Filter组件开发中的SDK基类分析 分类： DirectX 2014-10-09 15:50 477人阅读 评论(0) 收藏

DirectShow SDK提供了一套开发Filter的基类源代码。基于这些基类开发Filter将大大简化开发过程。

1、CBaseObject

大部分SDK类都从CBaseObject类（参见combase.h）中继承而来的。

class CBaseObject
{

private:

    // Disable the copy constructor and assignment by default so you will get
    //   compiler errors instead of unexpected behaviour if you pass objects
    //   by value or assign objects.
    CBaseObject(const CBaseObject& objectSrc);          // no implementation
    void operator=(const CBaseObject& objectSrc);       // no implementation

private:
    static LONG m_cObjects;     /* Total number of objects active */

protected:
#ifdef DEBUG
    DWORD m_dwCookie;           /* Cookie identifying this object */
#endif


public:

    /* These increment and decrement the number of active objects */

    CBaseObject(const TCHAR *pName);
#ifdef UNICODE
    CBaseObject(const char *pName);
#endif
    ~CBaseObject();

    /* Call this to find if there are any CUnknown derived objects active */

    static LONG ObjectsActive() {
        return m_cObjects;
    };
};

2、 CUnknown

作为COM组件（参见combase.cpp文件），最基本的当然是IUnknown接口的实现。SDK提供了CUnknown类，SDK实现了COM接口类都是直接或间接从这个类继承来的。

class AM_NOVTABLE CUnknown : public INonDelegatingUnknown,
                 public CBaseObject
{
private:
    const LPUNKNOWN m_pUnknown; /* Owner of this object */

protected:                      /* So we can override NonDelegatingRelease() */
    volatile LONG m_cRef;       /* Number of reference counts */

public:

    CUnknown(const TCHAR *pName, LPUNKNOWN pUnk);
    virtual ~CUnknown() {};

    // This is redundant, just use the other constructor
    //   as we never touch the HRESULT in this anyway
    CUnknown(TCHAR *pName, LPUNKNOWN pUnk,HRESULT *phr);
#ifdef UNICODE
    CUnknown(const char *pName, LPUNKNOWN pUnk);
    CUnknown(char *pName, LPUNKNOWN pUnk,HRESULT *phr);
#endif

    /* Return the owner of this object */

    LPUNKNOWN GetOwner() const {
        return m_pUnknown;
    };

    /* Called from the class factory to create a new instance, it is
       pure virtual so it must be overriden in your derived class */

    /* static CUnknown *CreateInstance(LPUNKNOWN, HRESULT *) */

    /* Non delegating unknown implementation */

    STDMETHODIMP NonDelegatingQueryInterface(REFIID, void **);
    STDMETHODIMP_(ULONG) NonDelegatingAddRef();
    STDMETHODIMP_(ULONG) NonDelegatingRelease();
};

CUnknown类从CBaseObject中继承而来，另外CUnknown类还实现了INonDelegatingUnknown接口，用于支持引用计数、接口查询、COM组件“聚合”等。

CUnknown类的使用方法如下：

（1） 从CUnknown派生一个子类，并在子类的public区加入DECLARE_IUNKNOWN宏；

（2） 重写NonDelegatingQueryInterface函数，用以支持IUnknown外的其他接口；

（3） 在子类的构造函数中调用CUnknown的构造函数。

eg:

class CSeekingPassThru : public ISeekingPassThru, public CUnknown
{
public:
    static CUnknown *CreateInstance(LPUNKNOWN pUnk, HRESULT *phr);
    CSeekingPassThru(TCHAR *pName, LPUNKNOWN pUnk, HRESULT *phr);
    ~CSeekingPassThru();

    DECLARE_IUNKNOWN;
    STDMETHODIMP NonDelegatingQueryInterface(REFIID riid, void ** ppv);

    STDMETHODIMP Init(BOOL bSupportRendering, IPin *pPin);

private:
    CPosPassThru              *m_pPosPassThru;
};

 

CSeekingPassThru::CSeekingPassThru( TCHAR *pName, LPUNKNOWN pUnk, HRESULT *phr )
                            : CUnknown(pName, pUnk, phr),
                            m_pPosPassThru(NULL)
{
}

3、 CBaseFilter

最基本的Filter由CBaseFilter 类（参见amfilter.cpp）实现。

作为Filter的基本特征，CBaseFilter实现了IBaseFilter接口（IbaseFilter从IMediaFilter继承而来）。

同时CBaseFilter还实现了Filter框架（描述了各个Pin组件的情况）。

class AM_NOVTABLE CBaseFilter : public CUnknown,        // Handles an IUnknown
                    public IBaseFilter,     // The Filter Interface
                    public IAMovieSetup     // For un/registration
{

friend class CBasePin;

protected:
    FILTER_STATE    m_State;            // current state: running, paused
    IReferenceClock *m_pClock;          // this graph's ref clock
    CRefTime        m_tStart;           // offset from stream time to reference time
    CLSID       m_clsid;            // This filters clsid
                                        // used for serialization
    CCritSec        *m_pLock;           // Object we use for locking

    WCHAR           *m_pName;           // Full filter name
    IFilterGraph    *m_pGraph;          // Graph we belong to
    IMediaEventSink *m_pSink;           // Called with notify events
    LONG            m_PinVersion;       // Current pin version

public:

    CBaseFilter(
        const TCHAR *pName,     // Object description
        LPUNKNOWN pUnk,         // IUnknown of delegating object
        CCritSec  *pLock,       // Object who maintains lock
    REFCLSID   clsid);      // The clsid to be used to serialize this filter

    CBaseFilter(
        TCHAR     *pName,       // Object description
        LPUNKNOWN pUnk,         // IUnknown of delegating object
        CCritSec  *pLock,       // Object who maintains lock
    REFCLSID   clsid,       // The clsid to be used to serialize this filter
        HRESULT   *phr);        // General OLE return code
#ifdef UNICODE
    CBaseFilter(
        const CHAR *pName,     // Object description
        LPUNKNOWN pUnk,         // IUnknown of delegating object
        CCritSec  *pLock,       // Object who maintains lock
    REFCLSID   clsid);      // The clsid to be used to serialize this filter

    CBaseFilter(
        CHAR     *pName,       // Object description
        LPUNKNOWN pUnk,         // IUnknown of delegating object
        CCritSec  *pLock,       // Object who maintains lock
    REFCLSID   clsid,       // The clsid to be used to serialize this filter
        HRESULT   *phr);        // General OLE return code
#endif
    ~CBaseFilter();

    DECLARE_IUNKNOWN

    // override this to say what interfaces we support where
    STDMETHODIMP NonDelegatingQueryInterface(REFIID riid, void ** ppv);
#ifdef DEBUG
    STDMETHODIMP_(ULONG) NonDelegatingRelease();
#endif

    //
    // --- IPersist method ---
    //

    STDMETHODIMP GetClassID(CLSID *pClsID);

    // --- IMediaFilter methods ---

    STDMETHODIMP GetState(DWORD dwMSecs, FILTER_STATE *State);

    STDMETHODIMP SetSyncSource(IReferenceClock *pClock);

    STDMETHODIMP GetSyncSource(IReferenceClock **pClock);


    // override Stop and Pause so we can activate the pins.
    // Note that Run will call Pause first if activation needed.
    // Override these if you want to activate your filter rather than
    // your pins.
    STDMETHODIMP Stop();
    STDMETHODIMP Pause();

    // the start parameter is the difference to be added to the
    // sample's stream time to get the reference time for
    // its presentation
    STDMETHODIMP Run(REFERENCE_TIME tStart);

