# A shot contract for AI character replacement: what must stay, what may change

> Published 2026-10-19, updated 2026-10-19 · https://www.promptzone.com/lipsynclab_a357f110716ceb/a-shot-contract-for-ai-character-replacement-what-must-stay-what-may-change-138d

When you ask an AI video tool to “swap the character,” it may produce a good-looking *different* shot. That can be the wrong result. Before generating, write a short **shot contract**: what the source video must control, what the character image may change, and what variation you will tolerate.

This is a planning brief, not a magic prompt. Some tools have a prompt box; others, including the browser workflow I built, use the video and image directly. The contract helps you choose inputs and judge the result in either case.

## Copy this shot contract

```text
Goal: Replace ONE main visible subject in an authorised reference clip.

MUST KEEP from the video:
- The order and timing of the action: [describe the key beat]
- Camera position/movement and framing: [describe]
- Background and important props: [describe]
- Original audio: [keep / mute; verify that you may use it]

MAY CHANGE from the character image:
- The main subject's face, clothing and overall appearance

ACCEPTABLE VARIATION:
- Small generative differences in hair, fabric or fine background detail

FAIL IF:
- A second person changes unexpectedly
- The main gesture, camera move or shot order is rewritten
- Audio starts late, disappears, or no longer matches the visible beat
- The replacement identity drifts during a turn or occlusion
```

Fill the brackets with *observable* details. “Cinematic and consistent” is too vague to review. “The subject raises the cup at about two seconds while the camera stays locked” gives you a concrete comparison.

## A five-second example

Suppose your own clip shows one person turning toward the camera and lifting a cup. You want your original illustrated character in their place. The person, cup, background, and camera do not all have the same role:

- The **video** defines the turn, cup lift, timing, camera and room.
- The **image** defines who performs that movement.
- If the original dialogue matters, choose to keep the source sound. If not, make a silent result and add approved audio later.

Choose a reference with one clear main subject. A two-person conversation is not automatically a two-character replacement request; for a single-subject workflow, it is an ambiguous reference. Likewise, a still portrait with a radically different head angle from the visible subject makes identity harder to carry through the turn.

## Review it as an edit, not just an image

Use a simple four-point check:

1. **First frame:** Does the intended character appear in the right place and scale?
2. **Hardest moment:** Does identity survive a profile turn, motion blur, or an object crossing the face?
3. **Last frame:** Is it still the same character, with the intended action complete?
4. **Real-time playback:** Are gestures, cuts and—if retained—sound still aligned?

If the character changes but the gesture is also rewritten, choose a clearer reference beat or split a complicated edit into shorter shots. If the motion remains but the replacement identity drifts, try a sharper character image with a more compatible angle. If sound is wrong, diagnose that separately; do not assume a visual replacement tool also rewrites or repairs dialogue.

The point of the contract is to change **one variable per retry**. Otherwise, you cannot tell whether the next result improved because of the image, the clip, or the audio setting.

## Keep the scope honest

This method is best suited to an authorised short clip with one main subject. It is not a promise that every person in a crowded scene can be independently replaced, nor that a generative model will preserve every pixel. Check rights to the footage, character and soundtrack before publishing.

Disclosure: I built UseLipSync. Its Recreate workflow accepts your own **4–15 second** MP4/MOV reference and one authorised character image for a **single main subject**; it can retain the original audio when selected, and the result must be reviewed before use. The [step-by-step example with real source/output footage](https://uselipsync.com/tutorials/how-to-replace-a-person-in-a-video?source_bucket=community&campaign_code=community_promptzone) shows what this input contract looks like in practice.