Body Double: recast the performer in a take with open weights in ComfyUI

What it is. Body Double, by Luis Catacora (@lucataco), recasts the performer in a video as a new character and keeps everything else in the shot. It runs on stock ComfyUI core nodes with open-weights models only (SAM 3.1, FLUX 3 Image Klein and SCAIL-2) and is pitched as an open alternative to Higgsfield's Genjutsu. His submission post, made late on Oct 29 MDT, passed 590 likes and 400 bookmarks overnight, and Comfy CEO Yoland Yan replied "Holy shit, this is so good!" On Oct 30 lucataco said he'd updated the workflow to FLUX 3. Apache-2.0.

How it works. SAM 3.1 finds and tracks the performer, re-identifying them by appearance after turns, occlusions or hard cuts. A smoothed virtual follow-cam keeps them large at the model's resolution, because, per the README, SCAIL-2 does badly on small figures. FLUX 3 Image Klein paints the new character into the first frame (you pick one of four options) and that frame anchors identity. SCAIL-2 then renders 81-frame segments, each conditioned on the last five frames of the one before, with a QC check for seams and background drift that re-rolls a flagged segment. Only the recast performer is pasted back into the untouched full-resolution plate, so the set, crowd and grain stay as shot. Runs resume after a crash.

What it needs. About 50 GB of GPU memory for the segments and about 42 GB of disk for models, plus a Hugging Face account that has accepted the gated FLUX 3 Image Klein licence and acceptance of Meta's SAM licence. Per the creator's table, the 30 s, 1080p demo took about 100 minutes on a DGX Spark and 48 minutes on an H100 PCIe 80 GB. Tested on those two machines; there's an optional relight LoRA so the cast picks up the scene's light, and a check that stops a run if the cast image holds a prop the performer doesn't.

Use it responsibly. This is a tool for recasting performers you have the rights to, for example your own talent shot for a client, or a stock clip whose licence allows it, as in the creator's demo. Don't use it to put a real person's likeness on someone else's body without their consent.

Our take: the design choice that matters is the composite. Most character-swap tools re-render the whole frame, which is why backgrounds swim; Body Double only replaces the person and keeps the plate, which is what a production would ask for. The 50 GB requirement means a rented H100 for most teams, so treat it as a pipeline to study and run on cloud GPUs, not a laptop tool.