Take screenshot in webcam using VFrames in Console Application - delphi

Question

I'm doing a program to take a picture of the webcam using Delphi XE2 and VFrames to achieve this, the problem is that I have it all figured out, in a graphic application everything works fine, but when I use the unit in a console application, it returns me error saying
First chance exception at $76B6B727. Exception class EAccessViolation with message 'Access violation at address 004A271B in module 'console.exe'. Read of address 00000260'. Process console.exe (3676)
My Unit :
unit Webcam;
interface
uses SysUtils, Windows, Vcl.Imaging.Jpeg, Vcl.Graphics, VSample,
VFrames, Classes;
type
TWebcam = class
private
procedure NewVideoFrameEvent(Sender: TObject; Width, Height: integer;
DataPtr: pointer);
public
constructor Create;
destructor Destroy; override;
procedure capture_webcam(take_name: string);
end;
var
web_image: TVideoImage;
name_screen: string;
implementation
constructor TWebcam.Create;
begin
inherited Create;
end;
destructor TWebcam.Destroy;
begin
inherited Destroy;
end;
Procedure TWebcam.NewVideoFrameEvent(Sender: TObject; Width, Height: integer;
DataPtr: pointer);
var
bitmap: TBitmap;
name: string;
begin
name := name_screen;
if (FileExists(name)) then
begin
DeleteFile(Pchar(name));
end;
bitmap := TBitmap.Create;
bitmap.PixelFormat := pf24bit;
web_image.GetBitmap(bitmap);
bitmap.SaveToFile(name);
bitmap.Free;
web_image.VideoStop;
web_image.Free;
end;
procedure TWebcam.capture_webcam(take_name: string);
var
list_cams: TStringList;
begin
web_image := TVideoImage.Create();
list_cams := TStringList.Create;
web_image.GetListOfDevices(list_cams);
if not(list_cams.count = 0) then
begin
name_screen := take_name;
web_image.VideoStart(list_cams[0]);
end;
list_cams.Free;
web_image.OnNewVideoFrame := NewVideoFrameEvent;
end;
end.
Console :
program console;
{$APPTYPE CONSOLE}
{$R *.res}
uses
System.SysUtils,
Webcam;
var
webcamz: TWebcam;
begin
try
webcamz := TWebcam.Create();
webcamz.capture_webcam('test.jpg');
webcamz.Free();
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
end.
What should I do ?

Answer 1

The relevent source code for the VFrames unit is available on Github:
https://github.com/heise/GRBLize/blob/edge/VFrames.pas
https://github.com/heise/GRBLize/blob/edge/VSample.pas
The TVideoImage.VideoStart() method has a dependancy on Application.MainForm.Handle. A console application does not have a MainForm by default, so that alone will crash the code in a console application unless you create a MainForm (which defeats the purpose of making a console app).
Aside from that, TVideoImage also has a dependancy on a message loop, as it creates a hidden window to receive video notifications used to fire the OnNewVideoFrame event. Your console application does not have a message loop. And even if it did, you are freeing the TVideoImage object before the event would fire anyway, as your capture_webcam() code is not waiting for the event to fire before exiting.
Also, TVideoSample class (which TVideoImage uses internally) uses the DirectShow API to capture images from the webcam's video stream. DirectShow is a COM-based API. Your console application is not initializing COM before using TVideoImage. That alone would cause GetListOfDevices() to fail and return a blank list. And if you attempted to ignore that and provide a device name anyway, VideoStart() would still crash when it tries to access a COM object that TVideoSample was not able to create during construction.