AI Video Extension Callbacks

When you submit a video extension task to the Runway API, you can set a callback address through the callBackUrl parameter. After the task is completed, the system will automatically push the results to your specified address.

Callback Mechanism Overview

TIP

The callback mechanism eliminates the need to poll the API for task status. The system proactively pushes task completion results to your server.

Callback Timing

The system sends callback notifications in the following situations:

• Video extension task successfully completed
• Video extension task failed
• Errors occurred during task processing

Callback Method

• HTTP Method: POST
• Content Type: application/json
• Timeout: 15 seconds

Callback Request Format

After task completion, the system will send a POST request to your callBackUrl in the following format:

Success Callback

{
  "code": 200,
  "msg": "All generated successfully.",
  "data": {
    "image_url": "https://file.com/m/xxxxxxxx.png",
    "task_id": "ee603959-debb-48d1-98c4-a6d1c717eba6",
    "video_id": "485da89c-7fca-4340-8c04-101025b2ae71",
    "video_url": "https://file.com/k/xxxxxxx.mp4"
  }
}

Failure Callback

{
  "code": 400,
  "msg": "Get image info failed.",
  "data": {
    "task_id": "ee603959-debb-48d1-98c4-a6d1c717eba6"
  }
}

Status Code Description

Parameter Description

Parameter	Type	Required	Description
code	integer	Yes	Callback status code indicating task processing result
msg	string	Yes	Status message providing detailed status description
data.task_id	string	Yes	Task ID, consistent with the taskId returned when you submitted the task
data.video_id	string	No	Video unique identifier (returned only on success)
data.video_url	string	No	Accessible video URL, valid for 14 days (returned only on success)
data.image_url	string	No	Cover image URL of the generated video (returned only on success)

Status Code Details

Status Code	Description
200	Success - Request has been processed successfully
400	Client Error - Request parameters are incorrect or content is inappropriate
500	Server Error - An unexpected error occurred while processing the request

Common Error Messages

When code is 400, possible error messages include:

• Get image info failed
• Inappropriate content detected. Please replace the image or video
• Incorrect image format
• Please try again later. You can upgrade to Standard membership to start generating now
• Reached the limit for concurrent generations
• Unsupported width or height. Please adjust the size and try again
• Upload failed due to network reasons, please re-enter
• Your prompt was caught by our AI moderator. Please adjust it and try again!
• Your prompt/negative prompt cannot exceed 2048 characters. Please check if your input is too long
• Your video creation prompt contains NSFW content, which isn't allowed under our policy. Kindly revise your prompt and generate again

Callback Reception Examples

Here are example codes for receiving callbacks in popular programming languages:

Node.js

const express = require('express');
const fs = require('fs');
const https = require('https');
const app = express();

app.use(express.json());

app.post('/runway-extend-callback', (req, res) => {
  const { code, msg, data } = req.body;
  
  console.log('Received Runway video extension callback:', {
    taskId: data.task_id,
    status: code,
    message: msg
  });
  
  if (code === 200) {
    // Video extension successful
    const { task_id, video_id, video_url, image_url } = data;
    
    console.log('Video extension successful!');
    console.log(`Task ID: ${task_id}`);
    console.log(`Video ID: ${video_id}`);
    console.log(`Video URL: ${video_url}`);
    console.log(`Cover URL: ${image_url}`);
    
    // Download video file
    if (video_url) {
      downloadFile(video_url, `runway_extend_${task_id}.mp4`)
        .then(() => console.log('Video download successful'))
        .catch(err => console.error('Video download failed:', err));
    }
    
    // Download cover image
    if (image_url) {
      downloadFile(image_url, `runway_extend_cover_${task_id}.png`)
        .then(() => console.log('Cover download successful'))
        .catch(err => console.error('Cover download failed:', err));
    }
    
  } else {
    // Video extension failed
    console.log('Runway video extension failed:', msg);
    
    // Handle specific error types
    if (code === 400) {
      console.log('Client error - Check input parameters and content');
    } else if (code === 500) {
      console.log('Server error - Please try again later');
    }
  }
  
  // Return 200 status code to confirm callback received
  res.status(200).json({ code: 200, msg: 'success' });
});

