CSource 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 It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation.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 CSource class is a base class for implementing source filters. A filter derived from CSource contains one or more output pins derived from the CSourceStream class. Each output pin creates a worker thread that pushes media samples downstream.

Note

The CSource class is designed to support the push model for data flow. This class is not recommended for creating file-reader filters. File readers should support the pull model, through the IAsyncReader interface. For more information, see Data Flow for Filter Developers.

Protected Member Variables	Description
m_iPins	Number of pins on the filter.
m_paStreams	Array of pins.
m_cStateLock	Critical section object that protects the filter state.
Public Methods	Description
CSource	Constructor method.
~CSource	Destructor method.
GetPinCount	Retrieves the number of pins on the filter.
GetPin	Retrieves a pin.
pStateLock	Retrieves a pointer to the filter's critical section object.
AddPin	Adds a new output pin to the filter.
RemovePin	Removes a specified pin from the filter.
FindPinNumber	Retrieves the number of a specified pin on the filter.
IBaseFilter Methods	Description
FindPin	Retrieves the pin with the specified identifier.

Remarks

To implement an output pin, do the following:

• Derive a class from CSourceStream.
• Override the CSourceStream::GetMediaType method and possibly the CSourceStream::CheckMediaType method, which validate media types for the pin.
• Implement the CBaseOutputPin::DecideBufferSize method, which returns the pin's buffer requirements.
• Implement the CSourceStream::FillBuffer method, which fills a media sample buffer with data.

To implement the filter, do the following:

• Derive a class from CSource.
• In the constructor, create one or more output pins derived from CSourceStream. The pins automatically add themselves to the filter in their constructor methods, and remove themselves in their destructor methods.

To synchronize the filter state among multiple threads, call the CSource::pStateLock method. This method returns a pointer to the filter-state critical section. Use the CAutoLock class to hold the critical section. From a pin, you can access pStateLock from the pin's CBasePin::m_pFilter member variable, as follows:

CAutoLock lock(m_pFilter->pStateLock());

Requirements

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

See also

Writing Source Filters