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DirectShow Editing Services - problem with MS example

Posted on 2003-12-12
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Last Modified: 2008-02-07
I've tried converting the MS Directshow Editing services demo (on the MS developers web site) to Delphi, using the Directshow9.pas header provided by JEDI at www.prodigy.com. Everything works fine except I get an exception whenever I use a _release statement. My code is as follows:

procedure TForm1.PreviewTL(pTL : IAMTimeline; pRender : IRenderEngine);
var
    pGraph : IGraphBuilder;
    pControl : IMediaControl;
    pEvent : IMediaEvent;
    evCode : integer;
begin
     // Preview a timeline.
     // Build the graph.

     pRender.SetTimelineObject(pTL);
     pRender.ConnectFrontEnd();
     pRender.RenderOutputPins();

     // Run the graph.
     pRender.GetFilterGraph(pGraph);
     pGraph.QueryInterface(IID_IMediaControl,pControl);
     pGraph.QueryInterface(IID_IMediaEvent,pEvent);
     pControl.Run();

     pEvent.WaitForCompletion(INFINITE, evCode);
     pControl.Stop();

     // Clean up.
     //pEvent._Release();
     //pControl._Release();
     //pGraph._Release();
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  pTL : IAMTimeline;  //The main timeline
  pGroup: IAMTimelineGroup;
  pGroupObj: IAMTimelineObj;
  mtGroup: AM_MEDIA_TYPE;
  pTrackObj: IAMTimelineObj;
  pTrack: IAMTimelineTrack;
  pComp: IAMTimelineComp;
  pSource: IAMTimelineSrc;
  pSourceObj: IAMTimelineObj;
  bstrFile: String;
  pRenderEngine: IRenderEngine;
  hr : integer;

begin
     bstrFile := 'C:\cvr\goodtime.avi';
     QzInitialize(nil);
     QzCreateFilterObject(CLSID_AMTimeline, NIL, CLSCTX_INPROC_SERVER,
         IID_IAMTimeline, pTL);

     //Add a video group to the timeline.

     hr := pTL.CreateEmptyNode(pGroupObj,TIMELINE_MAJOR_TYPE_GROUP);
     Showmessage(inttostr(hr));
     pGroupObj.QueryInterface(IID_IAMTimelineGroup,pGroup);

     (* Set the group media type. This example sets the type to "video" and*)
     (* lets DES pick the default settings. For a more detailed example,*)
     (* see "Setting the Group Media Type."*)

     ZeroMemory(@mtGroup,sizeof(AM_MEDIA_TYPE));
     mtGroup.majortype:= MEDIATYPE_Video;
     pGroup.SetMediaType(@mtGroup);
     pTL.AddGroup(pGroupObj);
     //pGroupObj._Release();

     (* TRACK: Add a track to the group.*)
     pTL.CreateEmptyNode(pTrackObj,TIMELINE_MAJOR_TYPE_TRACK);
     pGroup.QueryInterface(IID_IAMTimelineComp,pComp);
     pComp.VTrackInsBefore(pTrackObj,0);
     pTrackObj.QueryInterface(IID_IAMTimelineTrack,pTrack);

     //pTrackObj._Release();
     //pComp._Release();
     //pGroup._Release();

     (* SOURCE: Add a source to the track.*)
     pTL.CreateEmptyNode(pSourceObj,TIMELINE_MAJOR_TYPE_SOURCE);
     pSourceObj.QueryInterface(IID_IAMTimelineSrc,pSource);
     pSourceObj.SetStartStop(0,60000000);

     (* Set the times and the file name.*)
     pSource.SetMediaName(bstrFile);
     pSource.SetMediaTimes(10000000,70000000);
     pTrack.SrcAdd(pSourceObj);
//     SysFreeString(bstrFile);
     //pSourceObj._Release();
     //pSource._Release();
     //pTrack._Release();

     (* Preview the timeline.*)
     CoCreateInstance(CLSID_RenderEngine,nil,CLSCTX_INPROC_SERVER,IID_IRenderEngine,pRenderEngine);
          PreviewTL(pTL,pRenderEngine);
     pRenderEngine.ScrapIt();
     (* Clean up.*)
     //pRenderEngine._Release();
     //pTL._Release();
     CoUninitialize();

end;


As you see I've removed all the _Release statement, and things work fine (except that's not a good idea...). Any ideas as to what might be wrong? Anyone else working with Editing Services I can talk this through with?

Cheers!

Martin Coster

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Question by:passpics
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5 Comments
 
LVL 12

Assisted Solution

by:Lee_Nover
Lee_Nover earned 300 total points
ID: 9928192
do NOT use _Release !!! instead set the interfaces to nil !
0
 
LVL 8

Accepted Solution

by:
gmayo earned 450 total points
ID: 9928408
All you need do is:
pRenderEngine := nil;

Strange as it may sound, that's all you need do. Any variable you assign to an interface will increment its reference count. Any setting of a variable that is an interface will effectively call _Release, hence the need to not do it.

Geoff M.
0
 

Author Comment

by:passpics
ID: 9932720
Thanks! I assume C++ works differently then. Or are MS giving out flunky examples?
0
 
LVL 8

Expert Comment

by:gmayo
ID: 9933782
It's the way Borland chose to handle interfaces. Whether that is right or wrong is open to some debate!

Cheers

Geoff M.
0
 
LVL 12

Expert Comment

by:Lee_Nover
ID: 9933922
and I like it this way better :)
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