How to record part of the screen?

Question

   I'm using unity and easyar sdk 4

I have a second camera that is resized to part of the screen

https://imgur.com/a/Xtk7hlr

How do I record a video that is rendered on that camera?

from the EasyAR_VideoCamera prefab on RenderCamera the Target Camera is the second camera;  

right now, when i record, the result recording is stretched

https://imgur.com/a/aIx5DSh

is it possible to achieve this:

https://imgur.com/a/tBiFnYy

?

recap: https://imgur.com/a/ZUUBVZW