    // --- helper methods ---

    // return the current stream time - ie find out what
    // stream time should be appearing now
    virtual HRESULT StreamTime(CRefTime& rtStream);

    // Is the filter currently active?
    BOOL IsActive() {
        CAutoLock cObjectLock(m_pLock);
        return ((m_State == State_Paused) || (m_State == State_Running));
    };

    // Is this filter stopped (without locking)
    BOOL IsStopped() {
        return (m_State == State_Stopped);
    };

    //
    // --- IBaseFilter methods ---
    //

    // pin enumerator
    STDMETHODIMP EnumPins(
                    IEnumPins ** ppEnum);


    // default behaviour of FindPin assumes pin ids are their names
    STDMETHODIMP FindPin(
        LPCWSTR Id,
        IPin ** ppPin
    );

    STDMETHODIMP QueryFilterInfo(
                    FILTER_INFO * pInfo);

    STDMETHODIMP JoinFilterGraph(
                    IFilterGraph * pGraph,
                    LPCWSTR pName);

    // return a Vendor information string. Optional - may return E_NOTIMPL.
    // memory returned should be freed using CoTaskMemFree
    // default implementation returns E_NOTIMPL
    STDMETHODIMP QueryVendorInfo(
                    LPWSTR* pVendorInfo
            );

    // --- helper methods ---

    // send an event notification to the filter graph if we know about it.
    // returns S_OK if delivered, S_FALSE if the filter graph does not sink
    // events, or an error otherwise.
    HRESULT NotifyEvent(
        long EventCode,
        LONG_PTR EventParam1,
        LONG_PTR EventParam2);

    // return the filter graph we belong to
    IFilterGraph *GetFilterGraph() {
        return m_pGraph;
    }

    // Request reconnect
    // pPin is the pin to reconnect
    // pmt is the type to reconnect with - can be NULL
    // Calls ReconnectEx on the filter graph
    HRESULT ReconnectPin(IPin *pPin, AM_MEDIA_TYPE const *pmt);

    // find out the current pin version (used by enumerators)
    virtual LONG GetPinVersion();
    void IncrementPinVersion();

    // you need to supply these to access the pins from the enumerator
    // and for default Stop and Pause/Run activation.
    virtual int GetPinCount() PURE;
    virtual CBasePin *GetPin(int n) PURE;

    // --- IAMovieSetup methods ---

    STDMETHODIMP Register();    // ask filter to register itself
    STDMETHODIMP Unregister();  // and unregister itself

    // --- setup helper methods ---
    // (override to return filters setup data)

    virtual LPAMOVIESETUP_FILTER GetSetupData(){ return NULL; }

};

CBaseFilter类的使用方法如下：

（1） 声明一个新类是从CBaseFilter中继承而来；

（2） 在新类中定义Filter上的Pin的实例（Pin从CBasePin类继承而来）；

（3） 实现纯虚函数CBaseFilter::GetPin，用于返回Filter上各个Pin的对象指针；

（4） 实现纯虚函数CBaseFilter::GetPinCount，用于返回Filter上Pin 的数量；

（5） 考虑如何处理从输入Pin进来的Sample数据。

eg:

//
// The filter object itself. Supports IBaseFilter through
// CBaseFilter and also IFileSourceFilter directly in this object
// CAsyncReader类实现了一个Filter，它从CBaseFilter派生，实现了仅含一个输出
// Pin(CAsyncOutputPin类的实例)的Source filter框架。
class CAsyncReader : public CBaseFilter
{

protected:
    // filter-wide lock
    CCritSec m_csFilter;

    // all i/o done here
    CAsyncIo m_Io;

    // (2)在新类中定义Filter上的Pin的实例（Pin从CBasePin类继承而来）；
    // our output pin
    CAsyncOutputPin m_OutputPin;

    // Type we think our data is
    CMediaType m_mt;

public:

    // construction / destruction

    CAsyncReader(
        TCHAR *pName,
        LPUNKNOWN pUnk,
        CAsyncStream *pStream, // 它是Filter获取数据的源
        HRESULT *phr);

    ~CAsyncReader();


    //（3） 实现纯虚函数CBaseFilter::GetPin，用于返回Filter上各个Pin的对象指针；
    //（4） 实现纯虚函数CBaseFilter::GetPinCount，用于返回Filter上Pin 的数量；
    int GetPinCount();
    CBasePin *GetPin(int n);

    // --- Access our media type
    const CMediaType *LoadType() const
    {
        return &m_mt;
    }

    virtual HRESULT Connect(
        IPin * pReceivePin,
        const AM_MEDIA_TYPE *pmt   // optional media type
    )
    {
        return m_OutputPin.CBasePin::Connect(pReceivePin, pmt);
    }
};

还有SDK类的CSource、CBaseRenderer、 CTracsformFilter都是从CBaseFilter继承来的，实现开发Filter时，

使用这些子类作为Filter类。

4、CBasePin

Filter  上最基本的Pin由CBasePin类（参见 amfilter.h）实现。

作为Pin的基本特征，CBasePin实现了IPin接口。CBasePin设计了Pin 的整个连接过程。

另外，这个类还实现了IQualityControl接口，该接口用于质量控制。

class  AM_NOVTABLE CBasePin : public CUnknown, public IPin, public IQualityControl
{

protected:

    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
                                                // this pin's types first
    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

#ifdef DEBUG
    LONG            m_cRef;                     // Ref count tracing
#endif

    // displays pin connection information

#ifdef DEBUG
    void DisplayPinInfo(IPin *pReceivePin);
    void DisplayTypeInfo(IPin *pPin, const CMediaType *pmt);
#else
    void DisplayPinInfo(IPin *pReceivePin) {};
    void DisplayTypeInfo(IPin *pPin, const CMediaType *pmt) {};
#endif

    // used to agree a media type for a pin connection

    // given a specific media type, attempt a connection (includes
    // checking that the type is acceptable to this pin)
    HRESULT
    AttemptConnection(
        IPin* pReceivePin,      // connect to this pin
        const CMediaType* pmt   // using this type
    );

    // try all the media types in this enumerator - for each that
    // we accept, try to connect using ReceiveConnection.
    HRESULT TryMediaTypes(
                        IPin *pReceivePin,      // connect to this pin
                        const CMediaType *pmt,        // proposed type from Connect
                        IEnumMediaTypes *pEnum);    // try this enumerator

    // establish a connection with a suitable mediatype. Needs to
    // propose a media type if the pmt pointer is null or partially
    // specified - use TryMediaTypes on both our and then the other pin's
    // enumerator until we find one that works.
    HRESULT AgreeMediaType(
                        IPin *pReceivePin,      // connect to this pin
                        const CMediaType *pmt);       // proposed type from Connect

public:

    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
#ifdef UNICODE
    CBasePin(
        CHAR *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
#endif
    virtual ~CBasePin();

    DECLARE_IUNKNOWN

    STDMETHODIMP NonDelegatingQueryInterface(REFIID riid, void ** ppv);
    STDMETHODIMP_(ULONG) NonDelegatingRelease();
    STDMETHODIMP_(ULONG) NonDelegatingAddRef();

    // --- IPin methods ---

    // take lead role in establishing a connection. Media type pointer
    // may be null, or may point to partially-specified mediatype
    // (subtype or format type may be GUID_NULL).
    STDMETHODIMP Connect(
        IPin * pReceivePin,
        const AM_MEDIA_TYPE *pmt   // optional media type
    );

    // (passive) accept a connection from another pin
    STDMETHODIMP ReceiveConnection(
        IPin * pConnector,      // this is the initiating connecting pin
        const AM_MEDIA_TYPE *pmt   // this is the media type we will exchange
    );

