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FLUX 3 Video Extend

black-forest-labs/

FLUX 3 Video Extend continues input videos into new 5-20 second clips, using prompt guidance to control the next action, camera movement, visual style, motion continuity, and optional synchronized audio at 720P / 1080P output. Ready-to-use REST inference API, best performance, no coldstarts, affordable pricing.

video-extend
Input

Idle

$0.85per run·~11 / $10

ExamplesView all

Continue directly as the dinosaur skeleton begins moving. It carefully steps down from the exhibition platform, sending small bones and dust across the floor. The paleontologist runs through the gallery while other fossil displays begin moving behind glass cases. The camera tracks beside her, then swings around as she reaches the museum entrance and finds a living prehistoric jungle outside instead of the city. Maintain the same character, clothing, museum layout, lighting, and movement continuity.

Related Models

README

FLUX 3 - Video Extend

FLUX 3 Video Extend continues a required input video into a new clip guided by your prompt. Describe what should happen next, how the camera should move, and how the visual style or atmosphere should continue to create a smooth extension with optional synchronized audio.

Key Capabilities

  • Continue an existing video with prompt-guided action and scene development.
  • Extend the visual flow while maintaining the source video's subject, environment, and overall style.
  • Generate optional synchronized audio for the extended section.
  • Choose 720p or 1080p output and a duration from 5 to 20 seconds.
  • Support common landscape, portrait, square, and cinematic aspect ratios.

Parameters

ParameterRequiredDescription
promptYesDescribe the action, scene development, camera movement, mood, lighting, and visual continuity for the extension.
videoYesInput MP4 video used as the starting point. The source must be under 50 MB and under 15 seconds.
aspect_ratioNoOutput aspect ratio. Options: 21:9, 2:1, 16:9, 4:3, 1:1, 3:4, or 9:16.
resolutionNoOutput resolution. Options: 720p or 1080p. Default: 720p.
durationNoDuration of the generated extension in seconds. Choose an integer from 5 to 20. Default: 5.
generate_audioNoGenerate synchronized audio for the extended video. Default: true.

How to Use

  1. Upload an MP4 source video that is under 50 MB and under 15 seconds.
  2. Describe the next event or movement in the prompt, including how the scene, camera, and subject should continue.
  3. Choose the output aspect ratio, resolution, and extension duration.
  4. Enable generate_audio when the continuation should include matching ambience, effects, music, or dialogue.
  5. Submit the request and download the extended video after processing is complete.

Prompting Tips

  • Begin the prompt with the next action rather than repeating the entire source video.
  • Refer to continuity explicitly: continue the camera movement, keep the same lighting, preserve the character's appearance, or maintain the same environment.
  • Use a clear transition point and describe the first visible action after the source video ends.
  • Mention any desired change in camera direction, pacing, mood, or sound.

Pricing

Pricing is calculated by billed video duration and output resolution.

ResolutionPrice
720p$0.17/s
1080p$0.29/s

Billing Rules

  • The billed duration is rounded up to the next whole second.
  • The minimum billed duration is 5 seconds.
  • The maximum billed duration is 20 seconds.
  • Audio generation does not add a separate charge in the current pricing formula.
  • Example: a 10-second 720p video costs $1.70.
  • Example: a 10-second 1080p video costs $2.90.

Best Use Cases

  • Extending short clips into longer story beats.
  • Continuing product demonstrations, character actions, and camera moves.
  • Creating smooth transitions for social videos, advertisements, and trailers.
  • Exploring alternate endings or next-scene concepts from existing footage.

Notes

  • An input video and prompt are both required.
  • The source video must be MP4, under 50 MB, and under 15 seconds.
  • Results depend on the visual continuity and motion cues present in the source video and prompt.

Related Models

Note:This website uses AI models provided by third parties.

Flux 3 Video Extend API — Quick start

Grab a WaveSpeedAI API key, then call POST https://api.wavespeed.ai/api/v3/black-forest-labs/flux-3/video-extend with your input as JSON. The endpoint returns a prediction id. Start polling the result endpoint around every 2 seconds, increase the interval for long-running tasks, and stop on any terminal status. On completed, read output values from data.outputs. Examples for Flux 3 Video Extend below.

