The CBaseStreamControlclass implements the IAMStreamControlinterface on input and output pins in a filter graph. This class provides control of the starting and stopping of various components of the stream. Various streams can be turned on or off without affecting the rest of the graph. For example, an audio stream can be turned off while a video stream continues, for muting. Or perhaps a capture stream can be turned off while preview continues to flow. This could be used to assist in frame accuracy when exact capture start or stop times are important.

CBaseStreamControlenables you to specify start and stop times in the StartAtand StopAtmember functions and provides stream information in the GetInfomember function. CBaseStreamControluses the StreamControlStateenumerated data type to describe the various states a stream is in. If a stream is flowing it is indicated by the STREAM_FLOWING setting, otherwise it is in a discarding state indicated by the STREAM_DISCARDING setting.

Filters that need to implement the interface on their own should typically inherit from CBaseStreamControlto obtain an implementation of the StartAt, StopAt, and GetInfomethods. The CBaseStreamControlclass also maintains state information and decides what to do with the sample. To implement your own filter with pins that support CBaseStreamControlyou must:

• Inform the filter object of all state changes through the NotifyFilterStatemember function.
• Inform the filter object of all SetSyncSourcecalls to the filter.
• Inform the filter object when in a flushing state. and when flushing has completed, in the CBaseStreamControl::Flushingmember function.
• Use the CheckStreamStatefunction to make decisions about discarding or passing along samples.
• Make sure output pins set discontinuity flags on the first sample flowed after samples have been discarded.
• Tell your pin what the sink is when your filter joins a filter graph, as shown in the following example.
• STDMETHODIMP CMyFilter::JoinFilterGraph(IFilterGraph * pGraph, LPCWSTR pName)
• {
• HRESULT hr = CBaseFilter::JoinFilterGraph(pGraph, pName);
• if (hr == S_OK)
• m_pMyPin->SetFilterGraph(m_pSink);
• return hr;
• }

  If you are implementing the IAMStreamControlinterface without using CBaseStreamControl, the last two preceding points do not apply.

  For sample code, see the video capture sample in the Samples\Multimedia\DShow\src\vidcap subdirectory of the DirectX Media SDK.

  Member Functions

  CBaseStreamControl	Constructs a CBaseStreamControlobject.
  CheckStreamState	Retrieves a stream's current state.
  Flushing	Notifies the pin when the filter is flushing.
  GetInfo	Retrieves information about the current streaming settings.
  NotifyFilterState	Notifies the pin of what state your filter is in.
  SetFilterGraph	Sets the event sink notification that your filter graph is using.
  SetSyncSource	Identifies the reference clock being used by the graph your filter is in.
  StartAt	Informs the pin when to start sending streaming data.
  StopAt	Informs the pin when to stop processing data and discard any new samples.

  
  

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  Last updated on Friday, May 26, 2006

  © 2004 Microsoft Corporation. All rights reserved.