    STDMETHODIMP Disconnect();

    STDMETHODIMP ConnectedTo(IPin **pPin);

    STDMETHODIMP ConnectionMediaType(AM_MEDIA_TYPE *pmt);

    STDMETHODIMP QueryPinInfo(
        PIN_INFO * pInfo
    );

    STDMETHODIMP QueryDirection(
        PIN_DIRECTION * pPinDir
    );

    STDMETHODIMP QueryId(
        LPWSTR * Id
    );

    // does the pin support this media type
    STDMETHODIMP QueryAccept(
        const AM_MEDIA_TYPE *pmt
    );

    // return an enumerator for this pins preferred media types
    STDMETHODIMP EnumMediaTypes(
        IEnumMediaTypes **ppEnum
    );

    // return an array of IPin* - the pins that this pin internally connects to
    // All pins put in the array must be AddReffed (but no others)
    // Errors: "Can't say" - FAIL, not enough slots - return S_FALSE
    // Default: return E_NOTIMPL
    // The filter graph will interpret NOT_IMPL as any input pin connects to
    // all visible output pins and vice versa.
    // apPin can be NULL if nPin==0 (not otherwise).
    STDMETHODIMP QueryInternalConnections(
        IPin* *apPin,     // array of IPin*
        ULONG *nPin       // on input, the number of slots
                          // on output  the number of pins
    ) { return E_NOTIMPL; }

    // Called when no more data will be sent
    STDMETHODIMP EndOfStream(void);

    // Begin/EndFlush still PURE

    // NewSegment notifies of the start/stop/rate applying to the data
    // about to be received. Default implementation records data and
    // returns S_OK.
    // Override this to pass downstream.
    STDMETHODIMP NewSegment(
                    REFERENCE_TIME tStart,
                    REFERENCE_TIME tStop,
                    double dRate);

    //================================================================================
    // IQualityControl methods
    //================================================================================

    STDMETHODIMP Notify(IBaseFilter * pSender, Quality q);

    STDMETHODIMP SetSink(IQualityControl * piqc);

    // --- helper methods ---

    // Returns true if the pin is connected. false otherwise.
    BOOL IsConnected(void) {return (m_Connected != NULL); };
    // Return the pin this is connected to (if any)
    IPin * GetConnected() { return m_Connected; };

    // Check if our filter is currently stopped
    BOOL IsStopped() {
        return (m_pFilter->m_State == State_Stopped);
    };

    // find out the current type version (used by enumerators)
    virtual LONG GetMediaTypeVersion();
    void IncrementTypeVersion();

    // switch the pin to active (paused or running) mode
    // not an error to call this if already active
    virtual HRESULT Active(void);

    // switch the pin to inactive state - may already be inactive
    virtual HRESULT Inactive(void);

    // Notify of Run() from filter
    virtual HRESULT Run(REFERENCE_TIME tStart);

    // check if the pin can support this specific proposed type and format
    virtual HRESULT CheckMediaType(const CMediaType *) PURE;

    // set the connection to use this format (previously agreed)
    virtual HRESULT SetMediaType(const CMediaType *);

    // check that the connection is ok before verifying it
    // can be overridden eg to check what interfaces will be supported.
    virtual HRESULT CheckConnect(IPin *);

    // Set and release resources required for a connection
    virtual HRESULT BreakConnect();
    virtual HRESULT CompleteConnect(IPin *pReceivePin);

    // returns the preferred formats for a pin
    virtual HRESULT GetMediaType(int iPosition,CMediaType *pMediaType);

    // access to NewSegment values
    REFERENCE_TIME CurrentStopTime() {
        return m_tStop;
    }
    REFERENCE_TIME CurrentStartTime() {
        return m_tStart;
    }
    double CurrentRate() {
        return m_dRate;
    }

    //  Access name
    LPWSTR Name() { return m_pName; };

    //  Can reconnectwhen active?
    void SetReconnectWhenActive(bool bCanReconnect)
    {
        m_bCanReconnectWhenActive = bCanReconnect;
    }

    bool CanReconnectWhenActive()
    {
        return m_bCanReconnectWhenActive;
    }

protected:
    STDMETHODIMP DisconnectInternal();
};

在CBasePin实现的成员函数中，有3个与Filter的状态转换相对应。

// 转换pin到活动状态(暂停或运行)
  // not an error to call this if already active
  virtual HRESULT Active(void);

  // 转换pin到不活动状态 - 可能已经处于非活动状态
  virtual HRESULT Inactive(void);

  // 通知运行filter 的 Run()
  virtual HRESULT Run(REFERENCE_TIME tStart);

 

我们来看一下Filter的Stop的实现，实际上就是调用Filter的所有pin的Inactive函数

STDMETHODIMP
CBaseFilter::Stop()
{
    CAutoLock cObjectLock(m_pLock);
    HRESULT hr = NOERROR;

    // 通知所有pin改变状态
    if (m_State != State_Stopped) {
        int cPins = GetPinCount();
        for (int c = 0; c < cPins; c++) {

            CBasePin *pPin = GetPin(c);

            // Disconnected pins are not activated - this saves pins worrying
            // about this state themselves. We ignore the return code to make
            // sure everyone is inactivated regardless. The base input pin
            // class can return an error if it has no allocator but Stop can
            // be used to resync the graph state after something has gone bad
            // 仅在完成连接的pin上调用Inactive函数
            // 如果Inactive函数返回一个错误值，则暂时忽略，
            // 以便所有Pin都有机会被调用Inactive
            if (pPin->IsConnected()) {
                HRESULT hrTmp = pPin->Inactive();
                if (FAILED(hrTmp) && SUCCEEDED(hr)) {
                    hr = hrTmp;
                }
            }
        }
    }


    m_State = State_Stopped;
    return hr;
}

 

在实际开发Filter的过程中，很有可能重写CBasePin::Inactive、 CBasePin::Active和CBasePin::Run这3个函数，以进行必要的初始化、释放资源等。

CBasePin类的使用方法如下：

（1） 从CBasePin派生一个子类；

（2） 实现纯虚函数CBasePIn::CheckMediaType,进行Pin连接时的媒体类型检查；

（3） 实现纯虚函数CBasePin::GetMediaType，提供Pin上的首选媒体类型。

（4） 实现IPin::BeginFlush和IPin::EndFlush两个函数。

（5） 可能需要重写的函数包括

CBasePin::Active()  实现资源分配

CBasePin::Inactive  实现资源释放

CBasePin::Run  在Filter运行前进行一些初始化

CBasePin::CheckConnect  连接时检查，如查询对方Pin上是否支持某个特殊接口

CBasePin::BreakConnect 断开连接，并进行必要的资源释放

CBasePin::CompleteConnect  完成连接时被调用，可以在这个函数中获得当前连接的媒体类型参数

CBasePin::EndOfStream 当上流数据全部传送完毕后被调用。

                    如果这个是Transform Filter，则将EndOfStream继续入下传送；

                   如果是Renderer Filter，需要向Filter Graph Manager发送一个EC_COMPLETE事件

CBasePin::Noftify  直接响应质量控制。

eg:

// CAsyncOutputPin实现了一个输出Pin
// 继承自IAsyncReader、CBasePin,这是对拉模式的Source Filter的基本要求
/* IAsyncReader接口方法及描述如下：
BeginFlush  放弃所有正在进行的数据读取
EndFlush    与BeginFlush配对，标示Flush过程结束
Length      得到数据总长度和当前可以读取的长度
RequestAlloctor 要求一个输入Pin上的Sample管理器
Request     发出一个数据请求
SyncReadAligned 同步读取数据(边界对齐)
SyncRead    同步读取数据
WaitForNext 等待一个请求的完成
======================================================================
可以看出CAsyOutputPin类上实现的IAsyncReader的各个接口方法，都“委托”
给了CAsyncIo类对象的同名成员函数
*/
class CAsyncOutputPin
  : public IAsyncReader,
    public CBasePin
{
protected:
    CAsyncReader* m_pReader;
    CAsyncIo * m_pIo;

