作者：未知 来源：月光软件站 加入时间：2005-2-28　月光软件站

1. 预备知识 CMediaType[mtype.h/mtype.cpp]
   CMediaType从_AMMediaType继承，是一个在DirectShow中非常有用的Helper Class。它提供了一些常用的辅助函数来操作AMMediaType结构。另外，还提供了几个很常用的全局函数CreateMediaType、DeleteMediaType、CopyMediaType和FreeMediaType以及CreateAudioMediaType。
2. CBasePin类[amfilter.h/amfilter.cpp]
   
   • BasePin继承了接口IPin， IPin的接口定义如下
      IPin : public IUnknown
     {
         public:
         // 连接两个Pin，主动连接InputPin
         virtual HRESULT STDMETHODCALLTYPE Connect(
                 /* [in] */ IPin *pReceivePin,
                 /* [in] */ const AM_MEDIA_TYPE *pmt) = 0;
         // 连接两个Pin，被动连接
         virtual HRESULT STDMETHODCALLTYPE ReceiveConnection(
                 /* [in] */ IPin *pConnector,
                 /* [in] */ const AM_MEDIA_TYPE *pmt) = 0;
         // 断开连接，只能在Stop状态下断开
         virtual HRESULT STDMETHODCALLTYPE Disconnect( void) = 0;
         // 得到连接的Pin的接口，成功返回连接的Pin被调用AddRef
         virtual HRESULT STDMETHODCALLTYPE ConnectedTo(
                 /* [out] */ IPin **pPin) = 0;
         // 得到连接状态下的MediaType
         virtual HRESULT STDMETHODCALLTYPE ConnectionMediaType(
                 /* [out] */ AM_MEDIA_TYPE *pmt) = 0;
         // 得到Pin的信息，填充PIN_INFO结构
         virtual HRESULT STDMETHODCALLTYPE QueryPinInfo(
                 /* [out] */ PIN_INFO *pInfo) = 0;
         // 得到Pin的连接方向
         virtual HRESULT STDMETHODCALLTYPE QueryDirection(
                 /* [out] */ PIN_DIRECTION *pPinDir) = 0;
         // 得到ID － 其实是Pin中的name
         virtual HRESULT STDMETHODCALLTYPE QueryId(
                 /* [out] */ LPWSTR *Id) = 0;
         // Determines whether the pin accepts a specified media type.
         virtual HRESULT STDMETHODCALLTYPE QueryAccept(
                 /* [in] */ const AM_MEDIA_TYPE *pmt) = 0;
         // Enumerates the pin's preferred media types.
         virtual HRESULT STDMETHODCALLTYPE EnumMediaTypes(
                 /* [out] */ IEnumMediaTypes **ppEnum) = 0;
         // Retrieves the pins that are connected internally to this pin (within the filter).
         virtual HRESULT STDMETHODCALLTYPE QueryInternalConnections(
                 /* [out] */ IPin **apPin,
                 /* [out][in] */ ULONG *nPin) = 0;
         // Notifies the pin that no additional data is expected
         virtual HRESULT STDMETHODCALLTYPE EndOfStream( void) = 0;
         // Begins / End a flush operation.
         virtual HRESULT STDMETHODCALLTYPE BeginFlush( void) = 0;
         virtual HRESULT STDMETHODCALLTYPE EndFlush( void) = 0;
         // Notifies the pin that media samples received after this call are grouped as a segment.
         virtual HRESULT STDMETHODCALLTYPE NewSegment(
                 /* [in] */ REFERENCE_TIME tStart,
                 /* [in] */ REFERENCE_TIME tStop,
                 /* [in] */ double dRate) = 0;
         };
   • CBasePin同时继承了接口IQualityControl, IQualityControl的定义如下
     IQualityControl : public IUnknown
     {
     public:
         // Notifies the recipient that a quality change is requested.
