TVideoImage的问题

Question

我是TvideoImage的问题，我用来从webCam中捕获图像。我有一个Timage，我使用fVideoImage.setDisplayCanvas(imgCamera.canvas)设置，第一个运行很酷，但是当我再次尝试打开时，不再有效。图像是白色的。

my code is:
on create:

       fVideoImage := TVideoImage.Create;
       bActivated := False;

       DeviceList := TStringList.Create;
       fVideoImage.GetListOfDevices(DeviceList);
       cbListaCameras.Items := DeviceList;
       DeviceList.Free;

    on power button is:

     procedure TFormCamera.btnLigarClick(Sender: TObject);
     var
       camDevice: string;
     begin
       try
          if not(bActivated)then
          begin
             camDevice := trim(cbListaCameras.Items.Strings[cbListaCameras.ItemIndex]);
             if(camDevice = '')then
             begin
                ShowMessage('Atenção, informe o dispositivo!');
                cbListaCameras.SetFocus;
                Exit;
             end;

             fVideoImage.SetDisplayCanvas(imgCamera.Canvas);
             fVideoImage.VideoStart(camDevice);
             bActivated := True;

             lblCameraStatus.Caption := 'Ligada';
             lblCameraStatus.Font.Color := clGreen;

          end
          else
             MessageDlg('Atenção, camera já está ligada!', mtWarning, [mbOK], 0);>>

       except
          bActivated := False;
          lblCameraStatus.Caption := 'Desligada';
          lblCameraStatus.Font.Color := clRed;
          ShowMessage('Atenção, erro ao tentar ligar a camera!');
       end;
    end;
    On close button is:

       fVideoImage.VideoStop;
       bActivated := false;
       imgCamera.Picture := nil;
       //imgCamera.Picture.Bitmap.Assign(nil);
       Close;

图像为白色。即使我完全免费，我也不知道，因为它发生了，请帮助我。