使用AVICAP32.DLL来捕获摄像头的图像并保存到数据中,捕完后怎么关闭那个黑块的窗体呀?

procedure TForm1.OpenVideoClick(Sender: TObject);
begin
hWndC := capCreateCaptureWindowA('My Own Capture Window',
WS_CHILD or WS_VISIBLE ,
Panel1.Left,
Panel1.Top,
Panel1.Width,
Panel1.Height,
Form1.Handle,
0);
if hWndC <> 0 then
SendMessage(hWndC, WM_CAP_SET_CALLBACK_VIDEOSTREAM, 0, 0);
SendMessage(hWndC, WM_CAP_SET_CALLBACK_ERROR, 0, 0);
SendMessage(hWndC, WM_CAP_SET_CALLBACK_STATUSA, 0, 0);
SendMessage(hWndC, WM_CAP_DRIVER_CONNECT, 0, 0);
SendMessage(hWndC, WM_CAP_SET_SCALE, 1, 0);
SendMessage(hWndC, WM_CAP_SET_PREVIEWRATE, 66, 0);
//SendMessage(hWndC, WM_CAP_SEQUENCE_NOFILE, 1, 0);
SendMessage(hWndC, WM_CAP_SET_OVERLAY, 1, 0);
SendMessage(hWndC, WM_CAP_SET_PREVIEW, 1, 0);
OpenVideo.Enabled :=false;
end;

procedure TForm1.CloseVideoClick(Sender: TObject);
begin
if hWndC <> 0 then begin
SendMessage(hWndC, WM_CAP_DRIVER_DISCONNECT, 0, 0);
hWndC := 0;
OpenVideo.Enabled :=true;
end;
end;