         virtual HRESULT STDMETHODCALLTYPE Notify(
             /* [in] */ IBaseFilter *pSelf,
             /* [in] */ Quality q) = 0;
         virtual HRESULT STDMETHODCALLTYPE SetSink(
             /* [in] */ IQualityControl *piqc) = 0;
     };
   • CBasePin类的具体实现伪代码
     派生自 CUnknown, IPin, IQualityControl
     成员变量：
         WCHAR *         m_pName;          // This pin's name
         IPin            *m_Connected;               // Pin we have connected to
         PIN_DIRECTION   m_dir;                      // Direction of this pin
         CCritSec        *m_pLock;                   // Object we use for locking
         bool            m_bRunTimeError;            // Run time error generated
         bool            m_bCanReconnectWhenActive;  // OK to reconnect when active
         bool            m_bTryMyTypesFirst;         // When connecting enumerate
        CBaseFilter    *m_pFilter;                  // Filter we were created by
         IQualityControl *m_pQSink;                  // Target for Quality messages
         LONG            m_TypeVersion;              // Holds current type version
         CMediaType      m_mt;                       // Media type of connection
         CRefTime        m_tStart;                   // time from NewSegment call
         CRefTime        m_tStop;                    // time from NewSegment
         double          m_dRate;                    // rate from NewSegment
     其中m_bRunTimeError默认为FALSE，m_pQSink默认为NULL，m_TypeVersion默认为1，m_tStart为空，m_tStop为MAX_TIME，m_bCanReconnectWhenActive和m_bTryMyTypesFirst都为FALSE，m_dRate为1.0。
     构造函数部分：
     Constructor:
         CBasePin(
             TCHAR *pObjectName,         // Object description
             CBaseFilter *pFilter,       // Owning filter who knows about pins
             CCritSec *pLock,            // Object who implements the lock
             HRESULT *phr,               // General OLE return code
             LPCWSTR pName,              // Pin name for us
             PIN_DIRECTION dir);         // Either PINDIR_INPUT or PINDIR_OUTPUT
   • Pin之间的链接过程[详细Code讲解见陆其明《DirectShow开发指南》第二章的讲解]，通过调用IPin的Connect－>AgreeMediaType(CBasePin的Protected函数)->TryMediaTypes(CBasePin的Protected函数)->AttempConnect(CBasePin的Protected函数)。
     其中AttempConnect函数会首先调用CheckConnect(CBasePin的Virtual函数)，然后调用CheckMediaType(CBasePin的Virtual函数)，如果MediaType接受，则调用Receive Pin上的ReceiveConnection(IPin接口函数)函数，如果成功则调用CompleteConnection(CBasePin的virtual函数)。
   • CBasePin中的新增加virtual函数和解释以及虚拟代码:
     virtual LONG GetMediaTypeVersion();{return m_TypeVersion;}
     // switch the pin to active (paused or running) mode not an error to call this if already active,
     virtual HRESULT Active(void);{return NOERROR;}
     // switch the pin to inactive state - may already be inactive
     virtual HRESULT Inactive(void);{ return NOERROR; }
     // Notify of Run() from filter,
     virtual HRESULT Run(REFERENCE_TIME tStart);{ return NOERROR; }
     // check if the pin can support this specific proposed type and forma
     virtual HRESULT CheckMediaType(const CMediaType *) PURE; 必须Override
     // set the connection to use this format (previously agreed)
     virtual HRESULT SetMediaType(const CMediaType *);{ HRESULT hr = m_mt.Set(*pmt);}
     // check that the connection is ok before verifying it can be overridden eg to check what interfaces will be supported.
     virtual HRESULT CheckConnect(IPin *); {CBasePin中只检查了Pin的方向和当前方向是否一致}
     // Set and release resources required for a connection
     virtual HRESULT BreakConnect();{return NOERROR;}
     virtual HRESULT CompleteConnect(IPin *pReceivePin);
     // returns the preferred formats for a pin
     virtual HRESULT GetMediaType(int iPosition,CMediaType *pMediaType); 必须Override
   • CBasePin实现IPin的函数
     QueryAccept - 直接调用CheckMediaType，并将结果返回
     EnumMediaTypes - 通过辅助类CEnumMediaTypes实现MediaType的Enum.
     NewSegment – 只是简单设置参数后直接返回NOERROR
     Disconnect – 调用函数 DisconnectInternal
     Connect/ReceiveConnection – 见上面条目。
     其它的简单接口函数 ConnectionMediaType、QueryPinInfo、QueryDirection等。
   • CBasePin中未实现IPin/IQualityControl的函数
     直接设置为NOERROR的部分函数：
     EndOfStream
     直接设置为IMPL错误码的部分函数：
     QueryInternalConnections
     Notify[IQualityControl接口]
     完全没有实现的部分函数：
     BeginFlush
     EndFlush
3. CBaseOutputPin 类[amfilter.h/amfilter.cpp]
   • CBaseOutputPin具体实现伪代码
     派生自 CBasePin
     变量部分(均初始化为NULL)：
     IMemAllocator *m_pAllocator; // Memory allocator
     IMemInputPin *m_pInputPin;  // interface on the downstreaminput pin
   • 新增加的virtual函数：
     // negotiate the allocator and its buffer size/count and other properties
     // Calls DecideBufferSize to set properties
     virtual HRESULT DecideAllocator(IMemInputPin * pPin, IMemAllocator ** pAlloc);
     {
     // 调用 pPin->GetAllocatorRequirements. 得到Input Pin的Prop.
