{"id":511,"date":"2008-08-06T22:44:36","date_gmt":"2008-08-06T20:44:36","guid":{"rendered":"https:\/\/alax.info\/blog\/?p=511"},"modified":"2008-08-09T08:23:41","modified_gmt":"2008-08-09T06:23:41","slug":"how-to-wrap-an-existing-directshow-filter-with-a-private-video-source-filter","status":"publish","type":"post","link":"https:\/\/alax.info\/blog\/511","title":{"rendered":"How To: Wrap an existing DirectShow filter with a private video source filter (COM aggregation)"},"content":{"rendered":"

See beginning in microsoft.public.win32.programmer.directx.video<\/a> newsgroup.<\/p>\n

This sample is demonstrating COM aggregation<\/a> to embed an existing filter an re-expose it as a new filter having inner filter pre-initialized.<\/p>\n

The Visual Studio C++.NET 2008 projects contains a DirectShow<\/a> filter class that registers itself under Video Capture Sources category<\/a> and embeds File Source (Async) Filter<\/a> inside initialized to stream clock.avi<\/em> file from Windows directory.<\/p>\n

\"\"<\/a><\/p>\n

<\/p>\n

\"\"<\/a><\/p>\n

The code of interest is in Filter.h<\/em>. CFilter<\/em> class is the implementation of the DirectShow filter.<\/p>\n

CFilter<\/em> registers itself as a filter through static UpdateRegistry<\/em> method, which overrides stock DECLARE_REGISTRY_RESOURCEID<\/a> macro and adds IFilterMapper2 interface calls to register\/unregister the filter.<\/p>\n

To take an advantage of aggregating another object we need DECLARE_PROTECT_FINAL_CONSTRUCT<\/a> macro to be able to instantiate inner (that is aggregated) object on the very start (we cannot do this right in constructor), DECLARE_GET_CONTROLLING_UNKNOWN<\/a> macro to declare member menthod that exposes controlling unknown.<\/p>\n

In a FinalConstruct<\/a> method we instantiate aggregated object (note GetControllingUnknown() argument which indicates instantiating as aggregated):<\/p>\n

ATLENSURE_SUCCEEDED(m_pInnerUnknown.CoCreateInstance(CLSID_AsyncReader, GetControllingUnknown()));<\/pre>\n
and initialize the object through IFileSourceFilter::Load<\/a>. The inner object is ready and we are to expose its functionality as if implemented natively. We need to update object’s COM MAP<\/a> for this:<\/p>\n
BEGIN_COM_MAP(CFilter)\r\n\tCOM_INTERFACE_ENTRY(IFilter)\r\n\t\/\/ NOTE: We still implement IDispatch through IFilter but we hide it to hopefully expose inner filter's IDispatch\r\n\t\/\/COM_INTERFACE_ENTRY(IDispatch)\r\n\t\/\/ NOTE: We are hiding inner filter IFileSourceFilter to avoid GraphEdit prompts for file path on filter insertion\r\n\tCOM_INTERFACE_ENTRY_NOINTERFACE(IFileSourceFilter)\r\n\tCOM_INTERFACE_ENTRY_AGGREGATE_BLIND(m_pInnerUnknown)\r\nEND_COM_MAP()<\/pre>\n
COM_INTERFACE_ENTRY_AGGREGATE_BLIND<\/a> will expose all inner object interfaces (except mentioned higher on the map) to the outside world. And we explicitly suppress IFileSourceFilter<\/a> through COM_INTERFACE_ENTRY_NOINTERFACE<\/a> to prevent GraphEdit<\/a> from discovering it and popping up a file dialog to select a source file.<\/p>\n
Source code: DirectShowWrapperSourceFilterSample.01.zip<\/a> (note that Release build binary is included)<\/p>\n","protected":false},"excerpt":{"rendered":"
See beginning in microsoft.public.win32.programmer.directx.video newsgroup. This sample is demonstrating COM aggregation to embed an existing filter an re-expose it as a new filter having inner filter pre-initialized. The Visual Studio C++.NET 2008 projects contains a DirectShow filter class that registers itself under Video Capture Sources category and embeds File Source (Async) Filter inside initialized to… <\/p>\n
Read the full article<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11,13,10],"tags":[96,487,97,95,78,94,488,486],"class_list":["post-511","post","type-post","status-publish","format-standard","hentry","category-atl","category-source","category-video","tag-aggregation","tag-atl","tag-avi","tag-com","tag-directshow","tag-hack","tag-source","tag-video"],"_links":{"self":[{"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/posts\/511","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/comments?post=511"}],"version-history":[{"count":0,"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/posts\/511\/revisions"}],"wp:attachment":[{"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/media?parent=511"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/categories?post=511"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/tags?post=511"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}