Continue work on a webcam / app project

I have a project here done in Angular and nodeJS that is like 95 % done.
Unfortunately, the developer was not capable to deliver the last requirement.

What I currently have and is working

The app that runs on a portrait screen:
- two window section
- Upper part shows webcam image
- Lower part shows a video in an endless loop
- possibility to move the border
- (whole environment stuff like selecting different webcams, restarting with same setting as last use, loading of video, loop play etc)

The only problem is that the content of the two windows does not scale neatly and behave as it should

I want:
- Content of upper window to be bottom & center-aligned when resized
- Content of lower window to be top & center-aligned when resized

Depending on "Keep aspect ratio" checkbox this will be achieved by distorting the images or by zooming in and out to fill the space.

So that the content of the windows is always touching in the middle.

Please see the attached PDF for reference.
All is working the issue is only the resizing part.

Complete source code of current state is provided by me.

I have a strong feeling that the person who coded it just did not understand that requirement.
For an expert should be quite easy to fix. Please only bid if you understood the problem here.