关于CSource和CSourceStream .

CSourceStream类，是CSource类的OutputPin[source.h/source.cpp]

派生自CAMThread和CBaseOutputPin
l         成员变量：

CSource *m_pFilter;    // The parent of this stream//在构造的时候作为输入参数

l         新增加的virtual函数：
// Override this to provide the worker thread a means of processing a buffer
virtual HRESULT FillBuffer(IMediaSample *pSamp) PURE;
// Called as the thread is created/destroyed - use to perform
// jobs such as start/stop streaming mode
// If OnThreadCreate returns an error the thread will exit.
virtual HRESULT OnThreadCreate(void) {return NOERROR;};
virtual HRESULT OnThreadDestroy(void) {return NOERROR;};
virtual HRESULT OnThreadStartPlay(void) {return NOERROR;};

virtual HRESULT DoBufferProcessingLoop(void);    // the loop executed whilst running
{
     Command com;
     OnThreadStartPlay();//你可以重载这个函数，可以在play之前作一些操作
     do
     {
          while (!CheckRequest(&com))//

//Determines if a command is waiting for the thread.

//TRUE if the pCom parameter contains a command; otherwise, returns FALSE

         {
               IMediaSample *pSample;
               HRESULT hr = GetDeliveryBuffer(&pSample,NULL,NULL,0);
              //这个函数是baseoutputpin的成员函数，返回一块空白的内存区域，需要去填充数据的
              //实际上是调用IMemAllocator::GetBuffer函数来实现的           
               if (FAILED(hr)) { Sleep(1); continue;}
               // Virtual function user will override.
              //得到数据之后，就填充数据
               hr = FillBuffer(pSample);
               if (hr == S_OK)
               { hr = Deliver(pSample); pSample->Release();if(hr != S_OK) return S_OK;}
               //上面的这个函数调用的是This method calls the IMemInputPin::Receive method on the input pin.  //Receive can block if the IMemInputPin::ReceiveCanBlock method returns S_OK.
//这样你的接收的filter就阻塞去接收数据
               else if (hr == S_FALSE)
               { pSample->Release();DeliverEndOfStream();return S_OK;}
               else
               {
                    pSample->Release();DeliverEndOfStream();
                    m_pFilter->NotifyEvent(EC_ERRORABORT, hr, 0);
                    return hr;
               }
         }
         if (com == CMD_RUN || com == CMD_PAUSE) { Reply(NOERROR); }
         else if (com != CMD_STOP) { Reply((DWORD) E_UNEXPECTED);}
    }
    while (com != CMD_STOP);
    return S_FALSE;
}
上面的reply是下面的一个CAMThread的函数
上面BOOL    CheckRequest(Command *pCom) { return CAMThread::CheckRequest( (DWORD *) pCom); }
        继承的CBasePin的virtual函数：
HRESULT Active(void);    // Starts up the worker thread
{
     CAutoLock lock(m_pFilter->pStateLock());
     if (m_pFilter->IsActive()) {return S_FALSE;}
     if (!IsConnected()) {return NOERROR;}
     hr = CBaseOutputPin::Active();
     if (FAILED(hr)) {return hr;}
     ASSERT(!ThreadExists());
     // start the thread
     if (!Create()) {return E_FAIL;}
     // Tell thread to initialize. If OnThreadCreate Fails, so does this.
     hr = Init();
     if (FAILED(hr)) return hr;
     return Pause();
}
HRESULT Inactive(void); // Exits the worker thread.
{
     CAutoLock lock(m_pFilter->pStateLock());
     if (!IsConnected()) {return NOERROR;}
     // !!! need to do this before trying to stop the thread, because
     // we may be stuck waiting for our own allocator!!!
     hr = CBaseOutputPin::Inactive(); // call this first to Decommit the allocator
     if (FAILED(hr)) {return hr;}
     if (ThreadExists())
     {
          hr = Stop();if (FAILED(hr)) {return hr;}
          hr = Exit();if (FAILED(hr)) {return hr;}
          Close(); // Wait for the thread to exit, then tidy up.
     }
     return NOERROR;
}
virtual HRESULT CheckMediaType(const CMediaType *pMediaType);
{
// 默认只支持一种格式，即只调用新增加的GetMediaType函数得到MediaType，
// 与输入的Type进行比较
}
virtual HRESULT GetMediaType(int iPosition, CMediaType *pMediaType); // List pos. 0-n
{
// 判断iPosition必须为0，返回新增加的GetMediaType函数
}

l         操作函数：
HRESULT Init(void) { return CallWorker(CMD_INIT); }
HRESULT Exit(void) { return CallWorker(CMD_EXIT); }
HRESULT Run(void) { return CallWorker(CMD_RUN); }
HRESULT Pause(void) { return CallWorker(CMD_PAUSE); }
HRESULT Stop(void) { return CallWorker(CMD_STOP); }

我们通过上面的代码发现，CAMThread和CBaseOutputPin关联很紧密，下面我们来看看CAMThread是一个什么样的类

l         CAMThread的virtual函数
// override these if you want to add thread commands
// Return codes > 0 indicate an error occured
virtual DWORD ThreadProc(void);        // the thread function
{
     // 整个函数实现了一个同步的通讯Thread。
     Command com;
     do { com = GetRequest();if (com != CMD_INIT) { Reply((DWORD) E_UNEXPECTED);} }
     while (com != CMD_INIT);
     hr = OnThreadCreate(); // perform set up tasks
     if (FAILED(hr))
     {
          OnThreadDestroy();
          Reply(hr);   // send failed return code from OnThreadCreate
          return 1;
     }
     Reply(NOERROR);
     Command cmd;
    do
    {
         cmd = GetRequest();
         switch (cmd) {
         case CMD_EXIT: Reply(NOERROR); break;
         case CMD_RUN:
         case CMD_PAUSE:Reply(NOERROR); DoBufferProcessingLoop();break;
         case CMD_STOP: Reply(NOERROR); break;
         default: Reply((DWORD) E_NOTIMPL); break;}
     }
     while (cmd != CMD_EXIT);
     hr = OnThreadDestroy(); // tidy up.
     if (FAILED(hr)) { return 1;}
     return 0;
}

l         Constructor：
// increments the number of pins present on the filter
CSourceStream(TCHAR *pObjectName, HRESULT *phr, CSource *ps, LPCWSTR pPinName)
: CBaseOutputPin(pObjectName, ps, ps->pStateLock(), phr, pPinName),
m_pFilter(ps) {*phr = m_pFilter->AddPin(this);}

l         Deconstructor：
~CSourceStream(void) {m_pFilter->RemovePin(this);}

这个类要实现就是这个函数了，注意Reply函数经常调用，因为
CAMThread::Reply(DWORD dw)
{
    m_dwReturnVal = dw;
   
    // The request is now complete so CheckRequest should fail from
    // now on
    //
    // This event should be reset BEFORE we signal the client or
    // the client may Set it before we reset it and we'll then
    // reset it (!)
   
    m_EventSend.Reset();
   
    // Tell the client we're finished
   
    m_EventComplete.Set();
}
有兴趣的可以继续往下研究，我觉得个人开发需求，到这就够了。
后面，我们结合我们的代码，看看CSourceStream在实际的应用是怎么使用的。