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); }
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);}
~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。