What's the most realistic way to replace the background of a recorded falling object so it appears to be landing in different scenarios?

Appreciate your help so far. Just to chime in to answer some of the questions. The camera was on a stable tripod. I created a garbage mask around the shadow, blurred the hell out of it, and scrunched the white out with levels. I created an AI slop background for now just to see the results. It’s definitely better than it was before but still very fake. This does not need to be major motion picture level quality, but ideally better than something that looks like it was thrown together in 5 minutes. The rotoscope of the falling image isn’t perfect. There’s a lot of motion blur, which when combined with a fake background, makes it rough. The dropped object is also black which makes it hard for both the rotobrush and myself to distinguish between the shadow at the bottom and the actual object.  What settings would you recommend for the rotobrush? Would it be best to slow the footage down?

Nonetheless, I think the most difficult aspect of it all is the angle. My original idea was to turn a picture 3D to match the angle of the ground. The issue with that is that the 2D perspective in 3D looks extremely flat. Do you think it would be easier to create a 3D model of the dropped object and animate it falling in a 3D scene? 

I think Kevin is right about the best approach.  One thing I can add is that you have a nice, almost uniform background, so you should be able to:

1. take a second copy of the original 
2. add a garbage matte for the edges
3. use a transfer mode to remove the lighter parts of the image (probably Multiply)
4. Use the Levels effect to isolate the shadow
5. Drop the opacity of the layer so that the shadows match any shadows in the background plate.

Being just the shadow, a judicious bit of blurring can help and you can probably get away with the Corner Pin effect to adjust the ground plain to match the background.

Hi Jack,

Sorry you're running into this—it does sound like a challenging shot.

I don't have a VFX background, but I have a feeling it's probably more involved than just swapping the background. I wonder if a lot of it comes down to matching the new scene as closely as possible—the ground angle, perspective, lighting, and maybe recreating any shadows that help sell the landing.

If the camera is moving, it might also be worth seeing whether motion tracking or camera tracking would help, although I'm not sure how much that depends on the specific shot.

Hopefully someone with more compositing experience can chime in, but those are the first things that came to mind. I'd be interested to hear what approach you end up taking.

Thanks,
Kevin