Black screen before HMI is rendered for the first time

[AdarshKale]

Hello Qt Experts!!!
We have a situation as described below.

We have a Welcome animation rendered on the embedded system, and immediately once the animation is complete, HMI is rendered on the Display.
we are seeing a second of black screen rendered on the display between the switch in Animation and HMI.
The animation is a video rendered in a different pipeline from the platform (Non QT)

As an experiment we tried as below.
In the very first QML which gets called, we added a simple rectangle of color green and added a trace in onCompleted of that Ractangle component.
we could see that the oncompleted is called even when the animation is in its last frames. which ensures, the QML is ready to be rendered.

We have pipeline where the animation is lower priority than HMI.
Can you please suggest where could this black screen being rendered?