Microsoft DirectX 9.0

IReferenceClock Interface

The IReferenceClock interface provides the reference time for the filter graph.

Filters that can act as a reference clock can expose this interface. It is also exposed by the System Reference Clock. The filter graph manager uses this interface to synchronize the filter graph. Applications can use this interface to retrieve the current reference time, or to request notification of an elapsed time.

For more information, see Time and Clocks in DirectShow.

Filter developers: Implement this interface if you are writing a filter that generates reliable clock times. For example, audio renderers implement this interface, because audio sound boards usually contain a reference clock. Use the CBaseReferenceClock class to implement this interface.

To increase the chances that a non-rendering filter will be selected by the Filter Graph Manager as the reference close, follow these steps:

  1. Implement IReferenceClock in the filter.
  2. Implement IAMFilterMiscFlags in the filter.
  3. Return AM_FILTER_MISC_FLAGS_IS_SOURCE from IAMFilterMiscFlags::GetMiscFlags.
  4. Implement IAMPushSource on all output pins.
  5. Return (* pFlags) = 0 from IAMPushSource::GetPushSourceFlags.
  6. You may return E_NOTIMPL from all other IAMPushSource methods.

In addition to the methods inherited from IUnknown, the IReferenceClock interface exposes the following methods.

Method Description
GetTime Retrieves the current reference time.
AdviseTime Creates a one-shot advise request.
AdvisePeriodic Creates a periodic advise request.
Unadvise Removes a pending advise request.