Image Replace - not a rectangle

I do a lot of real estate tour videos using a Ronin and Mocha has been AWESOME at adding a crackling fire in an empty fireplace.

Does anyone have a tip on how to do a similar effect when the replacement area isn’t a rectangle like a TV screen or fireplace?

Specifically for me today, it’s an octagonal hot tub that’s sunken into an deck that was empty and full of dirt and spiders.


Make a plane for the water and then create a roto mask that’s an octagon to trim it neatly into the space. Or comp by walls, making each wall you can see a plane. Water is hard without a proper simulation, but you can probably cheat something.

Thanks Mary.

Let’s say I have video of water in a hot tub. Thta’s what I want to composite “over” the moving video of the empty hot tub. Using your first suggestion, how does the footage of the water track the movement of the foreground? Doesn’t your technique just cut a hole in the top of the tub? and how do I do that composite? I’m quite new at Mocha.

I thought about doing a camera track and putting the water in place in 3d space and not having to mask the tub.

You’d essentially be doing a corner pin track and matching a similarly angled composite and using rotoscoping to shape the water. It would be an imperfect solution. A 3D solution is better, but you’d need to do either a mocha camera solver and place a null for the hot tub, OR do a non-mocha camera solve for the entire scene and use Mocha rotoscoping to blend your 3D render and your plate. In the 3D scenario, you need to make a similar model to the hot tub to match the motion and constrain your water simulation.