CBaseFilter class

[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

The CBaseFilter class is an abstract class for implementing filters. To implement a filter using this class, you must perform at least the following steps:

• Derive a new class from CBaseFilter.
• Include member variables that define the pins on the filter. The pins must inherit from the CBasePin class.
• Override the pure virtual method CBaseFilter::GetPin, which retrieves pins on the filter.
• Override the pure virtual method CBaseFilter::GetPinCount, which retrieves the number of pins.
• Provide methods for generating, processing, or rendering media samples.

Several base classes derive from CBaseFilter, including CSource, CBaseRenderer, and CTransformFilter. It is usually easier to implement a filter with one of these specialized classes, rather than use CBaseFilter directly.

Protected Member Variables	Description
m_State	Current state of the filter.
m_pClock	Pointer to the filter's reference clock.
m_tStart	Reference time that corresponds to stream time 0.
m_clsid	Class identifier (CLSID) of the filter.
m_pLock	Pointer to a critical section that is used to serialize state changes.
m_pName	Filter name.
m_pGraph	Pointer to the filter graph manager.
m_pSink	Pointer to the IMediaEventSink interface on the filter graph manager.
m_PinVersion	Current version of the set of pins on this filter.
Public Methods	Description
CBaseFilter	Constructor method.
~ CBaseFilter	Destructor method.
StreamTime	Retrieves the current stream time. Virtual.
IsActive	Determines whether the filter is currently active (running or paused).
IsStopped	Determines whether the filter is currently stopped.
NotifyEvent	Sends an event notification to the filter graph manager.
GetFilterGraph	Retrieves a pointer to the filter graph manager.
ReconnectPin	Breaks an existing pin connection and reconnects it to the same pin, using a specified media type.
GetPinVersion	Retrieves a version number for the set of pins on this filter. Virtual.
IncrementPinVersion	Increments the version number on the set of pins.
GetSetupData	Retrieves the registration data for the filter. Virtual.
Pure Virtual Methods	Description
GetPinCount	Retrieves the number of pins.
GetPin	Retrieves a pin.
IPersist Methods	Description
GetClassID	Retrieves the class identifier.
IMediaFilter Methods	Description
GetState	Retrieves the filter's state (running, stopped, or paused).
SetSyncSource	Sets a reference clock for the filter.
GetSyncSource	Retrieves the reference clock that the filter is using.
Stop	Stops the filter.
Pause	Pauses the filter.
Run	Runs the filter.
IBaseFilter Methods	Description
EnumPins	Enumerates the pins on this filter.
FindPin	Retrieves the pin with the specified identifier.
QueryFilterInfo	Retrieves information about the filter.
JoinFilterGraph	Notifies the filter that it has joined or left a filter graph.
QueryVendorInfo	Retrieves a string containing vendor information.
IAMovieSetup Methods	Description
Register	Adds the filter to the registry.
Unregister	Removes the filter from the registry.

Requirements

Requirement	Value
Header	Amfilter.h (include Streams.h)
Library	Strmbase.lib (retail builds); Strmbasd.lib (debug builds)