    //  This is set every time we're asked to return an IAsyncReader
    //  interface
    //  This allows us to know if the downstream pin can use
    //  this transport, otherwise we can hook up to thinks like the
    //  dump filter and nothing happens
    BOOL         m_bQueriedForAsyncReader;

    HRESULT InitAllocator(IMemAllocator **ppAlloc);

public:
    // constructor and destructor
    CAsyncOutputPin(
        HRESULT * phr,
        CAsyncReader *pReader,
        CAsyncIo *pIo,
        CCritSec * pLock);

    ~CAsyncOutputPin();

    // --- CUnknown ---

    // need to expose IAsyncReader
    DECLARE_IUNKNOWN
    STDMETHODIMP NonDelegatingQueryInterface(REFIID, void**);

    // --- IPin methods ---
    STDMETHODIMP Connect(
        IPin * pReceivePin,
        const AM_MEDIA_TYPE *pmt   // optional media type
    );

    // --- CBasePin methods ---

    // return the types we prefer - this will return the known
    // file type
    HRESULT GetMediaType(int iPosition, CMediaType *pMediaType);

    // can we support this type?
    HRESULT CheckMediaType(const CMediaType* pType);

    // Clear the flag so we see if IAsyncReader is queried for
    HRESULT CheckConnect(IPin *pPin)
    {
        m_bQueriedForAsyncReader = FALSE;
        return CBasePin::CheckConnect(pPin);
    }

    // See if it was asked for
    HRESULT CompleteConnect(IPin *pReceivePin)
    {
        if (m_bQueriedForAsyncReader) {
            return CBasePin::CompleteConnect(pReceivePin);
        } else {

#ifdef VFW_E_NO_TRANSPORT
            return VFW_E_NO_TRANSPORT;
#else
            return E_FAIL;
#endif
        }
    }

    //  Remove our connection status
    HRESULT BreakConnect()
    {
        m_bQueriedForAsyncReader = FALSE;
        return CBasePin::BreakConnect();
    }

    // --- IAsyncReader methods ---
    // pass in your preferred allocator and your preferred properties.
    // method returns the actual allocator to be used. Call GetProperties
    // on returned allocator to learn alignment and prefix etc chosen.
    // this allocator will be not be committed and decommitted by
    // the async reader, only by the consumer.
    STDMETHODIMP RequestAllocator(
                      IMemAllocator* pPreferred,
                      ALLOCATOR_PROPERTIES* pProps,
                      IMemAllocator ** ppActual);

    // queue a request for data.
    // media sample start and stop times contain the requested absolute
    // byte position (start inclusive, stop exclusive).
    // may fail if sample not obtained from agreed allocator.
    // may fail if start/stop position does not match agreed alignment.
    // samples allocated from source pin's allocator may fail
    // GetPointer until after returning from WaitForNext.
    STDMETHODIMP Request(
                     IMediaSample* pSample,
                     DWORD_PTR dwUser);         // user context

    // block until the next sample is completed or the timeout occurs.
    // timeout (millisecs) may be 0 or INFINITE. Samples may not
    // be delivered in order. If there is a read error of any sort, a
    // notification will already have been sent by the source filter,
    // and STDMETHODIMP will be an error.
    STDMETHODIMP WaitForNext(
                      DWORD dwTimeout,
                      IMediaSample** ppSample,  // completed sample
                      DWORD_PTR * pdwUser);     // user context

    // sync read of data. Sample passed in must have been acquired from
    // the agreed allocator. Start and stop position must be aligned.
    // equivalent to a Request/WaitForNext pair, but may avoid the
    // need for a thread on the source filter.
    STDMETHODIMP SyncReadAligned(
                      IMediaSample* pSample);


    // sync read. works in stopped state as well as run state.
    // need not be aligned. Will fail if read is beyond actual total
    // length.
    STDMETHODIMP SyncRead(
                      LONGLONG llPosition,  // absolute file position
                      LONG lLength,         // nr bytes required
                      BYTE* pBuffer);       // write data here

    // return total length of stream, and currently available length.
    // reads for beyond the available length but within the total length will
    // normally succeed but may block for a long period.
    STDMETHODIMP Length(
                      LONGLONG* pTotal,
                      LONGLONG* pAvailable);

    // cause all outstanding reads to return, possibly with a failure code
    // (VFW_E_TIMEOUT) indicating they were cancelled.
    // these are defined on IAsyncReader and IPin
    STDMETHODIMP BeginFlush(void);
    STDMETHODIMP EndFlush(void);

};

5、 CBaseInputPin和CBaseOutputPin

 从CBasePin类派生的，也是很基本的输入或输出pin。

它们的实现可参见 amfilter.cpp

CBaseInputPin实现了IMemInputPin（用于推模式的数据传送），

而CBaseOutputPin主要完成了传送数据所使用的Sample管理器（Allocator）的协商，并重写了CBasePin::Active（用于实际的Sample内存分配）

以及CBasePin::Inactive（用于Sample内存的释放）

class AM_NOVTABLE CBaseInputPin : public CBasePin,
                                  public IMemInputPin
{

protected:

    IMemAllocator *m_pAllocator;    // Default memory allocator

    // allocator is read-only, so received samples
    // cannot be modified (probably only relevant to in-place
    // transforms
    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;

public:

    CBaseInputPin(
        TCHAR *pObjectName,
        CBaseFilter *pFilter,
        CCritSec *pLock,
        HRESULT *phr,
        LPCWSTR pName);
#ifdef UNICODE
    CBaseInputPin(
        CHAR *pObjectName,
        CBaseFilter *pFilter,
        CCritSec *pLock,
        HRESULT *phr,
        LPCWSTR pName);
#endif
    virtual ~CBaseInputPin();

    DECLARE_IUNKNOWN

    // override this to publicise our interfaces
    STDMETHODIMP NonDelegatingQueryInterface(REFIID riid, void **ppv);

    // return the allocator interface that this input pin
    // would like the output pin to use
    STDMETHODIMP GetAllocator(IMemAllocator ** ppAllocator);

    // tell the input pin which allocator the output pin is actually
    // going to use.
    STDMETHODIMP NotifyAllocator(
                    IMemAllocator * pAllocator,
                    BOOL bReadOnly);

    // do something with this media sample
    STDMETHODIMP Receive(IMediaSample *pSample);

    // do something with these media samples
    STDMETHODIMP ReceiveMultiple (
        IMediaSample **pSamples,
        long nSamples,
        long *nSamplesProcessed);

    // See if Receive() blocks
    STDMETHODIMP ReceiveCanBlock();

    // Default handling for BeginFlush - call at the beginning
    // of your implementation (makes sure that all Receive calls
    // fail). After calling this, you need to free any queued data
    // and then call downstream.
    STDMETHODIMP BeginFlush(void);

    // default handling for EndFlush - call at end of your implementation
    // - before calling this, ensure that there is no queued data and no thread
    // pushing any more without a further receive, then call downstream,
    // then call this method to clear the m_bFlushing flag and re-enable
    // receives
    STDMETHODIMP EndFlush(void);

    // this method is optional (can return E_NOTIMPL).
    // 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);

    // Release the pin's allocator.
    HRESULT BreakConnect();

