DirectShow Editing Services - problem with MS example

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

passpicsAsked:
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

x
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Lee_NoverCommented:
do NOT use _Release !!! instead set the interfaces to nil !
0
gmayoCommented:
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

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
passpicsAuthor Commented:
Thanks! I assume C++ works differently then. Or are MS giving out flunky examples?
0
gmayoCommented:
It's the way Borland chose to handle interfaces. Whether that is right or wrong is open to some debate!

Cheers

Geoff M.
0
Lee_NoverCommented:
and I like it this way better :)
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Delphi

From novice to tech pro — start learning today.