Untitled

procedure TForm1.Button1Click(Sender: TObject);
begin
  LoadHtml(AnsiString(
    '<!DOCTYPE html>' + // we need to raise compatibility mode for the new API JavaScript
    '<html>' +
    '<head>' +
      '<meta http-equiv="X-UA-Compatible" content="IE=edge"></meta>' + // compatibility mode
    '</head>' +
    '<body>' +
      '<iframe width="560" height="315" ' + // set frame width, height
        'src="https://www.youtube.com/embed/2po4JptcOMM?' + // set source
        'autoplay=1&rel=0&controls=0&showinfo=0" ' + // autoplay, no related videos, no info nor controls
        'allow="autoplay" frameborder="0">' + // allow autoplay, no border
      '</iframe>'+
    '</body>'+
    '</html>'
  ));
end;

procedure TForm1.LoadHtml(const HTMLStr: AnsiString);
var
  aStream     : TMemoryStream;
begin
   WebBrowser1.Navigate('about:blank');//reset the webbrowser
   while WebBrowser1.ReadyState < READYSTATE_INTERACTIVE do //wait to load the empty page
   Application.ProcessMessages;

    if Assigned(WebBrowser1.Document) then
    begin
      aStream := TMemoryStream.Create;
      try
         aStream.WriteBuffer(Pointer(HTMLStr)^, Length(HTMLStr));
         aStream.Seek(0, soFromBeginning);
         (WebBrowser1.Document as IPersistStreamInit).Load(TStreamAdapter.Create(aStream));
      finally
         aStream.Free;
      end;
    end;
end;