有关双摄像头的编程问题,急... ,在线等待

我的电脑有2个摄像头,我要在一个程序里面去同时使用2个摄像头,
但是当我使用SendMessage (hWndC, WM_CAP_DRIVER_CONNECT, 1, 0)的使用,却不能成功的连接第2个摄像头.
我的原代码是:
hWndC1 := capCreateCaptureWindowA('My Own Capture Window',
                                        WS_CHILD or WS_VISIBLE ,
                                        Panel3.Left,
                                        Panel3.Top,
                                        Panel3.Width,
                                        Panel3.Height,
                                        Form1.Handle,
                                        0);
  if hWndC1 <> 0 then
    SendMessage(hWndC1, WM_CAP_SET_CALLBACK_VIDEOSTREAM, 0, 0);
  SendMessage(hWndC1, WM_CAP_SET_CALLBACK_ERROR, 0, 0);
  SendMessage(hWndC1, WM_CAP_SET_CALLBACK_STATUSA, 0, 0);
  SendMessage(hWndC1, WM_CAP_DRIVER_CONNECT, 1, 0);
  SendMessage(hWndC1, WM_CAP_SET_SCALE, 1, 0);
  SendMessage(hWndC1, WM_CAP_SET_PREVIEWRATE, 66, 0);
  SendMessage(hWndC1, WM_CAP_SET_OVERLAY, 1, 0);
  SendMessage(hWndC1, WM_CAP_SET_PREVIEW, 1, 0);