| Microsoft DirectX 9.0 |
The CheckStreamState method determines whether a media sample should be delivered or discarded.
Syntax
enum StreamControlState CheckStreamState(
IMediaSample *pSample
);
Parameters
pSample
Pointer to the sample's IMediaSample interface.
Return Values
Returns one of the following values.
| Return code | Description |
| STREAM_DISCARDING | Discard this sample. |
| STREAM_FLOWING | Deliver this sample. |
Remarks
Call this method when your pin receives a sample. Deliver the sample only if the return value is STREAM_FLOWING. If the return value is STREAM_DISCARDING, discard the sample.
If the pin discards any samples, it should mark the next sample that it delivers as a discontinuity, by calling the IMediaSample::SetDiscontinuity method.
If your filter implements the IAMDroppedFrames interface to count how many frames it drops, do not count a discarded frame as a dropped frame.
When the return value is STREAM_DISCARDING, the method blocks until the reference time reaches the sample's start time. This prevents your pin from discarding samples too quickly. If the filter is paused, the wait time is infinite, until the filter runs, stops, or flushes data. (Filter state changes and streaming happen on separate threads, so this does not cause any deadlock.)
The CBaseStreamControl::StreamControlState enumeration is defined as follows:
enum StreamControlState{
STREAM_FLOWING = 0x1000,
STREAM_DISCARDING
};
Example Code
The following example assumes that the pin uses a member variable named m_fLastSampleDiscarded to keep track of discontinuities.
CMyPin::Receive(IMediaSample *pSample)
{
if (!pSample) return E_POINTER;
int iStreamState = CheckStreamState(pSample);
if (iStreamState == STREAM_FLOWING)
{
if (m_fLastSampleDiscarded)
pSample->SetDiscontinuity(TRUE);
m_fLastSampleDiscarded = FALSE;
/* Deliver the sample. */
}
else
{
m_fLastSampleDiscarded = TRUE;
// Discard this sample. Do not deliver it.
}
}
See Also