Bria Video Replace Background

Bria Video Replace Background is the "I shot this in my living room, make it look like I didn't" node. You give it a foreground video plus a background - either a still image or another video - and Bria separates the subject and composites it over your new backdrop, keeping the foreground's resolution and frame rate. One call, and the finished composite comes back. It's the most useful of the three Bria background nodes precisely because it's the only one that goes all the way to a final shot instead of stopping at a mask or a green screen.

It's a built-in partner node: the compositing happens in the cloud through Comfy's API and you're billed per second, with no local model or GPU involved. The KB's background-removal essay is the right context here - local removers are great on single images, but video needs the temporal stability an API like Bria is built for, and this node layers the compositing on top so you don't stitch it yourself.

The inputs

• video - the foreground clip whose background is replaced. Capped at 60 seconds before billing.
• background_image or background_video - the new backdrop. Provide one or the other, never both; the tooltip is explicit, and the node enforces it.
  • An image gives you a static backdrop - perfect when you've generated a location still.
  • A video gives you a moving backdrop - the classy way to composite a subject into an AI-generated scene that has motion.
• seed - re-run control only; results are nondeterministic regardless of seed.

What comes out

A single VIDEO output: your foreground composited over the supplied background, at the foreground's original resolution and frame rate.

Gotchas

• Aspect ratio mismatch = distortion. The node description warns directly: a background with a different aspect ratio is stretched to fit, so your beach backdrop will look wrong on a portrait subject clip unless you match the ratio first. Resize/crop the background before you send it.
• Both-or-neither on backgrounds. Supplying both image and video is a validation error. Pick one.
• It's a paid call per second, and foreground quality gates the result. A messy subject separation makes the composite look pasted; clean lighting on the foreground does most of the work.
• Seed is a re-run key, not a lock. Same disclaimer as every node in this family.

The pattern people actually run: generate a subject locally → record it (or generate a clip) → this node with a generated background image → a finished, location-looking shot with zero manual keying. The green-screen node is for editors who want to key later; this one is for people who want the shot now.