The IReferenceClock interface represents a system reference clock to be implemented by a filter in the filter graph and used by other filters.
When to Implement
Implement this interface if you are writing a filter that generates a system reference clock. Typically, this applies to audio renderer filters because audio sound boards usually contain a reference clock. Use the CBaseReferenceClock class to implement this interface.
When to Use
Use this interface on any filter to obtain reference clock notifications for a duration of elapsed time (both singular and repetitive), or to retrieve the current time.
Methods in Vtable Order
| IUnknown methods | Description |
| QueryInterface | Returns pointers to supported interfaces. |
| AddRef | Increments the reference count. |
| Release | Decrements the reference count. |
| IReferenceClock methods | Description |
| GetTime | Gets the current time. |
| AdviseTime | Requests an asynchronous notification that a duration has elapsed. |
| AdvisePeriodic | Requests an asynchronous, periodic notification that a duration has elapsed. |
| Unadvise | Cancels a request for notification. |
Requests an asynchronous, periodic notification that a duration has elapsed.
HRESULT AdvisePeriodic(
REFERENCE_TIME rtStartTime,
REFERENCE_TIME rtPeriodTime,
HSEMAPHORE hSemaphore,
DWORD * pdwAdviseCookie
);
Returns an HRESULT value.
When the time indicated by rtStartTime is reached, the semaphore whose handle is set as hSemaphore will be released. Thereafter, the semaphore will be released repetitively with a period of rtPeriodTime.
Requests an asynchronous notification that a duration has elapsed.
HRESULT AdviseTime(
REFERENCE_TIME rtBaseTime,
REFERENCE_TIME rtStreamTime,
HEVENT hEvent,
DWORD * pdwAdviseCookie
);
Returns an HRESULT value.
When the time rtBaseTime+rtStreamTime is reached, the event whose handle is hEvent will be set. If the time has already passed, the event will be set immediately.
Retrieves the current time. REFERENCE_TIME is a LONGLONG type and loosely represents the number of 100-nanosecond units that have elapsed since some fixed start time. See Characteristics of a Reference Clock for other requirements on the reference clock.
HRESULT GetTime(
REFERENCE_TIME * pTime
);
Returns an HRESULT value.
Cancels a request for notification. See IReferenceClock::AdviseTime.
HRESULT Unadvise(
DWORD dwAdviseCookie
);
Returns an HRESULT value.
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