CBaseFilter Class

Article
06/30/2006

This is an abstract base class from which all filters are derived. It supports the Component Object Model (COM) IBaseFilter interface and is derived from the CUnknown class. This class supports the enumeration of pins by calling the pure virtual member functions CBaseFilter::GetPin and GetPinCount. These member functions must be overridden by any derived class.

The CBaseFilter class assumes that all the filter's pins are derived from the CBasePin class. CBaseFilter::GetPin must return a pointer to CBasePin.

All member functions in this class that return HRESULT and accept a pointer as a parameter return E_POINTER when passed a null pointer.

Protected Data Members

Member	Description
m_clsid	Class identifier (CLSID) used for serialization using IPersist.
m_pClock	Filter graph's reference clock.
m_pGraph	Pointer to a graph to which this filter belongs.
m_PinVersion	Current version of the pins used on the filter.
m_pLock	Pointer to the critical section used for locking.
m_pName	Filter name.
m_pSink	Pointer to the IMediaEventSink interface on the filter graph manager.
m_State	Current state: running or paused.
m_tStart	Offset from the stream time to the reference time.

Member Functions

Member function	Description
CBaseFilter	Constructs a CBaseFilter object.
GetFilterGraph	Returns the filter graph associated with the filter. This is used in the implementation of CEnumPins.
IncrementPinVersion	Adds 1 to the pin version stored in m_PinVersion.
IsActive	Determines if the filter is currently active (running or paused) or stopped.
NotifyEvent	Sends an event notification to the filter graph.
ReconnectPin	Requests pin for a reconnect.

Overrideable Member Functions

Member function	Description
GetPin	Returns a pointer to the requested pin.
GetPinCount	Returns the number of pins currently available on this object.
GetPinVersion	Returns the current version of the base filter for comparison with the version with which the pin was initialized. This member function can be overridden if pins are being created dynamically.
GetSetupData	Retrieves the registration data associated with the filter.
StreamTime	Returns the current stream time.

Implemented IPersist Methods

Method	Description
GetClassID	Returns the class identifier of this filter.

Implemented IMediaFilter Methods

Method	Description
GetState	Retrieves the current state of the filter.
GetSyncSource	Retrieves the current reference clock in use by this filter.
Pause	Instructs the filter to transition to State_Paused state.
Run	Instructs the filter to transition to State_Running state. Passes a time value to synchronize independent streams.
SetSyncSource	Informs the filter of the reference clock with which it should synchronize activity.
Stop	Instructs the filter to transition to the State_Stopped state.

Implemented IBaseFilter Methods

Method	Description
EnumPins	Provides an enumerator for this pin's preferred media types (implemented by this class).
FindPin	Retrieves the pin with the specified identifier.
JoinFilterGraph	Notifies a filter that it has joined a filter graph (implemented by this class).
QueryFilterInfo	Gets information about the specified filter (implemented by this class).
QueryVendorInfo	Retrieves optional information supplied by a vendor for the specified filter.

Implemented IAMovieSetup Methods

Method	Description
Register	Adds the filter to the registry.
Unregister	Removes the filter from the registry.

Implemented INonDelegatingUnknown Methods

Method	Description
NonDelegatingQueryInterface	Passes out pointers to any interfaces added to the derived filter class.

Requirements

DirectShow applications and DirectShow filters have different include file and link library requirements. See Setting Up the Build Environment for more information.

OS Versions: Windows CE 3.0 and later.
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Last updated on Wednesday, April 13, 2005

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