     // 调用 pPin->GetAllocator判断pPin是否以及存在Allocator，否则自己创建并初始化(InitAlloc)
     // 调用 DecideBufferSize 来得到需要的大小
     // 调用 pPin->NotifyAllocator让Input Pin得到更新的Allocator
     }
     // override this to set the buffer size and count. Return an error
     virtual HRESULT DecideBufferSize(
         IMemAllocator * pAlloc,
         ALLOCATOR_PROPERTIES * ppropInputRequest
     ) PURE;
     // returns an empty sample buffer from the allocator
     virtual HRESULT GetDeliveryBuffer(IMediaSample ** ppSample,
                                       REFERENCE_TIME * pStartTime,
                                       REFERENCE_TIME * pEndTime,
                                       DWORD dwFlags);
     {// 调用 m_pAllocator->GetBuffer… }
     // deliver a filled-in sample to the connected input pin
     // note - you need to release it after calling this. The receiving
     virtual HRESULT Deliver(IMediaSample *);{ m_pInputPin->Receive(pSample); }
     // override this to control the connection
     virtual HRESULT InitAllocator(IMemAllocator **ppAlloc);{ CreateMemoryAllocator(ppAlloc); }
     // called from elsewhere in our filter to pass EOS downstream to our connected input pin
     virtual HRESULT DeliverEndOfStream(void);{ m_Connected->EndOfStream(); }
     virtual HRESULT DeliverBeginFlush(void);{ m_Connected->BeginFlush(); }
     virtual HRESULT DeliverEndFlush(void);{ m_Connected->EndFlush(); }
     virtual HRESULT DeliverNewSegment(
                         REFERENCE_TIME tStart,
                         REFERENCE_TIME tStop,
                         double dRate);{ m_Connected->NewSegment(…);}
   • 继承的virtual函数或者IPin接口函数：
     // Complete connection
     virtual HRESULT CompleteConnect(IPin *pReceivePin); { DecideAllocator() }
     // Check connection
     HRESULT CheckConnect(IPin *pPin);
     {增加检查输入Pin是否支持IMemInputPin接口,m_pInputPin在这里赋值}
     // Break connection
     HRESULT BreakConnect();
     {
     // 调用m_pAllocator->Decommit()后释放m_pAllocator并置为空,
     // 释放m_pInputPin并置为空
     }
     HRESULT Active(void);{ m_pAllocator->Commit(); }
     HRESULT Inactive(void); { m_pAllocator->Decommit();}
     // 以下三个函数直接返回E_UNEXPECTED
     STDMETHODIMP EndOfStream(void);
     STDMETHODIMP BeginFlush(void);
     STDMETHODIMP EndFlush(void);
4. IMemInput接口函数：
   // Retrieves the memory allocator proposed by this pin.
   virtual HRESULT STDMETHODCALLTYPE GetAllocator(
       /* [out] */ IMemAllocator **ppAllocator) = 0;
   // Specifies an allocator for the connection.
   virtual HRESULT STDMETHODCALLTYPE NotifyAllocator(
       /* [in] */ IMemAllocator *pAllocator,
       /* [in] */ BOOL bReadOnly) = 0;
   // Retrieves allocator properties that are requested by the input pin.
   virtual HRESULT STDMETHODCALLTYPE GetAllocatorRequirements(
       /* [out] */ ALLOCATOR_PROPERTIES *pProps) = 0;
   // Receives the next media sample in the stream.
   virtual HRESULT STDMETHODCALLTYPE Receive(
       /* [in] */ IMediaSample *pSample) = 0;
   // Receives multiple samples in the stream.
   virtual HRESULT STDMETHODCALLTYPE ReceiveMultiple(
       /* [size_is][in] */ IMediaSample **pSamples,
       /* [in] */ long nSamples,
       /* [out] */ long *nSamplesProcessed) = 0;
   // Determines whether calls to the Recive method might block.
