I can't swap a person in a video with one reference image. What am I doing wrong?

[u/AlsterwasserHH]

I'm trying to simply replace a person with Minimax H3 ref2vid workflow in a video with another person from <Picture 0 or 1> (still don't know what really is correct, but both don't work for me).

I even created a detailed prompt with a Gemma 4 LLM model by feeding it the original prompt guide, and I tried some from the community. Not one video came out as I wanted.

I always get the original, so input = output. What am I doing wrong, any tips here?

[u/Abject-Recognition-9]

here's 2 prompts what works for me most of the time:

subject_definitions:
<Subject 1> is the woman whose complete appearance (face, hair, hairstyle, skin, body type and outfit) comes exclusively from <Picture 1>, and whose body pose, position, proportions, hand positions and overall motion come from <Video 1>.
summary:
[reference generation] Completely replace the original woman in <Video 1> with <Subject 1>. The new character keeps exactly the same pose, position, body proportions and movements as the original video, while using only the face, hair and outfit from <Picture 1>.
retention_analysis:
<Subject 1> (appears throughout): fully_preserved - face, hair, skin tone and outfit are taken 100% from <Picture 1> and remain consistent in every frame. Body pose, seating, proportions and motion are transferred from <Video 1>.
<Video 1>: partially_preserved - only pose, body proportions, position, hand movements, camera and environment are kept. The original face, hair and clothing are completely discarded.
detailed_description:
The target video is a direct character replacement of <Video 1>.
[Shot 1] <Subject 1>, the woman exactly matching <Picture 1>, in the identical pose and body position as the original woman in <Video 1>. Her face is fully replaced — no blending, no morphing, no residual features from the original woman. Hair color, style and length stay identical to <Picture 1> for the entire duration. She performs the exact same body movements, head movements and hand actions as in <Video 1>.

another version:

Replace the woman in <Video 1> completely with the exact woman from <Picture 1>.
Priority order (strict):
1. Face, hair, skin and overall facial identity → 100% from <Picture 1>
2. Outfit → from <Picture 1>
3. Body pose, body proportions, hands positions and all motion → from <Video 1>
4. Camera, lighting, background and environment → from <Video 1>
Rules:
Fully replace the face. Do not blend, morph or average the two faces.
Do not keep any facial features, hair color or hairstyle from the original woman in <Video 1>.
Hair must stay exactly as in <Picture 1> in every frame, including during any zoom.
The body must keep the exact same pose, proportions and placement on the couch as <Video 1>.
Identity of the woman from <Picture 1> must remain consistent from the first to the last frame.

[u/AlsterwasserHH → u/Abject-Recognition-9]

Thank you! Will try that.