// Helper function: Download file
function downloadFile(url, filename) {
  return new Promise((resolve, reject) => {
    const file = fs.createWriteStream(filename);
    
    https.get(url, (response) => {
      if (response.statusCode === 200) {
        response.pipe(file);
        file.on('finish', () => {
          file.close();
          resolve();
        });
      } else {
        reject(new Error(`HTTP ${response.statusCode}`));
      }
    }).on('error', reject);
  });
}

app.listen(3000, () => {
  console.log('Callback server running on port 3000');
});

Python

from flask import Flask, request, jsonify
import requests
import os

app = Flask(__name__)

@app.route('/runway-extend-callback', methods=['POST'])
def handle_callback():
    data = request.json
    
    code = data.get('code')
    msg = data.get('msg')
    callback_data = data.get('data', {})
    task_id = callback_data.get('task_id')
    
    print(f"Received Runway video extension callback:")
    print(f"Task ID: {task_id}")
    print(f"Status: {code}, Message: {msg}")
    
    if code == 200:
        # Video extension successful
        video_id = callback_data.get('video_id')
        video_url = callback_data.get('video_url')
        image_url = callback_data.get('image_url')
        
        print("Video extension successful!")
        print(f"Video ID: {video_id}")
        print(f"Video URL: {video_url}")
        print(f"Cover URL: {image_url}")
        
        # Download video file
        if video_url:
            try:
                video_filename = f"runway_extend_{task_id}.mp4"
                download_file(video_url, video_filename)
                print("Video download successful")
            except Exception as e:
                print(f"Video download failed: {e}")
        
        # Download cover image
        if image_url:
            try:
                image_filename = f"runway_extend_cover_{task_id}.png"
                download_file(image_url, image_filename)
                print("Cover download successful")
            except Exception as e:
                print(f"Cover download failed: {e}")
                
    else:
        # Video extension failed
        print(f"Runway video extension failed: {msg}")
        
        # Handle specific error types
        if code == 400:
            print("Client error - Check input parameters and content")
            if 'Inappropriate content' in msg:
                print("Content moderation failed - Please replace image or video")
            elif 'Incorrect image format' in msg:
                print("Format error - Please check image format")
            elif 'concurrent generations' in msg:
                print("Concurrency limit - Please wait or upgrade membership")
            elif 'NSFW content' in msg:
                print("Content violation - Please modify prompt")
        elif code == 500:
            print("Server error - Please try again later")
    
    # Return 200 status code to confirm callback received
    return jsonify({'code': 200, 'msg': 'success'}), 200

def download_file(url, filename):
    """Download file from URL and save locally"""
    response = requests.get(url, stream=True)
    response.raise_for_status()
    
    os.makedirs('downloads', exist_ok=True)
    filepath = os.path.join('downloads', filename)
    
    with open(filepath, 'wb') as f:
        for chunk in response.iter_content(chunk_size=8192):
            f.write(chunk)

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=3000)

PHP

<?php
header('Content-Type: application/json');

// Get POST data
$input = file_get_contents('php://input');
$data = json_decode($input, true);

$code = $data['code'] ?? null;
$msg = $data['msg'] ?? '';
$callbackData = $data['data'] ?? [];
$taskId = $callbackData['task_id'] ?? '';

error_log("Received Runway video extension callback:");
error_log("Task ID: $taskId");
error_log("Status: $code, Message: $msg");

if ($code === 200) {
    // Video extension successful
    $videoId = $callbackData['video_id'] ?? '';
    $videoUrl = $callbackData['video_url'] ?? '';
    $imageUrl = $callbackData['image_url'] ?? '';
    
    error_log("Video extension successful!");
    error_log("Video ID: $videoId");
    error_log("Video URL: $videoUrl");
    error_log("Cover URL: $imageUrl");
    
    // Download video file
    if (!empty($videoUrl)) {
        try {
            $videoFilename = "runway_extend_{$taskId}.mp4";
            downloadFile($videoUrl, $videoFilename);
            error_log("Video download successful");
        } catch (Exception $e) {
            error_log("Video download failed: " . $e->getMessage());
        }
    }
    
    // Download cover image
    if (!empty($imageUrl)) {
        try {
            $imageFilename = "runway_extend_cover_{$taskId}.png";
            downloadFile($imageUrl, $imageFilename);
            error_log("Cover download successful");
        } catch (Exception $e) {
            error_log("Cover download failed: " . $e->getMessage());
        }
    }
    
} else {
    // Video extension failed
    error_log("Runway video extension failed: $msg");
    
