wan-scail-replacement

# SCAIL-2 In-Video Character Replacement (WAN 2.1) SCAIL-2 (zai-org, on WAN 2.1 14B) replaces the person in a driving video with a character you supply as a reference image — end-to-end, with no pose maps, and with multi-character support. It is the successor to WAN Animate / motion transfer for the "swap the subject, keep the motion" job. The official ComfyUI template is **`video_wan21_scail2_character_replacement_int8`**, built around `WanSCAILToVideo` (+ `SCAIL2ColoredMask`) with a SAM3 mask driving *where* the character goes. This skill documents the non-obvious behaviours that cost a full multi-minute render to discover. It is not a from-scratch graph — start from the official template and apply the guidance below. ## The one rule that costs a re-render: reference framing controls SCALE **In `replacement_mode: true`, the reference image's FRAMING controls the output character's SIZE — not just its appearance.** The SAM3 mask controls *where* the character is placed; the reference image controls *how large*. Measured on a 720x1280 driving clip where the subject occupied ~30% of frame height (subject bbox 363 px): | Reference framing | Person bbox in output | vs driving subject | |---|---|---| | Full-bleed portrait (person ~93% of frame) | 621 px | **1.71x oversized** | | Reframed (person ~34% of frame) | 364 px | **1.003x — correct** | After reframing, top/bottom registration matched the driving subject within 1 px (the character stands on the same ground plane at ...