    // helper method to check the read-only flag
    BOOL IsReadOnly() {
        return m_bReadOnly;
    };

    // helper method to see if we are flushing
    BOOL IsFlushing() {
        return m_bFlushing;
    };

    //  Override this for checking whether it's OK to process samples
    //  Also call this from EndOfStream.
    virtual HRESULT CheckStreaming();

    // Pass a Quality notification on to the appropriate sink
    HRESULT PassNotify(Quality& q);


    //================================================================================
    // IQualityControl methods (from CBasePin)
    //================================================================================

    STDMETHODIMP Notify(IBaseFilter * pSender, Quality q);

    // no need to override:
    // STDMETHODIMP SetSink(IQualityControl * piqc);


    // switch the pin to inactive state - may already be inactive
    virtual HRESULT Inactive(void);

    // Return sample properties pointer
    AM_SAMPLE2_PROPERTIES * SampleProps() {
        ASSERT(m_SampleProps.cbData != 0);
        return &m_SampleProps;
    }

};

 

 

class  AM_NOVTABLE CBaseOutputPin : public CBasePin
{

protected:

    IMemAllocator *m_pAllocator;
    IMemInputPin *m_pInputPin;        // interface on the downstreaminput pin
                                      // set up in CheckConnect when we connect.

public:

    CBaseOutputPin(
        TCHAR *pObjectName,
        CBaseFilter *pFilter,
        CCritSec *pLock,
        HRESULT *phr,
        LPCWSTR pName);
#ifdef UNICODE
    CBaseOutputPin(
        CHAR *pObjectName,
        CBaseFilter *pFilter,
        CCritSec *pLock,
        HRESULT *phr,
        LPCWSTR pName);
#endif
    // override CompleteConnect() so we can negotiate an allocator
    virtual HRESULT CompleteConnect(IPin *pReceivePin);

    // negotiate the allocator and its buffer size/count and other properties
    // Calls DecideBufferSize to set properties
    virtual HRESULT DecideAllocator(IMemInputPin * pPin, IMemAllocator ** pAlloc);

    // override this to set the buffer size and count. Return an error
    // if the size/count is not to your liking.
    // The allocator properties passed in are those requested by the
    // input pin - use eg the alignment and prefix members if you have
    // no preference on these.
    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);

    // deliver a filled-in sample to the connected input pin
    // note - you need to release it after calling this. The receiving
    // pin will addref the sample if it needs to hold it beyond the
    // call.
    virtual HRESULT Deliver(IMediaSample *);

    // override this to control the connection
    virtual HRESULT InitAllocator(IMemAllocator **ppAlloc);
    HRESULT CheckConnect(IPin *pPin);
    HRESULT BreakConnect();

    // override to call Commit and Decommit
    HRESULT Active(void);
    HRESULT Inactive(void);

    // we have a default handling of EndOfStream which is to return
    // an error, since this should be called on input pins only
    STDMETHODIMP EndOfStream(void);

    // called from elsewhere in our filter to pass EOS downstream to
    // our connected input pin
    virtual HRESULT DeliverEndOfStream(void);

    // same for Begin/EndFlush - we handle Begin/EndFlush since it
    // is an error on an output pin, and we have Deliver methods to
    // call the methods on the connected pin
    STDMETHODIMP BeginFlush(void);
    STDMETHODIMP EndFlush(void);
    virtual HRESULT DeliverBeginFlush(void);
    virtual HRESULT DeliverEndFlush(void);

    // deliver NewSegment to connected pin - you will need to
    // override this if you queue any data in your output pin.
    virtual HRESULT DeliverNewSegment(
                        REFERENCE_TIME tStart,
                        REFERENCE_TIME tStop,
                        double dRate);

    //================================================================================
    // IQualityControl methods
    //================================================================================

    // All inherited from CBasePin and not overridden here.
    // STDMETHODIMP Notify(IBaseFilter * pSender, Quality q);
    // STDMETHODIMP SetSink(IQualityControl * piqc);
};

 CBaseInputPin类的使用方法（派生一个子类，并且至少需要重写以下函数）如下：

（1） CBaseInputPin::BeginFlush

（2） CBaseInputPin::EndFlush

（3） CBaseInputPin::Receive

（4） CBaseInputPin::CheckMediaType

（5） CBaseInputPin::GetMediaType

eg:

class CRendererInputPin : public CBaseInputPin
{
protected:

    CBaseRenderer *m_pRenderer;

public:

    CRendererInputPin(CBaseRenderer *pRenderer,
                      HRESULT *phr,
                      LPCWSTR Name);

    // Overriden from the base pin classes

    HRESULT BreakConnect();
    HRESULT CompleteConnect(IPin *pReceivePin);
    HRESULT SetMediaType(const CMediaType *pmt);
    HRESULT CheckMediaType(const CMediaType *pmt);
    HRESULT Active();
    HRESULT Inactive();

    // Add rendering behaviour to interface functions

    STDMETHODIMP QueryId(LPWSTR *Id);
    STDMETHODIMP EndOfStream();
    STDMETHODIMP BeginFlush();
    STDMETHODIMP EndFlush();
    STDMETHODIMP Receive(IMediaSample *pMediaSample);

    // Helper
    IMemAllocator inline *Allocator() const
    {
        return m_pAllocator;
    }
};

 

CBaseOutputPin类的使用方法（派生一个子类，并且最少需要重写以下函数）如下：

（1） 重写CBasePin::CheckMediaType进行连接时媒体类型的检查；

（2） 实现纯虚函数CBaseOutputPin::DecideBufferSize,决定Sample内存的大小；

（3） 重写CBasePin::GetMediaType, 提供Pin 上的首选媒体类型。

 

class CTransformOutputPin : public CBaseOutputPin
{
    friend class CTransformFilter;

protected:
    CTransformFilter *m_pTransformFilter;

public:

    // implement IMediaPosition by passing upstream
    IUnknown * m_pPosition;

    CTransformOutputPin(
        TCHAR *pObjectName,
        CTransformFilter *pTransformFilter,
        HRESULT * phr,
        LPCWSTR pName);
#ifdef UNICODE
    CTransformOutputPin(
        CHAR *pObjectName,
        CTransformFilter *pTransformFilter,
        HRESULT * phr,
        LPCWSTR pName);
#endif
    ~CTransformOutputPin();

    // override to expose IMediaPosition
    STDMETHODIMP NonDelegatingQueryInterface(REFIID riid, void **ppv);

    // --- CBaseOutputPin ------------

    STDMETHODIMP QueryId(LPWSTR * Id)
    {
        return AMGetWideString(L"Out", Id);
    }

    // Grab and release extra interfaces if required

    HRESULT CheckConnect(IPin *pPin);
    HRESULT BreakConnect();
    HRESULT CompleteConnect(IPin *pReceivePin);

    // check that we can support this output type
    HRESULT CheckMediaType(const CMediaType* mtOut);

    // set the connection media type
    HRESULT SetMediaType(const CMediaType *pmt);

    // called from CBaseOutputPin during connection to ask for
    // the count and size of buffers we need.
    HRESULT DecideBufferSize(
                IMemAllocator * pAlloc,
                ALLOCATOR_PROPERTIES *pProp);

    // returns the preferred formats for a pin
    HRESULT GetMediaType(int iPosition,CMediaType *pMediaType);

    // inherited from IQualityControl via CBasePin
    STDMETHODIMP Notify(IBaseFilter * pSender, Quality q);

    // Media type
public:
    CMediaType& CurrentMediaType() { return m_mt; };
};

 ===================================================================

如果开发的是一个Transform Filter，Filter的父类很多时候都是选择CTransformFilter或CTransInPlaceFilter，这种Filter的开发相对简单。

