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CTransformFilteris an abstract base class that supports a simple transform filter with a single input and a single output. It is derived from the CUnknownclass, and it supports the IBaseFilterinterface. Each pin, declared as Friends in this class, supports the IPininterface and uses the shared memory transport based on the IMemInputPininterface. The filter uses classes derived from the CBaseFilterclass to support IBaseFilter; the CTransformInputPininput pin class is derived from the CBaseInputPinclass, and the CTransformOutputPinoutput pin class is derived from the CBaseOutputPinclass.
Note that, while most member functions in this class are designed to be overridden, the following pure virtual member functions must be overridden.
Protected Data Members
| m_bEOSDelivered | End-of-stream delivery status flag. |
| m_bQualityChanged | Status flag that indicates if the stream has degraded. This is set to TRUE in CTransformFilter::Receiveif the call to the derived class's Transformmember function fails ( CTransformFilter::Receivereturns NOERROR in this case because returning S_FALSE indicates that the end-of-stream has arrived). |
| m_bSampleSkipped | Status flag that indicates if a frame was skipped. |
| m_csFilter | Critical section that protects the filter state. This critical section is held whenever the state is currently changing or might change. It is passed to the CBaseMediaFilterconstructor so that the base class uses it too. |
| m_csReceive | Critical section that is held when processing events that occur on the receiving thread ( CTransformInputPin::Receiveand CTransformInputPin::EndOfStream). |
| m_idTransform | Identifier used for performance measurement. Available only when PERFis defined. |
| m_pInput | Pointer to the input pin class object. |
| m_pOutput | Pointer to the output pin class object. |
Member Functions
| CTransformFilter | Constructs a CTransformFilterobject. |
Overridable Member Functions
| AlterQuality | Receives a quality-control notification from the output pin and provides an opportunity to alter the media stream's quality. |
| BeginFlush | Receives notification of entering the flushing state and passes it downstream. |
| BreakConnect | Informs the derived class when the connection is broken. |
| CheckConnect | Informs the derived class when the connection process is starting. |
| CheckInputType | Verifies that the input pin supports the media type and proposes the media type of the output pin (pure virtual). |
| CheckTransform | Verifies that the input and output pins support the media type (pure virtual). |
| CompleteConnect | Informs the derived class when the connection process has completed. |
| DecideBufferSize | Sets the number and size of buffers required for the transfer (pure virtual). |
| EndFlush | Receives notification of leaving the flushing state and passes it downstream. |
| EndOfStream | Receives an end-of-stream notification and passes it downstream. |
| GetMediaType | Returns one of the media types that the output pin supports (pure virtual). |
| GetPin | Returns the pin for the index specified. |
| GetPinCount | Returns the number of pins on the filter. |
| NewSegment | Informs the derived class that a new segment has started and delivers it downstream. |
| Receive | Receives the media sample, calls the CTransformFilter::Transformmember function, and then delivers the media sample. |
| RegisterPerfId | Registers a performance measurement identifier. |
| SetMediaType | Informs the derived class when the media type is established for the connection. |
| StartStreaming | Informs the derived class that streaming is starting. |
| StopStreaming | Informs the derived class that streaming is ending. |
| Transform | Performs transform operations, reading from the input IMediaSampleinterface and writing the data to the output IMediaSampleinterface (pure virtual). |
Implemented IBaseFilter Methods
| FindPin | Retrieves the pin with the specified identifier. |
| Pause | Transitions the filter to State_Pausedstate if it is not in this state already, and informs the derived class. |
| Stop | Transitions the filter to State_Stoppedstate if it is not in this state already, and informs the derived class. |