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The purpose of the mapper is to help the filter graph manager avoid loading filters when attempting to build a filter graph to render a given media type. By looking at filter properties recorded in the registry, the number of filters that must be loaded and tried can be reduced.
The IFilterMapper::EnumMatchingFiltersmethod returns the enumerator that enumerates the filters that match specific requirements. The enumerator returns descriptors of filters, including the globally unique identifiers (GUIDs) that the Microsoft Win32 CoCreateInstancefunction can instantiate. The filters are not loaded. The IEnumRegFiltersinterface is a Component Object Model (COM) enumerator.
When to Implement
This interface is implemented by the filter mapper and need not be implemented elsewhere.
When to Use
Although the filter graph manager is the primary user of this interface, applications can also use it to determine available filters in the system — for example, to construct a unique filter graph by adding and connecting filters itself, or to allow users to choose from a list of available filters.
Methods in Vtable Order
| IUnknown methods | Description |
|---|---|
| QueryInterface | Returns pointers to supported interfaces. |
| AddRef | Increments the reference count. |
| Release | Decrements the reference count. |
| IEnumRegFilters methods | Description |
| Next | Fills an array with the next filters that meet the requirements. |
| Skip | Skips a specified number of elements in the enumeration sequence. |
| Reset | Makes the Nextmethod start again, beginning at the first filter. |
| Clone | Returns another enumerator containing the same enumeration state as the current one. |