Give it a clip under 15 s and one change; get the clip back re-rendered with that
detail gone and everything else in place. It fixed a mustache that a recast carried
over, where re-prompting the recast could not. To swap the person, use h3-max-recast;
to fix a still before animating, edit the frame instead (guide-edit-a-frame-before-animating).
Inputs
- The clip: MP4, under 15 s and under 50 MB. Billed per second of input.
- One change, with the person it applies to named by what the frame shows.
- No on-screen text in the clip: lyrics, titles, captions (Tips and traps).
Run it
Call describe("fal/blackforestlabs/flux-3/edit-video") before the first run in a job,
then:
run("fal/blackforestlabs/flux-3/edit-video", {
"video_url": "<job>/recast/raw/partA_recast_b.mp4",
"prompt": "<the change, then what stays; see below>"
}, into="<job>/recast/raw", unit="partA_shave", tag="partA")
There is no seed, size or resolution field; safety_tolerance (0 to 4, default 2) was
left alone.
Prompt
The change in one sentence, stated as the result in every frame, then "Change nothing else" and the list of what stays:
Remove the mustache from the man on the left in the dark jacket: he is completely clean-shaven, with a smooth bare upper lip, in every frame. Change nothing else: keep both faces, expressions, mouth movements, hair, clothes, every movement and its timing, the title card, the set, the light and the camera.
What you get
An MP4 of the same length and timing at about 1248×704 (16:9 in), with the change made. The motion and mouth movements matched the input frame for frame.
Tips and traps
- It rewrites on-screen text: on a clip with handwritten lyrics it invented new lines, even with "keep the lyric text" in the prompt. Use it only on clips without text, or splice the text frames back from the input.
- The size drops: upscale back to the delivery size with Lanczos and a light unsharp
(
python-conform-to-1080pcovers the scale) before splicing. - Cheaper than the alternatives tried for the same mustache: Kling v4 video-to-video edit left it in and cost $2.80 for 9 s; Gemini Omni Flash edit refused the clip.
Check it
- Measure the output's size and length (
ffprobe-inspect-media). - Compare a frame sheet every 0.75 s with the input's: the detail gone in every frame, faces and mouths unchanged, every text frame identical.
- Put it to the person with
review_approve, the input asoriginal.
