COutputQueue 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 It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation.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 COutputQueue class implements a queue to deliver media samples.

This class enables an output pin to deliver samples asynchronously. Samples are placed on a queue, and a worker thread delivers them to the input pin. The queue can also hold control messages that indicate a new segment, an end-of-stream notification, or a flush operation.

To use this class, create a COutputQueue object for every output pin on the filter. In the constructor method, specify the input pin connected to that output pin. Using this class, the output pin does not call methods directly on the input pin. Instead, it calls corresponding methods in COutputQueue, as shown in the following table.

Pin Method	COutputQueue Method
IPin::BeginFlush	BeginFlush
IPin::EndFlush	EndFlush
IPin::EndOfStream	EOS
IPin::NewSegment	NewSegment
IMemInputPin::Receive	Receive
IMemInputPin::ReceiveMultiple	ReceiveMultiple

Optionally, you can configure the COutputQueue object to deliver samples synchronously, without a worker thread. The object can also decide at run time whether to use a worker thread, based on the characteristics of the input pin. For more information, see COutputQueue::COutputQueue.

Protected Member Variables	Description
m_pPin	Pointer to the input pin's IPin interface.
m_pInputPin	Pointer to the input pin's IMemInputPin interface.
m_bBatchExact	Flag that specifies whether the object delivers samples in exact batches.
m_lBatchSize	Batch size.
m_List	Media sample queue.
m_hSem	Handle to a semaphore, used by the thread to wait for samples.
m_evFlushComplete	Event that signals when a flush operation has finished.
m_hThread	Handle to the worker thread.
m_ppSamples	Array of samples of size COutputQueue::m_lBatchSize.
m_nBatched	Number of samples currently batched and awaiting processing.
m_lWaiting	Flag that has a nonzero value when the thread is waiting for a sample.
m_bFlushing	Flag that specifies whether the object is performing a flush operation.
m_bTerminate	Flag that specifies whether the thread should terminate.
m_bSendAnyway	Flag to override batch processing.
m_hr	HRESULT value that indicates whether the object will accept samples.
m_hEventPop	Event that is signaled whenever the object removes a sample from the queue.
Protected Methods	Description
InitialThreadProc	Calls the COutputQueue::ThreadProc method when the thread is created.
ThreadProc	Retrieves samples from the queue and delivers them to the input pin.
IsQueued	Determines whether the object is using a worker thread to deliver samples.
QueueSample	Queues a media sample or control message.
IsSpecialSample	Determines whether queued data is a control message.
FreeSamples	Frees all pending samples.
NotifyThread	Notifies the thread that the queue contains data.
Public Methods	Description
COutputQueue	Constructor method.
~COutputQueue	Destructor method.
BeginFlush	Begins a flush operation.
EndFlush	Ends a flush operation.
EOS	Delivers an end-of-stream call to the input pin.
SendAnyway	Delivers any pending samples.
NewSegment	Delivers a new segment to the input pin.
Receive	Delivers a media sample to the input pin.
ReceiveMultiple	Delivers a batch of media samples to the input pin.
Reset	Resets the object so that it can receive more data.
IsIdle	Determines whether the object is waiting for data.
SetPopEvent	Specifies an event that is signaled whenever the object removes a sample from the queue.

Requirements

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