关于DsPack播放问题

在多线程中动态创建相关的VideoWindow控件，FilterGraph控件，播放一段时间后播放位置发生改变，请教一下大侠是什么原因？
本人代码如下：
  if not Assigned(FFilter[FListIndex]) then
               begin
                 FFilter[FListIndex]:=TFilterGraph.Create(APanel.pnlMain);
                 FFilter[FListIndex].AutoCreate:=False;
                 FFilter[FListIndex].GraphEdit:=False;
                 FFilter[FListIndex].Mode := gmNormal;
               end;          
               if not Assigned(FVideoWindow[FListIndex]) then
                FVideoWindow[FListIndex]:=TVideoWindow.Create(APanel.pnlMain);
                with FVideoWindow[FListIndex] do
                begin
                  visible:=False;
                  Parent:=FPanel.pnlMain;                 // OnMouseMove:=APanel.OnMouseMove;
                  BringToFront;
                  Left:=0;
                  Top:=0;                  Width:=APanel.pnlMain.Width;
                  Height:=APanel.pnlMain.Height;
                 // Align:=alClient;
                   FilterGraph:=FFilter[FListIndex];
                end;             if FFilter[FListIndex].Active then
                  FFilter[FListIndex].Active:=False;
              with FFilter[FListIndex] do
              begin
                ClearGraph;                Active:=true;
                Sleep(2);
                try
                  hr:=RenderFile(FileName);
                  if hr<>0 then
                  begin
                    Active:=False;
                    exit;
                  end;
                except
                  Exit;
                end;
             end;