Coder needed.

[Darwinian]

Whoa, Who'd have thought it would be this simple?

Code:

procedure TForm1.RegisterFileType(ExtName:String);
var
  a: byte;

begin
  a:=0;

  with TRegistry.Create do
  try
    RootKey := HKEY_CLASSES_ROOT;

    DeleteKey('\.avi\');

    if OpenKey('\.avi\', True) then begin
      WriteString('','avifile');
      WriteString('PerceivedType', 'video');
      WriteString('Content Type', 'video/avi');
    end;

    OpenKey('\.avi\OpenWithList\ehshell.exe\', True);

    if OpenKey('\.avi\OpenWithProgIds\', True) then
      WriteBinaryData('avifile', a, 1);

   if OpenKey('\avifile\shell\open\command\', True) then
      WriteString('', '"'+ParamStr(0)+'" "%1"');

    RootKey := HKEY_CURRENT_USER;

    DeleteKey('\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.avi\');

    if OpenKey('\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.avi\OpenWithProgids\', True) then
      WriteBinaryData('avifile', a, 1);

  finally
    Free;
  end;

  SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, 0, 0);
end;