但有时，Filter框架不得不选择CBaseFilter、 CBaseInputPin、CBaseOutputFilter等类来实现，这就有点麻烦了。

这时候可以参考CTransformFilter、CTransformInputPin、CTransformOutputPin对上述3上基类的使用，以此来指导Filter的开发。

 ===================================================================

6、 CSource

DirectShow SDK还提供了其他更加实用的Filter类，如：

CSource、CTransformFilter、CTransInPlaceFilter、CVideoTransformFilter、 CBaseRender、CBase Video Render等。

它们的继承关系如图：

如上图所示，CSource类（参见source.cpp的实现）直接从CaseFilter中继承而来，一般作为推模式Source Filter的父类。

CSource类的使用方法如下：

（1）从CSource类中派生一个新的Filter类；

（2）在新的Filter类的构造函数中创建各个CSourceStream类实例（CSourceStream类的构造函数会自动将该Pin加入Filter中，并在析构函数中自动删除）；

（3）使用CSource::pStateLock函数返回的同步对象进行Filter对象上的多线程同步。

注意： 使用CSource作为Filter父类的Filter未必就是Source Filter。在有些开发Transform Filter的应用中，输出Pin需要使用独立的线程。（即与输入Pin上传送数据

              不同的线程）传关，也可以考虑使用CSource。

eg: 参照我的另一篇文章：  

class CPushSourceBitmap : public CSource
{

private:
    // Constructor is private because you have to use CreateInstance
    CPushSourceBitmap(IUnknown *pUnk, HRESULT *phr);
    ~CPushSourceBitmap();

    CPushPinBitmap *m_pPin;

public:
    static CUnknown * WINAPI CreateInstance(IUnknown *pUnk, HRESULT *phr);

};

 

CPushSourceBitmap::CPushSourceBitmap(IUnknown *pUnk, HRESULT *phr)
           : CSource(NAME("PushSourceBitmap"), pUnk, CLSID_PushSourceBitmap)
{
    // The pin magically adds itself to our pin array.
    m_pPin = new CPushPinBitmap(phr, this);

    if (phr)
    {
        if (m_pPin == NULL)
            *phr = E_OUTOFMEMORY;
        else
            *phr = S_OK;
    }
}

7 、  CSourceStream

CSource实际上继承自CBaseFilter，提供了一个“推”数据的能力，这种Filter至少有一个输出

Pin采用了CSourecStream类（或CSourceStream的子类）。如下图所示：

CSourceStream上实现了一个线程（CSourceStream从CAMThread类继承而来），Sample数据就是靠这个线程向一线Filter发送的。

CSourceStream类的使用方法如下：

（1）从CSourceStream派生一个输出Pin类；

（2）重写CSourceStream::GetMediaType，提供输出Pin上的首选媒体类型；

（3）重写CSourceStream::CheckMediaType，进行连续时媒体类型的检查；（可选）

（4）实现CBaseOutPin::DecideBufferSize，决定Sample内存的大小；

（5）实现CSourceStream::FillBuffer，为即将传送出去的Sample 填充数据；

（6）可选地实现CSourceStream::OnThreadCreate、CSourceSream::OnThreadDestroy、CSourceStream::OnThreadStartPlay等函数，

进行适当时节的初始化、资源管理等操作。

eg: 参照我的另一篇文章：  

class CPushPinBitmap : public CSourceStream
{
protected:

    int m_FramesWritten;                // To track where we are in the file
    BOOL m_bZeroMemory;                 // Do we need to clear the buffer?
    CRefTime m_rtSampleTime;            // The time stamp for each sample

    BITMAPINFO *m_pBmi;                 // Pointer to the bitmap header
    DWORD       m_cbBitmapInfo;         // Size of the bitmap header

    // File opening variables
    HANDLE m_hFile;                     // Handle returned from CreateFile
    BYTE * m_pFile;                     // Points to beginning of file buffer
    BYTE * m_pImage;                    // Points to pixel bits

    int m_iFrameNumber;
    const REFERENCE_TIME m_rtFrameLength;

    CCritSec m_cSharedState;            // Protects our internal state
    CImageDisplay m_Display;            // Figures out our media type for us

public:

    CPushPinBitmap(HRESULT *phr, CSource *pFilter);
    ~CPushPinBitmap();

    // Override the version that offers exactly one media type
    HRESULT GetMediaType(CMediaType *pMediaType);
    HRESULT DecideBufferSize(IMemAllocator *pAlloc, ALLOCATOR_PROPERTIES *pRequest);
    HRESULT FillBuffer(IMediaSample *pSample);

    // Quality control
    // Not implemented because we aren't going in real time.
    // If the file-writing filter slows the graph down, we just do nothing, which means
    // wait until we're unblocked. No frames are ever dropped.
    STDMETHODIMP Notify(IBaseFilter *pSelf, Quality q)
    {
        return E_FAIL;
    }

};

8、 CTransformFilter

 CTransformFilter类是开发Transform Filter最基本的类，也是最常用到的类。结构如下：

它有一个输入Pin和一个输出Pin，分别使用CTransformInputPin类和CTransformOutputPin类。

 

从图4.8和图4.9可以看出，

CTransformFilter从CBaseFilter继承而来，

CTransformInputPin从CBaseInputPin继承而来，

CTransformOutputPin从CBaseOutputPin继承而来。另个，在CTransformOutputPin上还实现了IMdiaSeeking 和 IMediaPosition接口。

（其实，CTransformOutputPin并没有真正实现各个Seek操作。在实际的Seek操作请发生时，CTransformOutpPin会将这些操作请求转发给上一级Filter的输出Pin）。

CTransformFilter实现的最大特征是，它将Pin上必须实现的函数都“委托”到了Filter上（Pin上必须实现的函数在Filter上有类似的函数定义）。

一般无须重写输入和输出Pin类，而只须在Filter上实现相应的函数就行了）。

提示：CTransformFilter默认在GetPin函数实现中创建输入和输出Pin。因此，如果重写了自己的输入或输出Pin类，需要重写GetPin函数。

CTransformFilter类的使用方法（派生一个Filter子类，且最少需要重写以下函数）：

（1）CTransformFilter::CheckInputType

（2）CTransformFilter::CheckTransform

（3）CTransformFilter::DecideBufferSize

（4）CTransformFilter::GetMeiaType

（5）CTransformFilter::Transform

eg:CVideoTransformFilter虽然没有实现上面五个函数，但CVideoTransformFilter 的继承类去实现它们。

class CVideoTransformFilter : public CTransformFilter
{
  public:

    CVideoTransformFilter(TCHAR *, LPUNKNOWN, REFCLSID clsid);
    ~CVideoTransformFilter();
    HRESULT EndFlush();

    // =================================================================
    // ----- override these bits ---------------------------------------
    // =================================================================
    // The following methods are in CTransformFilter which is inherited.
    // They are mentioned here for completeness
    //
    // These MUST be supplied in a derived class
    //
    // NOTE:
    // virtual HRESULT Transform(IMediaSample * pIn, IMediaSample *pOut);
    // virtual HRESULT CheckInputType(const CMediaType* mtIn) PURE;
    // virtual HRESULT CheckTransform
    //     (const CMediaType* mtIn, const CMediaType* mtOut) PURE;
    // static CCOMObject * CreateInstance(LPUNKNOWN, HRESULT *);
    // virtual HRESULT DecideBufferSize
    //     (IMemAllocator * pAllocator, ALLOCATOR_PROPERTIES *pprop) PURE;
    // virtual HRESULT GetMediaType(int iPosition, CMediaType *pMediaType) PURE;
    //
    // These MAY also be overridden
    //
    // virtual HRESULT StopStreaming();
    // virtual HRESULT SetMediaType(PIN_DIRECTION direction,const CMediaType *pmt);
    // virtual HRESULT CheckConnect(PIN_DIRECTION dir,IPin *pPin);
    // virtual HRESULT BreakConnect(PIN_DIRECTION dir);
    // virtual HRESULT CompleteConnect(PIN_DIRECTION direction,IPin *pReceivePin);
    // virtual HRESULT EndOfStream(void);
    // virtual HRESULT BeginFlush(void);
    // virtual HRESULT EndFlush(void);
    // virtual HRESULT NewSegment
    //     (REFERENCE_TIME tStart,REFERENCE_TIME tStop,double dRate);
#ifdef PERF