   virtual HRESULT STDMETHODCALLTYPE ReceiveCanBlock( void) = 0;
5. CBaseInputPin类[amfilter.h/amfilter.cpp]
   • CBaseInputPin具体实现伪代码：
     派生自 CBasePin, IMemInputPin
     变量部分：
     IMemAllocator *m_pAllocator;    // Default memory allocator
     // Allocator is read only or not
     BYTE m_bReadOnly;
     // in flushing state (between BeginFlush and EndFlush)
     // if TRUE, all Receives are returned with S_FALSE
     BYTE m_bFlushing;
     // Sample properties - initalized in Receive
     AM_SAMPLE2_PROPERTIES m_SampleProps;
     INonDelegationUnknown的接口函数：
     // 重写该函数是为了支持IMemInputPin接口。
     STDMETHODIMP NonDelegatingQueryInterface(REFIID riid, void **ppv);
     具体实现函数：
     HRESULT PassNotify(Quality& q);
     {
     // 如果m_pQSink不为空，直接调用m_pQSink->Notify(…)
     // 否则查询Connect Pin上的IQualityControl借口，对其调用Notify(…)
     }
   • 新增的virtual函数
     //  Override this for checking whether it's OK to process samples
     //  Also call this from EndOfStream.
     virtual HRESULT CheckStreaming();
     {分别判断IsStopped、m_bFlushing和m_bRunTimeError }
   • IMemInputPin接口函数：
     // return the allocator interface that this input pin
     // would like the output pin to use
     STDMETHODIMP GetAllocator(IMemAllocator ** ppAllocator);
     {
     // 如果m_pAllocator为空，则CreateMemoryAllocator。
     // 调用m_pAllocator->AddRef，返回m_pAllocator
     }
     // tell the input pin which allocator the output pin is actually going to use.
     STDMETHODIMP NotifyAllocator(
                     IMemAllocator * pAllocator,
                     BOOL bReadOnly);
     {
     // 释放当前m_pAllocator，设置m_pAllocator = pAllocator
     // 调用m_pAllocator->AddRef
     }
     // do something with this media sample
     STDMETHODIMP Receive(IMediaSample *pSample);
     {
     // 首先调用CheckStreaming
     // 得出pSample的属性，即填充成员m_SampleProps
     // 如果Sample属性未发生变化(!(m_SampleProps.dwSampleFlags & AM_SAMPLE_TYPECHANGED))
     // 则直接返回NOERROR，否则调用CheckMediaType检查是否接受新的MediaType，如果接受
     // 返回NOERROR，否则调用EndOfStream，设置RuntimeError，并通知Filter
     // m_pFilter->NotifyEvent(EC_ERRORABORT,VFW_E_TYPE_NOT_ACCEPTED,0);
     }
     // do something with these media samples
     STDMETHODIMP ReceiveMultiple (
         IMediaSample **pSamples,
         long nSamples,
         long *nSamplesProcessed);
     {
     // 对每个Sample分别调用Receive函数。
     }
     // See if Receive() blocks
     STDMETHODIMP ReceiveCanBlock();
     {
     // 如果当前Filter上没有Output Pin，则返回S_OK
     // 否则遍历当前Filter上每个Output Pin，得出它们的Connected Input Pin，判断这些
     // Connected Input Pin是否支持Block，只要有一个支持，则为S_OK
     // 以上条件全不满足时，返回S_FALSE
     }
     // default implementation returns E_NOTIMPL. Override if you have
     // specific alignment or prefix needs, but could use an upstream allocator
     STDMETHODIMP GetAllocatorRequirements(ALLOCATOR_PROPERTIES*pProps);{E_IMPL}
   • 继承的virtual函数实现
     STDMETHODIMP BeginFlush(void);
     {仅仅设置m_bFlushing为TRUE.}
     STDMETHODIMP EndFlush(void);
     {仅仅设置m_bFlushing为FALSE，同时清除m_bRuntimeError。}
     HRESULT BreakConnect();
     {
     // 如果m_pAllocator非空，调用m_pAllocator->Decommit()
     // 释放m_pAllocator->Release并置为空。
     }
     virtual HRESULT Inactive(void);
     {
     // 清理m_bRunTimeError和m_bFlushing，返回m_pAllocator->Decommit().
     }
     STDMETHODIMP Notify(IBaseFilter * pSender, Quality q);
     {这是IQualityControl的接口函数，CBaseInputPin只是简单报错DbgBreak说明未实现}
6. 学习三将侧重于Filter的代码分析

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