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kwaivgi/kling-v4.0/video-extend

Kling V4.0 Video Extend continues a video from its last frame with a new 3 to 30 second segment guided by your prompt, at 720p or 1080p with synchronized stereo audio, and returns the original and the new segment joined. Ready-to-use REST inference API, best performance, no coldstarts, affordable pricing.

Video Extension
Input

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Idle

$0.785per run·~12 / $10

ExamplesView all

The sailboat keeps gliding forward as the camera slowly rises above the water, revealing a quiet harbor; gulls cross the golden sky, soft wind and gentle waves.

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README

Kling V4.0 Video Extend

Kling V4.0 Video Extend continues a video from its last frame. It generates a new segment of 3 to 30 seconds that follows your prompt, with synchronized stereo audio, and returns the original video and the new segment joined into one clip. Output is 720p or 1080p.

Why Choose This?

  • Continue any video Pick up exactly where your clip ends, with the same subject, setting and style.
  • Up to 30 seconds more Any length from 3 to 30 seconds for the new segment.
  • Native audio The new segment comes with stereo sound generated together with the picture; your original audio is kept.
  • Aim for an ending frame Add a last image and the new segment moves from the end of your video toward it.

Pricing

Only the new segment is charged, per second of the generated video:

ResolutionPrice per second
720p$0.157
1080p$0.235

For example, adding a 5 second segment at 720p costs $0.785.

Parameters

ParameterDescription
videoRequired. The video to extend. The new segment is generated from its last frame and appended to the original.
promptRequired. Describe the continuation: action, camera movement, lighting and sound.
durationLength of the new segment in seconds, 3 to 30 (default 5).
resolution720p (default) or 1080p.
last_imageOptional target last-frame image. The new segment moves from the video's last frame toward it.

Prompting Guide

  • Describe what happens next, not what is already on screen: "the camera slowly pushes in as he looks up".
  • Keep the continuation consistent with the end of your clip so the join feels natural.
  • Match the length to the action: a short segment for one move, a longer one for a developing scene.
  • Describe sound you want to hear (ambience, music, a line of dialogue) in the prompt.
Note:This website uses AI models provided by third parties. Documentation prices are for reference and may be outdated. The Generate button shows an estimate; the final task charge prevails.

Kling v4.0 Video Extend API — Quick start

Grab a WaveSpeedAI API key, then call POST https://api.wavespeed.ai/api/v3/kwaivgi/kling-v4.0/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 Kling v4.0 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",
    "resolution": "720p",
    "duration": 5
}
JSON
)

# 1. Submit the prediction.
SUBMIT_RESPONSE=$(curl --silent --show-error --fail-with-body \
  -X POST "https://api.wavespeed.ai/api/v3/kwaivgi/kling-v4.0/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="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' "$RESPONSE" | jq 'if has("data") then .data else . end')
  STATUS=$(printf '%s' "$RESULT" | jq -r '.status')
  case "$STATUS" in
    completed) printf '%s\n' "$RESULT" | jq '.outputs'; break ;;
    failed|cancelled|timeout|deleted) printf '%s\n' "$RESULT" | jq . >&2; exit 1 ;;
    *) sleep 2 ;;
  esac
done
Node.js example
const submitUrl = "https://api.wavespeed.ai/api/v3/kwaivgi/kling-v4.0/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 ${apiKey}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
        "prompt": "A cinematic shot of a city at sunset, soft golden light",
        "video": "https://interactive-examples.mdn.mozilla.net/media/cc0-videos/flower.mp4",
        "resolution": "720p",
        "duration": 5
}),
});
const task = body.data ?? body;
if (!task.id) throw new Error("Submission response did not contain a prediction id");
const resultUrl = `https://api.wavespeed.ai/api/v3/predictions/${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", "deleted"].includes(result.status)) throw new Error(JSON.stringify(result));
  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",
    "resolution": "720p",
    "duration": 5
}

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/kwaivgi/kling-v4.0/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 = 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", "deleted"}:
        raise RuntimeError(result)
    time.sleep(2)

Kling v4.0 Video Extend API — Frequently asked questions

What is the Kling v4.0 Video Extend API?

Kling v4.0 Video Extend is a Kuaishou model for video extension, exposed as a REST API on WaveSpeedAI. Kling V4.0 Video Extend continues a video from its last frame with a new 3 to 30 second segment guided by your prompt, at 720p or 1080p with synchronized stereo audio, and returns the original and the new segment joined. 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 Kling v4.0 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 Python, JavaScript, and cURL examples for submitting requests and polling results. Full request/response shape is documented at https://wavespeed.ai/docs/docs-api/kwaivgi/kwaivgi-kling-v4.0-video-extend.

How much does Kling v4.0 Video Extend cost per run?

Kling v4.0 Video Extend starts at $0.785 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 Kling v4.0 Video Extend accept?

Key inputs: `prompt`, `video`, `resolution`, `duration`, `last_image`. 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/kwaivgi/kwaivgi-kling-v4.0-video-extend.

How do I get started with the Kling v4.0 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 Kling v4.0 Video Extend outputs commercially?

Commercial usage rights depend on the model's license, set by its provider (Kuaishou). Check the provider's applicable terms and WaveSpeedAI's Terms of Service before commercial use.

llms.txt — kwaivgi/kling-v4.0/video-extend for AI agents and LLMs