HTTP example
set -euo pipefail

: "${WAVESPEED_API_KEY:?Set WAVESPEED_API_KEY}"

REQUEST_BODY=$(cat <<'JSON'
{
    "prompt": "A cinematic shot of a city at sunset, soft golden light",
    "video": "https://interactive-examples.mdn.mozilla.net/media/cc0-videos/flower.mp4",
    "aspect_ratio": "21:9",
    "resolution": "720p",
    "duration": 5,
    "generate_audio": true
}
JSON
)

# 1. Submit the prediction.
SUBMIT_RESPONSE=$(curl --silent --show-error --fail-with-body \
  -X POST "https://api.wavespeed.ai/api/v3/black-forest-labs/flux-3/video-extend" \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $WAVESPEED_API_KEY" \
  -d "$REQUEST_BODY")

TASK=$(printf '%s' "$SUBMIT_RESPONSE" | jq 'if has("data") then .data else . end')
PREDICTION_ID=$(printf '%s' "$TASK" | jq -r '.id')
if [ -z "$PREDICTION_ID" ] || [ "$PREDICTION_ID" = "null" ]; then
  printf 'Submission response did not contain a prediction id
' >&2
  exit 1
fi
RESULT_URL=$(printf '%s' "$TASK" | jq -r '.urls.get // empty')
if [ -z "$RESULT_URL" ]; then
  RESULT_URL="https://api.wavespeed.ai/api/v3/predictions/$PREDICTION_ID/result"
fi

# 2. Poll until the prediction finishes.
while true; do
  RESPONSE=$(curl --silent --show-error --fail-with-body "$RESULT_URL" \
    -H "Authorization: Bearer $WAVESPEED_API_KEY")
  RESULT=$(printf '%s' "$RESPONSE" | jq 'if has("data") then .data else . end')
  STATUS=$(printf '%s' "$RESULT" | jq -r '.status')
  case "$STATUS" in
    completed) printf '%s\n' "$RESULT" | jq '.outputs'; break ;;
    failed|cancelled|timeout) printf '%s\n' "$RESULT" | jq . >&2; exit 1 ;;
    created|processing) sleep 2 ;;
    *) printf 'Unexpected status: %s
' "$STATUS" >&2; exit 1 ;;
  esac
done
Node.js example
const submitUrl = "https://api.wavespeed.ai/api/v3/black-forest-labs/flux-3/video-extend";
const apiKey = process.env.WAVESPEED_API_KEY;
if (!apiKey) throw new Error('Set WAVESPEED_API_KEY');

async function requestJson(url, options = {}) {
  const response = await fetch(url, options);
  if (!response.ok) throw new Error(await response.text());
  return response.json();
}

// 1. Submit the prediction.
const body = await requestJson(submitUrl, {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${apiKey}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
        "prompt": "A cinematic shot of a city at sunset, soft golden light",
        "video": "https://interactive-examples.mdn.mozilla.net/media/cc0-videos/flower.mp4",
        "aspect_ratio": "21:9",
        "resolution": "720p",
        "duration": 5,
        "generate_audio": true
}),
});
const task = body.data ?? body;
if (!task.id) throw new Error("Submission response did not contain a prediction id");
const resultUrl = task.urls?.get ||
  `https://api.wavespeed.ai/api/v3/predictions/${task.id}/result`;