    // Handle specific error types
    if ($code === 400) {
        error_log("Client error - Check input parameters and content");
        if (strpos($msg, 'Inappropriate content') !== false) {
            error_log("Content moderation failed - Please replace image or video");
        } elseif (strpos($msg, 'Incorrect image format') !== false) {
            error_log("Format error - Please check image format");
        } elseif (strpos($msg, 'concurrent generations') !== false) {
            error_log("Concurrency limit - Please wait or upgrade membership");
        } elseif (strpos($msg, 'NSFW content') !== false) {
            error_log("Content violation - Please modify prompt");
        }
    } elseif ($code === 500) {
        error_log("Server error - Please try again later");
    }
}

// Return 200 status code to confirm callback received
http_response_code(200);
echo json_encode(['code' => 200, 'msg' => 'success']);

function downloadFile($url, $filename) {
    $downloadDir = 'downloads';
    if (!is_dir($downloadDir)) {
        mkdir($downloadDir, 0755, true);
    }
    
    $filepath = $downloadDir . '/' . $filename;
    
    $fileContent = file_get_contents($url);
    if ($fileContent === false) {
        throw new Exception("Failed to download file from URL");
    }
    
    $result = file_put_contents($filepath, $fileContent);
    if ($result === false) {
        throw new Exception("Failed to save file locally");
    }
}
?>

Best Practices

Callback URL Configuration Recommendations

1. Use HTTPS: Ensure callback URL uses HTTPS protocol for secure data transmission
2. Verify Source: Verify the legitimacy of the request source in callback processing
3. Idempotent Processing: The same task_id may receive multiple callbacks, ensure processing logic is idempotent
4. Quick Response: Callback processing should return 200 status code promptly to avoid timeout
5. Asynchronous Processing: Complex business logic should be processed asynchronously to avoid blocking callback response
6. Timely Download: Video URLs are valid for only 14 days, please download and save promptly
7. Extension Management: Properly manage extended video files and cover images

:::caution Important Reminders

• Callback URL must be publicly accessible
• Server must respond within 15 seconds, otherwise it will be considered timeout
• After 3 consecutive retry failures, the system will stop sending callbacks
• Video URLs are valid for only 14 days, please download and save to your storage system promptly
• Ensure the stability of callback processing logic to avoid callback failures due to exceptions
• Properly handle content moderation errors to ensure input content complies with platform policies
• Extended videos are usually longer than original videos
• Pay attention to concurrent generation limits to avoid submitting too many tasks simultaneously

:::

Troubleshooting

If you don't receive callback notifications, please check the following:

• Confirm that the callback URL is accessible from the public internet

• Check firewall settings to ensure inbound requests are not blocked

• Verify domain name resolution is correct

• Ensure server returns HTTP 200 status code within 15 seconds

• Check server logs for error messages

• Verify interface path and HTTP method are correct

• Confirm that the received POST request body is in JSON format

• Check if Content-Type is application/json

• Verify JSON parsing is correct

• Confirm that video URL is accessible

• Check video download permissions and network connection

• Verify video save path and permissions

• Note the 14-day validity period limitation of video URLs

• Backup videos to long-term storage system promptly

• Review content moderation error messages

• Ensure input images or videos do not contain inappropriate content

• Check if prompts comply with platform policies

• Avoid using NSFW-related descriptive words

• Ensure image format is correct and dimensions are appropriate

• Monitor current concurrent task count

• Implement appropriate task queue mechanism

• Consider upgrading to Standard membership for higher concurrency limits

• Reasonably schedule task submission times

• Check coherence of extended videos

• Verify if video duration meets expectations

• Evaluate quality and style consistency of extended portions

• Ensure extended videos transition naturally

Extension-Specific Considerations

:::note AI Video Extension Features

AI video extension functionality continues generation based on existing videos with the following characteristics:

1. Duration Increase: Extended videos will be longer than original videos
2. Style Continuation: The system tries to maintain the visual style and motion patterns of the original video
3. Smooth Transition: Extended portions will naturally connect with the original video
4. Quality Preservation: Extended video quality should be comparable to the original video
5. Motion Coherence: Object movement and scene changes will maintain logical coherence
6. URL Validity: Generated video URLs are valid for only 14 days

:::

Alternative Approach

If you cannot use the callback mechanism, you can also use polling:

Poll Query Results

Use the Get AI Video Details interface to periodically query task status, recommended every 30 seconds.