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Using Multiple Bit Rate Mutual Exclusion

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[The feature associated with this page, Windows Media Format 11 SDK, is a legacy feature. It has been superseded by Source Reader and Sink Writer. Source Reader and Sink Writer have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use Source Reader and Sink Writer instead of Windows Media Format 11 SDK, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

Multiple bit rate (MBR) mutual exclusion is useful when you want to encode content for a variety of playback scenarios. An MBR video output consists of a single input encoded multiple times, each with different bit-rate settings. When a file with MBR encoding is read, the reader will determine which stream to use based on the available bandwidth.

The Windows Media Format SDK supports MBR encoding for both video and audio streams. In addition, you can create a special type of MBR encoding called multiple-video-size MBR encoding. Multiple-video-size MBR video functions identically to normal MBR video except that you can specify different image sizes for the video streams in the mutual exclusion.

The following example demonstrates how to set up a profile for MBR video with multiple video sizes. It creates a new profile with three video streams of varying bit rates and sizes, and includes them in a mutual exclusion object.

IWMProfileManager*  pProfileMgr = NULL;
IWMProfile*         pProfile    = NULL;
IWMMutualExclusion* pMutex      = NULL;
IWMStreamConfig*    pStream     = NULL;
IWMMediaProps*      pMediaProps = NULL;

WM_MEDIA_TYPE*      pMediaType  = NULL;
DWORD               cbMediaType = 0;

HRESULT hr = S_OK;

// Initialize COM.
hr = CoInitialize(NULL);

// Create a profile manager object.
hr = WMCreateProfileManager(&pProfileMgr);

// Create an empty profile.
hr = pProfileMgr->CreateEmptyProfile(WMT_VER_9_0, &pProfile);

// Give the new profile a name and description.
hr = pProfile->SetName(L"MBR_Video_3_Stream_test");
hr = pProfile->SetDescription(L"Only for use with example code.");

// Create the first stream.
hr = pProfile->CreateNewStream(WMMEDIATYPE_Video, &pStream);

// Get the media properties interface for the new stream.
hr = pStream->QueryInterface(IID_IWMMediaProps, (void**)&pMediaProps);

// Get the media-type structure.
// First, get the size of the media-type structure.
hr = pMediaProps->GetMediaType(NULL, &cbMediaType);

// Allocate memory for the structure based on the retrieved size.
pMediaType = (WM_MEDIA_TYPE*) new BYTE[cbMediaType];

// Retrieve the media-type structure.
hr = pMediaProps->GetMediaType(pMediaType, &cbMediaType);

// Change the video size to 640 x 480.
pMediaType->pbFormat->bmiHeader.biWidth  = 640;
pMediaType->pbFormat->bmiHeader.biHeight = 480;

// Replace the WM_MEDIA_TYPE in the profile with the one just changed.
hr = pMediaProps->SetMediaType(pMediaType);

// Release the media properties interface and delete the structure.
pMediaProps->Release();
pMediaProps = NULL;
delete[] pMediaType;
pMediaType = NULL;

// Set the bit rate to 200.
hr = pStream->SetBitrate(200000);

// Set the stream number.
hr = pStream->SetStreamNumber(1);

// Include the new stream in the profile.
hr = pProfile->AddStream(pStream);

// Release the stream configuration interface.
pStream->Release();
pStream = NULL;

// For the remaining two streams, leave the video at its default size of
// 320 x 240 <entity type="ndash"/>- just change the bit rates.

// Repeat for a 100K stream.
hr = pProfile->CreateNewStream(WMMEDIATYPE_Video, &pStream);
hr = pStream->SetBitrate(100000);
hr = pStream->SetStreamNumber(2);
hr = pProfile->AddStream(pStream);
pStream->Release();
pStream = NULL;

// Repeat for a 56K stream.
hr = pProfile->CreateNewStream(WMMEDIATYPE_Video, &pStream);
hr = pStream->SetBitrate(56000);
hr = pStream->SetStreamNumber(3);
hr = pProfile->AddStream(pStream);
pStream->Release();
pStream = NULL;

// Now that we have three streams, create a mutual exclusion object.
hr = pProfile->CreateNewMutualExclusion(&pMutex);

// Add the three streams to the mutual exclusion.
hr = pMutex->AddStream(1);
hr = pMutex->AddStream(2);
hr = pMutex->AddStream(3);

// Configure the mutual exclusion for MBR video.
hr = pMutex->SetType(CLSID_WMMUTEX_Bitrate);

// Add the mutual exclusion to the profile.
hr = pProfile->AddMutualExclusion(pMutex);

// Release the mutual exclusion object.
pMutex->Release();
pMutex = NULL;

// TODO: Save the profile to a string, and save the string to a file.
// For more information, see To Save a Custom Profile.

// Release remaining interfaces.
pProfile->Release();
pProfile = NULL;

pProfileMgr->Release();
pProfileMgr = NULL;

IWMMediaProps Interface

IWMMutualExclusion Interface

IWMProfile Interface

IWMStreamConfig Interface

Using Mutual Exclusion

WM_MEDIA_TYPE