How prompt-based replacement differs from keying
Chroma keying cuts the subject out and layers it over a plate; every keying artifact you've seen — green fringes, buzzing hair edges, mismatched light — comes from that cut-and-paste. A generative swap re-renders the whole frame coherently: the new environment casts its light on the subject, the subject occludes the background correctly, and edges are drawn, not matted.
The honest trade: a re-render means the output is a new take, not your original pixels with a new layer behind them. Faces, products, and fine details almost always carry through faithfully — but check them the way you'd check any generated shot, and rerun if something drifted.
Getting a clean swap
Clear subject-background separation is the biggest predictor of success: a person or product that reads distinctly against the original backdrop swaps cleanly. Describe the lighting along with the place — 'a golden-hour rooftop, warm light from camera left' — so the subject is re-lit consistently instead of pasted into a scene whose light doesn't match.
Trickier cases, stated plainly: hair blowing against busy backgrounds, reflective and transparent objects that carry the old environment in their surfaces, and subjects physically leaning on the wall you're replacing. These can work, but expect more variation between takes.
What people use it for
Talking clips get relocated from spare rooms to branded sets. Product demos shot on a kitchen counter move to a lifestyle scene or a clean studio sweep. UGC-style clips get a consistent backdrop across a whole campaign, so a batch shot in five different places reads like one shoot.
For still images, Nidhogg's dedicated background remover gives you a proper transparent cutout — the right tool when you need a layered asset rather than a finished frame. For video, describe the destination and let the re-render do the compositing.
A workflow that holds up
One environment per pass, described concretely: place, time of day, light direction, mood. Append 'keep the subject, framing, and motion unchanged' — it meaningfully improves fidelity to your original take. For an important swap, generate two or three versions and keep the strongest.
Then finish: run the winning clip through the video upscaler for delivery resolution, and use reframe if the new placement needs a different aspect ratio than your master.