    // If you override this - ensure that you register all these ids
    // as well as any of your own,
    virtual void RegisterPerfId() {
        m_idSkip        = MSR_REGISTER(TEXT("Video Transform Skip frame"));
        m_idFrameType   = MSR_REGISTER(TEXT("Video transform frame type"));
        m_idLate        = MSR_REGISTER(TEXT("Video Transform Lateness"));
        m_idTimeTillKey = MSR_REGISTER(TEXT("Video Transform Estd. time to next key"));
        CTransformFilter::RegisterPerfId();
    }
#endif

  protected:

    // =========== QUALITY MANAGEMENT IMPLEMENTATION ========================
    // Frames are assumed to come in three types:
    // Type 1: an AVI key frame or an MPEG I frame.
    //        This frame can be decoded with no history.
    //        Dropping this frame means that no further frame can be decoded
    //        until the next type 1 frame.
    //        Type 1 frames are sync points.
    // Type 2: an AVI non-key frame or an MPEG P frame.
    //        This frame cannot be decoded unless the previous type 1 frame was
    //        decoded and all type 2 frames since have been decoded.
    //        Dropping this frame means that no further frame can be decoded
    //        until the next type 1 frame.
    // Type 3: An MPEG B frame.
    //        This frame cannot be decoded unless the previous type 1 or 2 frame
    //        has been decoded AND the subsequent type 1 or 2 frame has also
    //        been decoded.  (This requires decoding the frames out of sequence).
    //        Dropping this frame affects no other frames.  This implementation
    //        does not allow for these.  All non-sync-point frames are treated
    //        as being type 2.
    //
    // The spacing of frames of type 1 in a file is not guaranteed.  There MUST
    // be a type 1 frame at (well, near) the start of the file in order to start
    // decoding at all.  After that there could be one every half second or so,
    // there could be one at the start of each scene (aka "cut", "shot") or
    // there could be no more at all.
    // If there is only a single type 1 frame then NO FRAMES CAN BE DROPPED
    // without losing all the rest of the movie.  There is no way to tell whether
    // this is the case, so we find that we are in the gambling business.
    // To try to improve the odds, we record the greatest interval between type 1s
    // that we have seen and we bet on things being no worse than this in the
    // future.

    // You can tell if it's a type 1 frame by calling IsSyncPoint().
    // there is no architected way to test for a type 3, so you should override
    // the quality management here if you have B-frames.

    int m_nKeyFramePeriod; // the largest observed interval between type 1 frames
                           // 1 means every frame is type 1, 2 means every other.

    int m_nFramesSinceKeyFrame; // Used to count frames since the last type 1.
                                // becomes the new m_nKeyFramePeriod if greater.

    BOOL m_bSkipping;           // we are skipping to the next type 1 frame

#ifdef PERF
    int m_idFrameType;          // MSR id Frame type.  1=Key, 2="non-key"
    int m_idSkip;               // MSR id skipping
    int m_idLate;               // MSR id lateness
    int m_idTimeTillKey;        // MSR id for guessed time till next key frame.
#endif

    virtual HRESULT StartStreaming();

    HRESULT AbortPlayback(HRESULT hr);  // if something bad happens

    HRESULT Receive(IMediaSample *pSample);

    HRESULT AlterQuality(Quality q);

    BOOL ShouldSkipFrame(IMediaSample * pIn);

    int m_itrLate;              // lateness from last Quality message
                                // (this overflows at 214 secs late).
    int m_tDecodeStart;         // timeGetTime when decode started.
    int m_itrAvgDecode;         // Average decode time in reference units.

    BOOL m_bNoSkip;             // debug - no skipping.

    // We send an EC_QUALITY_CHANGE notification to the app if we have to degrade.
    // We send one when we start degrading, not one for every frame, this means
    // we track whether we've sent one yet.
    BOOL m_bQualityChanged;

    // When non-zero, don't pass anything to renderer until next keyframe
    // If there are few keys, give up and eventually draw something
    int m_nWaitForKey;
};

 

9、 CTransInPlaceFilter

CTransInPlaceFilter是一个“就地”处理的Transform Filter类。结构如下：

与CTransformFilter，CTransInPlaceFilter也有一个输入Pin和一个输出Pin，但使用CTransInPlaceOutputPin类。

 

CTransInPlaceFilter的输入和输出Pin上一般使用相同的媒体类型进行连接，并且使用同一个Sample管理器（如果Filter实现时要修改Sample数据，

而协商达成一致的Sample管理器只读的，那么CTransInPlaceFilter的输入和输出Pin将不得不使用各自的Sample管理器）。

CTransInPlaceFilter类要实现上述的目标，主要依赖于CTransInPlaceFilter::CompleteConnect、CTransInPlaceInputPin::GetAllocator和

CTransInPlaceInputPin::NotifyAlocator的函数实现。代码如下：

// 当输入或输出Pin完成连接时被调用，
// 经过一个反复重连的过程，来达到输入和输出Pin使用相同的媒体类型的目的
HRESULT CTransInPlaceFilter::CompleteConnect(PIN_DIRECTION dir,IPin *pReceivePin)
{
    UNREFERENCED_PARAMETER(pReceivePin);
    ASSERT(m_pInput);
    ASSERT(m_pOutput);

    // if we are not part of a graph, then don't indirect the pointer
    // this probably prevents use of the filter without a filtergraph
    if (!m_pGraph) {
        return VFW_E_NOT_IN_GRAPH;
    }

    // Always reconnect the input to account for buffering changes
    //
    // Because we don't get to suggest a type on ReceiveConnection
    // we need another way of making sure the right type gets used.
    //
    // One way would be to have our EnumMediaTypes return our output
    // connection type first but more deterministic and simple is to
    // call ReconnectEx passing the type we want to reconnect with
    // via the base class ReconeectPin method.

