Notifies the media sink that the presentation clock is about to start.
HRESULT NotifyPreroll( MFTIME hnsUpcomingStartTime );
The upcoming start time for the presentation clock, in 100-nanosecond units. This time is the same value that will be given to the IMFPresentationClock::Start method when the presentation clock is started.
If this method succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.
After this method is called, the media sink sends any number of MEStreamSinkRequestSample events to request samples, until is has enough preroll data. When it has enough preroll data, the media sink sends an MEStreamSinkPrerolled event. This event signals that the client can start the presentation clock.
During preroll, the media sink can prepare the samples that it receives, so that they are ready to be rendered. It does not actually render any samples until the clock starts.
|Minimum supported client||Windows Vista [desktop apps | UWP apps]|
|Minimum supported server||Windows Server 2008 [desktop apps | UWP apps]|