Topic in microsoft.public.windowsmedia.sdk
how to use IWMWriterSink::OnDataUnit
Q:
I want to use IWMWriterSink::OnDataUnit() to get the
compressed sample. I modify the WMVNetWrite sample
application for test app, add the following:
IWMWriterNetSink->QurryInterfaceIID_IWMWriterSink,
m_pWriterSink)
m_pWriterSink->AllocateDataUnit();
m_pWriterSink->OnDataUnit();
then use the INSSBuffer::GetBufferAndLength(),but the
buffer content is null! I don't know how to use the
interface: If the OnDataUnit is a callback function, it
should be inherented by a class , otherwise , query
interface to get it, but where and how to call the
OnDataUnit function.
I am waiting for your help
regards
billy
A:
If you want to override OnDataUnit() method of a network sinker. You need to
do these steps:
1. Define a new class that inherits from IWMClientConnections2,
IWMRegisterCallback, IWMWriterNetworkSinkobject, and IWMAddressAccess2
interfaces.
For example:
class CMyWMNetSink : public IWMWriterNetworkSink,
public IWMClientConnections2,
public IWMRegisterCallback,
public IWMAddressAccess2
2. Besides declare the constructor and the destructor of this class,
you also need to declare all methods of the inherited interfaces.
For example:
virtual HRESULT STDMETHODCALLTYPE OnDataUnit(
/* [in] */ INSSBuffer __RPC_FAR *pDataUnit);
3. Implement the constructor of this class
a) Set the reference count to 1
b) Create an internal IWMWriterNetworkSink object m_pNetworkSink by
using WMCreateWriterNetworkSink() function.
4. Implement IUnknow interfaces.
a) Implement AddRef() and Release() method just like you implement
other COM interfaces.
b) Imlplement QueryInterface() method. Return "this" pointer when
querying the supported interfaces, such as IID_IWMWriterNetworkSink,
IID_IWMWriterSink and etc.
5. Implement all other interfaces this class supports. Pass the calls
to the internal IWMWriterNetworkSinker object. Add your own code before or
after the calls.
For example:
HRESULT STDMETHODCALLTYPE CMyWMNetSink::OnDataUnit(
/* [in] */ INSSBuffer __RPC_FAR *pDataUnit)
{
////////////////////////////////////////////
// You can add you code here
////////////////////////////////////////////
IWMWriterSink * pWriterSink = NULL;
HRESULT hr = S_OK;
hr = m_pNetworkSink->QueryInterface( IID_IWMWriterSink, (void
**)&pWriterSink ); if ( FAILED( hr ) ) {return hr;}
hr = pWriterSink->OnDataUnit( pDataUnit ); if ( FAILED( hr ) ) { pWriterSink->Release(); return hr;}
pWriterSink->Release();
/////////////////////////////////////////////////
// You can also add you code here
/////////////////////////////////////////////////
return hr;
}
6. Create an instance of this class in your program. Get the
IWMWriterNetworkSink interface from this instance.
For example:
IWMWriterNetworkSink * pNetworkSink = NULL;
CMyWMNetSink * pMySink = new CMyWMNetSink();
if ( pMySink == NULL ) { return E_OUTOFMEMORY; }
hr = pMySink->QueryInterface( IID_IWMWriterNetworkSink, (void
**)&pNetworkSink ); if ( FAILED( hr ) ) { return hr; }
7. Then you can use this IWMWriterNetworkSink interface in your
program.
--
Thanks!
Gangjiang Li
Microsoft Corp.
Windows Media Format SDK
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