Hello,
You have to create two sections.
One with your video, one with your image.
Set your Hero for mobile to display none on desktop.
Then go to Tablet tab, and set your hero mobile to display.
From there, your hero mobile won’t display on desktop but will display for ipad and lower.
Now just display none the section with your video on tablet tab
And threre you have it !
Note that in my example i used a GIF which is nice to replace video sometimes for devices.