I got the video feed on the H12 in the HEQ app that is preinstalled, and the Skydroid version of Tower.
The video feed is over some USB system hooked up internally, and requires UVC support.
QGC is not a native android app, and uses QT. QT has limited support for UVC. So it either appears as a source option or not.
One suggestion, that I have not tired is a native app that supports UVC and sends out as RTSP - Any chance of UVC video support?