Flux 3 Extend Video: continue the keeper, do not roll a new identity (5s, 6s, 7s, 21cr)

Use Flux 3 Extend Video only when the last frame is already a keeper. Extension spends on more seconds, not on a different idea. The catalog description: “FLUX.3 continues an existing clip beyond its final frame, generating footage consistent with the original motion and scene (source clip must be MP4, under 50 MB and under 15 seconds).” Category is extend-video. Audio is on. Video input required (video_url, max one). Credits: 21. Durations: 5s through 20s.

Flux 3 Extend Video is a continuation. If the last frame is a cousin of the product, you will get more cousins. If the last frame is the product, you will get more seconds of the product — that is the bet. Do not extend a take you would not ship. Cut or retake first. Then extend.

This is Black Forest Labs’ video key, not the Flux image roster. The hub is Black Forest Labs. The ranked list is best video extender.

MP4, under 50 MB, under 15 seconds — the source is the spec

Those three constraints are in the description. Not “any clip.” MP4. Under 50 MB. Under 15 seconds. A 40-second export will not become a legal source by optimism. Trim. Transcode to MP4 if you have to. Then extend.

Requires_image is false because the input is the clip, not a still. First-last is a different Flux 3 row: Flux 3 first last frame to video pins two stills. Extend pins a last frame you already generated or shot. Do not use extend to travel to a destination still. That is first-last. Do not use extend to invent a new scene from text. That is text-to-video.

The extend a video agent page and the extend video length task are the Versely doors. Features on this record: extend_video, continuation, native_audio, frontier, 1080p. Qualities: 720p and 1080p. Aspect ratios: 21:9, 2:1, 16:9, 4:3, 1:1, 3:4, 9:16, auto. Match the source aspect. An extend that changes 9:16 into 16:9 is a new movie.

5s is more of the same. 20s is a lot of the same.

Durations: 5s, 6s, 7s, 8s, 9s, 10s, 11s, 12s, 13s, 14s, 15s, 16s, 17s, 18s, 19s, 20s. The catalog sticker is 21 credits; the price matrix is per second. Five extra seconds of a keeper is the honest ask. Twenty extra seconds is a short film of a motion that may loop, drift, or invent a new hand. Inspect the join. The last frame of the source should be the first honest frame of the extension.

Native audio is on. The continuation will keep making sound. If the source was mute on purpose, say so or you will get a bed under a hold you meant to keep dry. If the source had a line, the extend will not reliably finish the sentence you wished you had written. Write the extra sound in the prompt for the extra seconds, or plan to replace the bed.

1080p is in the feature list and on the quality list, with 720p. There is no 4K token. A 4K delivery spec is an upscale after the extend, or a different generate. Do not extend in 720p as a “draft” if the draft is what you will concatenate.

More seconds, not a different idea

If you want a new camera, a new room, a new SKU, you want a generate. Extend will try to stay in the scene. That is the feature. Fighting it with “now we are in Paris” is how identity dies at the join. Keep the idea. Buy seconds.

21 credits is not 10 (an LTX retake) and not 70 (a Kling O3 Pro scene). Different verb. Retake replaces a stretch. Extend appends. Scene generate invents. Pick the verb that matches the last frame you actually have.

FAQ

Can I extend a 20-second source?

The description says the source clip must be under 15 seconds (and MP4, under 50 MB). Trim first. The output duration menu then runs 5s–20s of continuation.

Does this need a still?

No. It needs a video on video_url. A still-to-motion job is image-to-video or first-last, not extend.

Will it stay silent if I do not mention audio?

Audio is on. A silent prompt still gets a soundtrack you did not choose. Direct the extra seconds of sound or replace them later.

Is this the Flux image model?

No. Provider is Black Forest Labs. Flux 2 Flex is the stills family. This row is FLUX.3 video continuation at 21 credits, 5s–20s, 720p/1080p.