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SCAIL-2 in-video character replacement on WAN 2.1 — WanSCAILToVideo + SCAIL2ColoredMask + SAM3, the reference-image framing→scale rule, and the tuning/compositing pitfalls
Passed 23 of 24 test cases with the skill, and 9 of 24 without it.
and 16 more in the full report
14 fixed9 passed either way1 still failing0 broke
Tokens, turns and time describe resource use, not a dollar price.
One of 14 test cases the skill fixed. Same model, same prompt, with and without the skill.
Which specific segment-anything model checkpoint is used in the official SCAIL-2 ComfyUI template for driven character masking?
| Checked | Without skill | With skill |
|---|---|---|
| identifies sam3.1_multiplex_fp16 as the mask model | Missed | Passed |
The instructions your model reads when the skill loads.
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.
In replacement_mode: true, the reference image's FRAMING controls the output
character's SIZE as well as 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 the same height). Pose transfer was correct in both cases. Only the scale was wrong, which makes it easy to misread as "the model works" until you A/B against the source.
Guidance: pad or reframe the reference before you render.
Pad/reframe the reference image onto a canvas at the working resolution so the person occupies roughly the same fraction of frame height as the subject in the driving video. A full-bleed portrait reference against a wide-shot driving clip renders the character oversized in proportion to the framing mismatch.
test cases passed, vs 9 / 24 without
More skills from the same source and nearby in the registry, with their headline benchmark lift.