[DirectShow] 038 - Enumerating Filters

最新推荐文章于 2024-05-08 10:07:32 发布

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#filter #graph #reference #null #manager #structure

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本文介绍如何使用IFilterGraph::EnumFilters方法枚举DirectShow过滤器图中的所有过滤器，并通过IBaseFilter::QueryFilterInfo方法获取每个过滤器的名称。

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The Filter Graph Manager supports the IFilterGraph::EnumFilters method, which enumerates all the filters in the filter graph. It returns a pointer to the IEnumFilters interface. The IEnumFilters::Next method retrieves IBaseFilter interface pointers.

Filter Graph Manger 支持 IFilterGraph::EnumFilters 方法用来枚举 filter graph 中的所有 filter 。这个函数返回 IEnumFilters 接口的指针。 IEnumFilters::Next 方法返回 IBaseFilter 接口指针。

The following example shows a function that enumerates the filters in a graph and displays a message box with each filter's name. It uses the IBaseFilter::QueryFilterInfo method to retrieve the name of the filter. Note the places where the function calls Release on an interface to decrement the reference count.

下面的列子展现枚举 graph 中 filter 的方法并在一个消息框中显示每个 filter 名字。使用 IBaseFilter::QueryFilterInfo 方法获得 filter 的名字。记得调用 Release 来消耗应用计数。

HRESULT EnumFilters (IFilterGraph *pGraph) { IEnumFilters *pEnum = NULL; IBaseFilter *pFilter; ULONG cFetched; HRESULT hr = pGraph->EnumFilters(&pEnum); if (FAILED(hr)) return hr; while(pEnum->Next(1, &pFilter, &cFetched) == S_OK) { FILTER_INFO FilterInfo; hr = pFilter->QueryFilterInfo(&FilterInfo); if (FAILED(hr)) { MessageBox(NULL, TEXT("Could not get the filter info"), TEXT("Error"), MB_OK | MB_ICONERROR); continue; // Maybe the next one will work. } #ifdef UNICODE MessageBox(NULL, FilterInfo.achName, TEXT("Filter Name"), MB_OK); #else char szName[MAX_FILTER_NAME]; int cch = WideCharToMultiByte(CP_ACP, 0, FilterInfo.achName, MAX_FILTER_NAME, szName, MAX_FILTER_NAME, 0, 0); if (chh > 0) MessageBox(NULL, szName, TEXT("Filter Name"), MB_OK); #endif // The FILTER_INFO structure holds a pointer to the Filter Graph // Manager, with a reference count that must be released. if (FilterInfo.pGraph != NULL) { FilterInfo.pGraph->Release(); } pFilter->Release(); } pEnum->Release(); return S_OK; }