Can not overlay a transparent Qlabel on a QWidget that Render Stream by WinID

Question

I have a Qt application that uses SDK of IP Camera to play video streams. As you may know, stream uses Qt widgets to render video frames by getting only the WinID of the Qwidget and handles the rest itself. I have a Qwidget to render video with HIKVISON SDK (IP camera SDK) and I want to overlay a transparent Qlabel on this widget but when the widget starts showing the stream, the label show the background of the widget not the stream

Here I pass WinID

  hWnd = (HWND) ui->label->winId();

Here I make label transparent

ui->label_2->setAttribute(Qt::WA_TranslucentBackground);

output:

test is label_2 and gray background is the background of label which display the video .

Any suggestions why this happens and how to avoid?