SysAllocString(L"C:\\MultipleAudio.mpg");    
// assign the source file path to the play object   
IltmmPlay_put_SourceFile(pPlay,  bstr);    
// free the string   
SysFreeString(bstr);

C++ Source

BSTR bstr;    
// create a string containing the source file path   
bstr = SysAllocString(L"C:\\MultipleAudio.mpg");   
// assign the source file path to the play object   
pPlay->put_SourceFile(bstr);    
// free the string   
SysFreeString(bstr);

3. The IAMStreamSelect is usually exposed by the file splitter (Demultiplexer), so you need to get a pointer to the splitter object:

C Source

IUnknown* pSplitter;   
IltmmPlay_GetSubObject (pPlay ,ltmmPlay_Object_Splitter, & pSplitter);

C++ Source

IUnknown* pSplitter;   
pPlay->GetSubObject (ltmmPlay_Object_Splitter, & pSplitter);

4. Query for the IAMStreamSelect interface:

C Source

IAMStreamSelect *pStreamSel = NULL;   
IUnknown_QueryInterface(pSplitter, &IID_IAMStreamSelect, (void**)& pStreamSel);   
IUnknown_Release(pSplitter);

C++ Source

IAMStreamSelect *pStreamSel = NULL;   
pSplitter->QueryInterface(&IID_IAMStreamSelect, (void**)&pStreamSel);   
pSplitter->Release();

5. Use the IAMStreamSelect interface to select one of the available audio streams in the file:

C Source

// retrieve the number of available streams in the file 
DWORD dwCount; 
int nIndex; 
BOOL bAudio = FALSE; 
BOOL bEnable = FALSE; 
AM_MEDIA_TYPE *pmt; 
DWORD dwFlags; 
LCID lcid; 
DWORD dwGroup; 
WCHAR *pszName; 
IUnknown *pObject; 
IUnknown *pUnk; 
IAMStreamSelect_Count(pStreamSel , &dwCount); 
for( nIndex = 0; nIndex<dwCount; nIndex++ ) 
{ 
// get information about the stream, and decide if this is an audio stream and you want to enable it: 
   IAMStreamSelect_Info(pStreamSel , nIndex, &pmt, &dwFlags, &lcid, &dwGroup, &pzsName, &pObject, &pUnk); 
    
   // based on your selection criterion 
   if( bAudio && bEnable ) 
      IAMStreamSelect_Enable(pStreamSel, nIndex, AMSTREAMSELECTENABLE_ENABLE); 
} 
IUnknown_Release(pStreamSel);

C++ Source

// retrieve the number of available streams in the file 
DWORD dwCount; 
int nIndex; 
BOOL bAudio = FALSE; 
BOOL bEnable = FALSE; 
AM_MEDIA_TYPE *pmt; 
DWORD dwFlags; 
LCID lcid; 
DWORD dwGroup; 
WCHAR *pszName; 
IUnknown *pObject; 
IUnknown *pUnk; 
 
pStreamSel->Count(&dwCount); 
for( nIndex = 0; nIndex<dwCount; nIndex++ ) 
{ 
// get information about the stream, and decide if this is an audio stream and you want to enable it: 
   pStreamSel->Info(nIndex, &pmt, &dwFlags, &lcid, &dwGroup, &pzsName, &pObject, &pUnk); 
    
   // based on your selection criterion 
   if( bAudio && bEnable ) 
      pStreamSel->Enable(nIndex,       AMSTREAMSELECTENABLE_ENABLE); 
} 
pStreamSel->Release();