    // 当输出Pin调用该函数(并且此时输入Pin已连上)时，使用输出Pin上的媒体类型对
    // 输入Pin进行重连接
    if (dir == PINDIR_OUTPUT) {
        if( m_pInput->IsConnected() ) {
            return ReconnectPin( m_pInput, &m_pOutput->CurrentMediaType() );
        }
        return NOERROR;
    }

    ASSERT(dir == PINDIR_INPUT);

    // Reconnect output if necessary

    // 当输入Pin调用该函数(并且此时输出Pin已连上)时，如果输入和输出Pin上使用的
    // 媒体类型不一致，则使用输入Pin上的媒体类型对输出Pin进行重新连接
    if( m_pOutput->IsConnected() ) {

        if (  m_pInput->CurrentMediaType()
           != m_pOutput->CurrentMediaType()
           ) {
            return ReconnectPin( m_pOutput, &m_pInput->CurrentMediaType() );
        }
    }
    return NOERROR;

} // ComnpleteConnect

 

// 当上一级Filter的输出Pin要求我们的输入Pin提供Sample管理器时，
// 如果我们的输出Pin已连接上，则可以取出输出Pin上的Sample管理器提供给上一级
// Filter，以此达到我们的输入和输出Pin使用同一个Sample管理器的目的
STDMETHODIMP CTransInPlaceInputPin::GetAllocator(IMemAllocator ** ppAllocator)
{
    CheckPointer(ppAllocator,E_POINTER);
    ValidateReadWritePtr(ppAllocator,sizeof(IMemAllocator *));
    CAutoLock cObjectLock(m_pLock);

    HRESULT hr;

    if ( m_pTIPFilter->m_pOutput->IsConnected() ) {
        //  Store the allocator we got
        hr = m_pTIPFilter->OutputPin()->ConnectedIMemInputPin()
                                        ->GetAllocator( ppAllocator );
        if (SUCCEEDED(hr)) {
            m_pTIPFilter->OutputPin()->SetAllocator( *ppAllocator );
        }
    }
    else {
        //  Help upstream filter (eg TIP filter which is having to do a copy)
        //  by providing a temp allocator here - we'll never use
        //  this allocator because when our output is connected we'll
        //  reconnect this pin
        hr = CTransformInputPin::GetAllocator( ppAllocator );
    }
    return hr;

} // GetAllocator

 

// 上一级Filter调用该函数，告知输入Pin上到底使用哪一个Sample管理器
// 如果设置进来的Sample管理器是只读的，而我们在Filter中又想修改数据，
// 则我们的Filter不得不最终使用不同的Sample管理器
STDMETHODIMP
CTransInPlaceInputPin::NotifyAllocator(
    IMemAllocator * pAllocator,
    BOOL bReadOnly)
{
    HRESULT hr = S_OK;
    CheckPointer(pAllocator,E_POINTER);
    ValidateReadPtr(pAllocator,sizeof(IMemAllocator));

    CAutoLock cObjectLock(m_pLock);

    m_bReadOnly = bReadOnly;
    //  If we modify data then don't accept the allocator if it's
    //  the same as the output pin's allocator

    //  If our output is not connected just accept the allocator
    //  We're never going to use this allocator because when our
    //  output pin is connected we'll reconnect this pin
    if (!m_pTIPFilter->OutputPin()->IsConnected()) {
        return CTransformInputPin::NotifyAllocator(pAllocator, bReadOnly);
    }

    //  If the allocator is read-only and we're modifying data
    //  and the allocator is the same as the output pin's
    //  then reject
    if (bReadOnly && m_pTIPFilter->m_bModifiesData) {
        IMemAllocator *pOutputAllocator =
            m_pTIPFilter->OutputPin()->PeekAllocator();

        //  Make sure we have an output allocator
        if (pOutputAllocator == NULL) {
            hr = m_pTIPFilter->OutputPin()->ConnectedIMemInputPin()->
                                      GetAllocator(&pOutputAllocator);
            if(FAILED(hr)) {
                hr = CreateMemoryAllocator(&pOutputAllocator);
            }
            if (SUCCEEDED(hr)) {
                m_pTIPFilter->OutputPin()->SetAllocator(pOutputAllocator);
                pOutputAllocator->Release();
            }
        }
        if (pAllocator == pOutputAllocator) {
            hr = E_FAIL;
        } else if(SUCCEEDED(hr)) {
            //  Must copy so set the allocator properties on the output
            ALLOCATOR_PROPERTIES Props, Actual;
            hr = pAllocator->GetProperties(&Props);
            if (SUCCEEDED(hr)) {
                hr = pOutputAllocator->SetProperties(&Props, &Actual);
            }
            if (SUCCEEDED(hr)) {
                if (  (Props.cBuffers > Actual.cBuffers)
                   || (Props.cbBuffer > Actual.cbBuffer)
                   || (Props.cbAlign  > Actual.cbAlign)
                   ) {
                    hr =  E_FAIL;
                }
            }

            //  Set the allocator on the output pin
            if (SUCCEEDED(hr)) {
                hr = m_pTIPFilter->OutputPin()->ConnectedIMemInputPin()
                                       ->NotifyAllocator( pOutputAllocator, FALSE );
            }
        }
    } else {
        hr = m_pTIPFilter->OutputPin()->ConnectedIMemInputPin()
                                   ->NotifyAllocator( pAllocator, bReadOnly );
        if (SUCCEEDED(hr)) {
            m_pTIPFilter->OutputPin()->SetAllocator( pAllocator );
        }
    }

    if (SUCCEEDED(hr)) {

        // It's possible that the old and the new are the same thing.
        // AddRef before release ensures that we don't unload it.
        pAllocator->AddRef();

        if( m_pAllocator != NULL )
            m_pAllocator->Release();

        m_pAllocator = pAllocator;    // We have an allocator for the input pin
    }

    return hr;

} // NotifyAllocator

CTransInPlaceFilter类定义了一个成员变量m_bModifiesData ，用于指示我们在Filter中是否会修改Saple 数据。

这个变量在CTransInPlaceFilter构造函数调用时被默认初始化为true。如果我们确定不会在Filter中修改Sample数据，

那么，将m_bModifiesData设置为false， 可以保证输入和输出Pin连接完成后使用同一个Sample管理器。

 

10、 CVideoTransformFilter

CVieoTransformFilter是一个实现了视频的质量控制的Transform Filter类。其结构如下：

CVieoTransformFilter通过输入Pin上的Receive 函数接收Sample时，能够根据质量消息决定是否丢帧。这个类主要是为开发AVI解码Filter而设计的。

CVieoTransformFilter类的使用基本上与CTransformFilter相同。

 

11、 CBaseRenderer

CBaseRender是最基本的实现Renderer Filter的类。它默认实现了一个使用CRendererInputPin类的输入Pin（Renderer Filter没有输出Pin）。

这两个类的结构如下：

从图中可以看出，CBaseRenderer从CBaseFilter继承而来。另外，CBaseRenderer上还实现了IMediaSeekin和IMediaPosition接口。

CRendererInputPin从CBaseInputPin 继承而来，它把各个主要函数调用都“委托”到Filter上。值得注意的是，当输入Pin接收到EndOfStream调用时，

Renderer Filter 有责任向Filter Graph Manager发送一个EC_COMPLETE事件。

CBaseRenderer类的使用方法（派生一个子类，并至少实现如下函数）如下：

（1）CBaseRenderer::CheckMediaType，用于检查输入Pin连接用的媒体类型；

（2）CBaseRenderer::DoRenderSample，处理当前的Sample。

提示：CBaseRenderer实际上是为了用于播放的Render Filter设计的，对于Sample的安排比较复杂。

如果我们要开发Renderer Filter不播放Sample（比如写文件的Filter、或者负责网络的Filter），Fitler的基类可以选择CBaseFilter，而此时输入Pin最

好选择CRenderedInputPin类派生。

 

12、CBaseVideoRenderer

CBaseVideoRenderer是一个实现Video Renderer类的基类，结构如下：

CBaseVideoRenderer在CBaseRenderer的基础上增加了IQualityControl和IQualProp接口的实现。

其中IQualityControl用于视频质量控制，IQualProp用于在Filter属性页显示一些实时性能参数。CBaseVideoRenderer类的使用方法基本上与CBaseRenderer相同。

 

在DirectShow SDK基类库中，除了上述Filter和Pin类外，还有很多工具类，有了这些类的支持，我们开发Fitler或DirectShow应用程序会更加轻松。

这些类包括： CPullPin、 COutputQueue、  CSourceSeeking  、CEnumPins、 CEnumMediaTypes  、CMemAllocator 、 CMediaSample  、

CBaseReferenceClock  、CMediaType、 CBasePropertyPage  等。

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