DLL调用问题（高难，高手进）

Question

unit Video;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, Buttons, ExtCtrls;type
  TFrm_Video = class(TForm)
    Panel1: TPanel;
    Bit_Start: TSpeedButton;
    Bit_Stop: TSpeedButton;
    Bit_SnapShot: TSpeedButton;
    SaveDialog1: TSaveDialog;
    procedure FormCreate(Sender: TObject);
    procedure Bit_StartClick(Sender: TObject);
    procedure Bit_StopClick(Sender: TObject);
    procedure Bit_SnapShotClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;  Procedure vShowForm(h:THandle);stdcall;var
  Frm_Video: TFrm_Video;implementation{$R *.dfm}const WM_CAP_START = WM_USER;
const WM_CAP_STOP = WM_CAP_START + 68;
const WM_CAP_DRIVER_CONNECT = WM_CAP_START + 10;
const WM_CAP_DRIVER_DISCONNECT = WM_CAP_START + 11;
const WM_CAP_SAVEDIB = WM_CAP_START + 25;
const WM_CAP_GRAB_FRAME = WM_CAP_START + 60;
const WM_CAP_SEQUENCE = WM_CAP_START + 62;
const WM_CAP_FILE_SET_CAPTURE_FILEA = WM_CAP_START + 20;
const WM_CAP_SEQUENCE_NOFILE =WM_CAP_START+  63 ;
const WM_CAP_SET_OVERLAY =WM_CAP_START+  51 ;
const WM_CAP_SET_PREVIEW =WM_CAP_START+  50 ;
const WM_CAP_SET_CALLBACK_VIDEOSTREAM = WM_CAP_START +6;
const WM_CAP_SET_CALLBACK_ERROR=WM_CAP_START +2;
const WM_CAP_SET_CALLBACK_STATUSA= WM_CAP_START +3;
const WM_CAP_SET_CALLBACK_FRAME= WM_CAP_START +5;
const WM_CAP_SET_SCALE=WM_CAP_START+  53 ;
const WM_CAP_SET_PREVIEWRATE=WM_CAP_START+  52 ;
function capCreateCaptureWindowA(lpszWindowName : PCHAR;dwStyle : longint;
x : integer;
y : integer;
nWidth : integer;
nHeight : integer;
ParentWin : HWND;
nId : integer): HWND;
STDCALL EXTERNAL 'AVICAP32.DLL';Var hWndC : THandle;
    CapturingAVI : bool;Procedure vShowForm(h:THandle);stdcall;
begin
  Application.Handle := h;
  With TFrm_Video.Create(Application) Do
    Show;
end;procedure TFrm_Video.FormCreate(Sender: TObject);
begin
  CapturingAVI := false;
  hWndC := 0;
  SaveDialog1.Options := [ofHideReadOnly, ofNoChangeDir, ofPathMustExist];
end;procedure TFrm_Video.Bit_StartClick(Sender: TObject);
begin
hWndC := capCreateCaptureWindowA('My Own Capture Window',
WS_CHILD or WS_VISIBLE ,
Panel1.Left,
Panel1.Top,
Panel1.Width,
Panel1.Height,
Frm_Video.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);
Bit_Start.Enabled :=false;
end;procedure TFrm_Video.Bit_StopClick(Sender: TObject);
begin
if hWndC <> 0 then begin
SendMessage(hWndC, WM_CAP_DRIVER_DISCONNECT, 0, 0);
hWndC := 0;
Bit_Start.Enabled :=true;
end;
end;procedure TFrm_Video.Bit_SnapShotClick(Sender: TObject);
begin
if hWndC <> 0 then begin
SaveDialog1.DefaultExt := 'bmp';
SaveDialog1.Filter := 'Bitmap files (*.bmp)|*.bmp';
if SaveDialog1.Execute then
SendMessage(hWndC,
WM_CAP_SAVEDIB,
0,
longint(pchar(SaveDialog1.FileName)));
end;
end;end.
把他做成DLL然后调用。
单击"开始"按钮后报错：Access violation at address 0112D0F7 in module 'videocap.dll',Read of address 00000180.
为什么会这样，我如果不把他做成DLL的调用的时候就没有问题了。

Answer 1

With TFrm_Video.Create(Application) Do
有问题
因为DLL中的Application和程序中的对象不一致

Answer 2

http://www.ccw.com.cn/htm/app/aprog/01_2_5_5.asp看不出明顯錯誤, 先將 sendMessage 那堆東西註釋掉, 看運行如何Frm_Video.Handle 看代碼用 Panel1.Handle 似乎更對