Black Forest Labs Flux 3 Video Extend Draft API Documentation

Black Forest Labs Flux 3 Video Extend Draft API Documentation

Playground

FLUX 3 Video Extend Draft quickly continues a required input video into a draft clip with prompt-guided next-scene motion, optional synchronized audio, and flexible 5-20 second duration for rapid iteration.

Features

FLUX 3 Draft Video Extend quickly continues a required input video into a draft extension guided by your prompt. Use it to test what should happen next, how the camera should move, and how the visual style should continue before moving to a final-quality workflow.

Why Choose This?

• Video extension draft generation
  Continue an existing video with a prompt-guided draft extension.

• Fast continuation testing
  Test next-scene action, visual continuity, subject behavior, camera movement, pacing, and atmosphere.

• Prompt-guided scene development
  Describe how the video should continue after the source clip ends.

• Optional synchronized audio
  Generate matching audio for early ambience, effects, music, or dialogue tests.

• Flexible duration
  Choose a draft extension duration from 5 to 20 seconds.

• Multiple aspect ratios
  Supports landscape, portrait, square, and cinematic formats.

Parameters

How to Use

1. Upload the source video — Provide an MP4 video under 50 MB and under 15 seconds.
2. Write the prompt — Describe the next event, action, camera movement, lighting, mood, and continuity direction.
3. Choose aspect ratio — Select the output format that matches your target use case.
4. Set duration — Choose a draft extension duration from 5 to 20 seconds.
5. Configure audio optional — Enable generate_audio when you want to test ambience, effects, music, or dialogue.
6. Submit — Generate the draft continuation and review the extended result.

Pricing

Pricing is based on billed extension duration.

Billed duration is rounded up to the next whole second and capped at 20 seconds. Audio generation does not add a separate charge.

Example Costs

Best Use Cases

• Next-scene testing — Explore different continuations after an existing clip ends.
• Alternative endings — Generate multiple draft endings from the same source video.
• Product demo extension — Continue product motion, camera movement, or feature reveals.
• Character action continuation — Extend character movement, gestures, reactions, or performance.
• Advertising drafts — Test campaign ideas, transitions, and pacing from existing footage.
• Social video concepts — Extend short clips into draft vertical, square, or widescreen content.

Pro Tips

• Begin with the next visible action instead of repeating the entire source video.
• State continuity requirements such as lighting, subject appearance, environment, camera movement, and mood.
• Describe what should happen immediately after the source video ends.
• Keep the draft prompt focused on one clear continuation event.
• Use shorter durations for quick tests and longer durations when the continuation needs more time to develop.
• Use a clean source video with a clear ending moment for smoother continuation.

Related Models

• FLUX 3 Draft Start-End-to-Video — Generate a draft transition between a start image and an end image.
• FLUX 3 Draft Image-to-Video — Animate a reference image into a draft video.
• FLUX 3 Draft Text-to-Video — Generate draft videos directly from text prompts.

Authentication

For authentication details, please refer to the Authentication Guide.

API Endpoints

Submit Task & Query Result

set -euo pipefail

export WAVESPEED_API_KEY="your-api-key"

REQUEST_BODY=$(cat <<'JSON'
{
  "prompt": "A cinematic ocean wave at sunrise, highly detailed",
  "video": "https://interactive-examples.mdn.mozilla.net/media/cc0-videos/flower.mp4",
  "aspect_ratio": "21:9",
  "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-draft" \
  -H "Authorization: Bearer ${WAVESPEED_API_KEY}" \
  -H "Content-Type: application/json" \
  -d "${REQUEST_BODY}")

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

# 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' "${RESPONSE}" | jq 'if type == "object" and has("data") then .data else . end')
  STATUS=$(printf '%s' "${RESULT}" | jq -r '.status // empty')

  case "${STATUS}" in
    completed) printf '%s\n' "${RESULT}" | jq '.outputs'; break ;;
    failed|cancelled|timeout|deleted) printf '%s\n' "${RESULT}" | jq . >&2; exit 1 ;;
    *) sleep 2 ;;
  esac
done

Parameters

Task Submission Parameters

Request Parameters

Response Parameters

Result Request Parameters

Result Response Parameters