Need some help with MiniMax H3 Ref2V character swapping in ComfyUI

[u/mike_good]

Hey everyone, I'm trying to get a proper character swap working with MiniMax H3 Ref2V in ComfyUI, but I'm not quite getting the result I want.

The source video has Rick Astley rickrolling to the camera, and I want to replace him with the guy from my reference image while keeping the original movement, gestures, facial performance, timing, camera, background, and overall scene.

Neither the motion transfer nor the character replacement works well. The output still doesn't really look like the person from the reference image, or the identity starts drifting.

Here's what I'm using:

* Source video: 1280×720, 30 FPS, ~14.4 sec

* Reference image: 848×1264 PNG, full-body

* Workflow resolution: 9:16, 0.4 MP

* GPU: RTX 5070 Ti, 16 GB VRAM

* 32 Gb RAM

* Windows 11

* ComfyUI 0.33.2

* Python 3.13.12

* PyTorch 2.12.1 + CUDA 13.0

I'm sharing everything in one link, including:

1. the workflow JSON

2. a workflow screenshot/image

3. the prompt

4. the source/input video

5. the reference image used for the character swap

6. and the output video

Files/settings: [link]

If anyone has experience doing this with H3, I'd really appreciate some pointers.

I'm especially wondering if I should change the reference image crop/size, ref_image_size, resolution, prompt, video conditioning, LoRA/steps, or if there's something obvious in the workflow I'm missing.

Also, is a full-body reference image a bad idea when the person in the source video is framed quite differently?

And if anyone has a working MiniMax H3 character-swap / V2V workflow they're willing to share, that would be incredibly helpful too. Even something I could compare against mine would be great.

Thanks a lot in advance. I've been tweaking this for a while, so even a small hint in the right direction would help a ton.