Black Forest Labs Flux 3 Video Extend

Black Forest Labs Flux 3 Video Extend

Playground

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.

Features

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

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.

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

• FLUX 3 Start-End-to-Video — Generate video using both a starting frame and an ending frame.
• FLUX 3 Image-to-Video — Animate a reference image into a video.
• FLUX 3 Video Extend — Extend an existing video with new generated footage.
• FLUX 3 Text-to-Video — Generate video directly from a text prompt.

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",
  "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 "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 "${PREDICTION_ID}" ]; then
  printf 'Submission response did not contain a prediction id
' >&2
  exit 1
fi
RESULT_URL=$(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' "${RESPONSE}" | jq 'if type == "object" and has("data") then .data else . end')
  STATUS=$(printf '%s' "${RESULT}" | jq -r '.status // empty')

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

Parameters

Task Submission Parameters

Request Parameters

Response Parameters

Result Request Parameters

Result Response Parameters