// 2. Poll until the prediction finishes.
while (true) {
  const resultBody = await requestJson(resultUrl, {
    headers: { "Authorization": `Bearer ${apiKey}` },
  });
  const result = resultBody.data ?? resultBody;
  if (result.status === "completed") {
    console.log(result.outputs);
    break;
  }
  if (["failed", "cancelled", "timeout"].includes(result.status)) throw new Error(JSON.stringify(result));
  if (!["created", "processing"].includes(result.status)) throw new Error("Unexpected status: " + result.status);
  await new Promise(resolve => setTimeout(resolve, 2000));
}
Python example
import json
import os
import time
from urllib.request import Request, urlopen

api_key = os.environ["WAVESPEED_API_KEY"]
headers = {"Authorization": f"Bearer {api_key}", "Content-Type": "application/json"}
payload = {
    "prompt": "A cinematic shot of a city at sunset, soft golden light",
    "video": "https://interactive-examples.mdn.mozilla.net/media/cc0-videos/flower.mp4",
    "aspect_ratio": "21:9",
    "resolution": "720p",
    "duration": 5,
    "generate_audio": True
}

def request_json(url, data=None):
    request = Request(url, data=data, headers=headers, method="POST" if data else "GET")
    with urlopen(request) as response:
        return json.load(response)

# 1. Submit the prediction.
body = request_json("https://api.wavespeed.ai/api/v3/black-forest-labs/flux-3/video-extend", json.dumps(payload).encode())
task = body.get("data", body)
if not task.get("id"):
    raise RuntimeError("Submission response did not contain a prediction id")
result_url = task.get("urls", {}).get("get") or f"https://api.wavespeed.ai/api/v3/predictions/{task['id']}/result"

# 2. Poll until the prediction finishes.
while True:
    result_body = request_json(result_url)
    result = result_body.get("data", result_body)
    status = result.get("status")
    if status == "completed":
        print(result.get("outputs", []))
        break
    if status in {"failed", "cancelled", "timeout"}:
        raise RuntimeError(result)
    if status not in {"created", "processing"}:
        raise RuntimeError(f"Unexpected status: {status}")
    time.sleep(2)

Flux 3 Video Extend API — Frequently asked questions

What is the Flux 3 Video Extend API?

Flux 3 Video Extend is a Black Forest Labs model for video extension, exposed as a REST API on WaveSpeedAI. FLUX 3 Video Extend continues input videos into new 5-20 second clips, using prompt guidance to control the next action, camera movement, visual style, motion continuity, and optional synchronized audio at 720P / 1080P output. Ready-to-use REST inference API, best performance, no coldstarts, affordable pricing. You can call it programmatically or try it from the playground above.

How do I call the Flux 3 Video Extend API?

POST your input parameters to the model's REST endpoint (shown in the API tab of this playground) with your WaveSpeedAI API key in the Authorization header. Submission returns a prediction ID. Poll the result endpoint starting around every 2 seconds, increase the interval for long-running tasks, and stop on any terminal status. The playground generates production-oriented Python, JavaScript, and cURL examples with timeouts, transient-error handling, and safe GET retries. Full request/response shape is documented at https://wavespeed.ai/docs/docs-api/black-forest-labs/black-forest-labs-flux-3-video-extend.

How much does Flux 3 Video Extend cost per run?

Flux 3 Video Extend starts at $0.85 per run. That figure is the base price — the final charge scales with the parameters you set in the form (output size, length, count, references, or whatever knobs this model exposes), so a higher-quality or larger output costs more than a minimal one. The exact cost for your current input is shown live next to the Generate button before you submit, and the actual per-call charge is recorded on the prediction afterwards.

What inputs does Flux 3 Video Extend accept?

Key inputs: `prompt`, `video`, `aspect_ratio`, `resolution`, `duration`, `generate_audio`. The full JSON schema (types, defaults, allowed values) is rendered above the Generate button and mirrored in the API reference at https://wavespeed.ai/docs/docs-api/black-forest-labs/black-forest-labs-flux-3-video-extend.

How do I get started with the Flux 3 Video Extend API?

Sign up for a free WaveSpeedAI account to claim starter credits, copy your API key from /accesskey, then call the endpoint shown in the API tab of the playground. The playground also auto-generates a code sample in Python, JavaScript, or cURL for the parameters you've set.

Can I use Flux 3 Video Extend outputs commercially?

Commercial usage rights depend on the model's license, set by its provider (Black Forest Labs). The license summary appears on the model card above; see WaveSpeedAI's Terms of Service for platform-level conditions.

FLUX 3 Video Extend API on WaveSpeedAI