Extend Videos

January 29, 2026 (August 11, 2026)

Table of contents

  1. Request Headers
  2. Request Body
  3. Responses
  4. Model
  5. Missing media URLs
    1. How to get the link
  6. Examples
  7. Try It

Extend a previously generated video with a new prompt. Creates an additional 8-second segment that continues from the last ~1 second of the source video.

  • Video extension requires a paid Google AI subscription with remaining credits.
  • The extended video inherits the aspect ratio from the source video (landscape or portrait).
  • Extended videos have ~1 second overlap with the source video’s last frame. Use trimStart in POST /videos/concatenate to remove overlap when combining clips.

https://api.useapi.net/v1/google-flow/videos/extend

Request Headers 

Authorization: Bearer {API token}
Content-Type: application/json

Request Body 

{
  "mediaGenerationId": "user:12345-email:6a6f...-video:CAMaJDMx...",
  "prompt": "The camera slowly pans right revealing a majestic waterfall"
}
  • mediaGenerationId is required. The mediaGenerationId from a previously generated or extended video via POST /videos or POST /videos/extend. The source video must be Veo-generated — omni-flash videos cannot be extended here. To extend an Omni clip, chain V2V edits with referenceVideo_1 on POST /videos and join them with concatenate, see Video reference for how to keep the joins invisible.
  • prompt is required. Text description for the video extension (what happens next).
  • model is optional. Video generation model (default: veo-3.1-fast). Supported values: veo-3.1-fast, veo-3.1-quality, veo-3.1-lite, veo-3.1-lite-low-priority (Ultra $199 only, no credits, lower priority). On an account invited to an Ultra $199 family plan, veo-3.1-lite-low-priority isn’t available — only the plan owner’s account has it — and the request returns 400.
  • count is optional. Number of video variations to generate (1-4, default: 1). Each variation uses a different seed.
  • seed is optional. Random seed for reproducible results. If not specified, a random seed is generated. When count > 1, seeds are incremented (seed, seed+1, seed+2, …).
  • async is optional, enables fire-and-forget mode (default: false). When true, returns immediately with 201 Created and job metadata. Poll GET /jobs/jobId for completion status.
  • replyUrl is optional, webhook URL for job status callbacks. Receives POST requests with job status updates (created, started, completed, failed). The JSON payload shape matches GET /jobs/jobId response.
  • replyRef is optional, custom reference string passed back in webhook callbacks.
  • captchaToken, captchaRetry, captchaOrder are optional, mutually exclusive captcha parameters. See Captcha Parameters for details.

Responses

  • 200 OK

    Video extended successfully. All video data is in the media[] array.

    {
  "jobId": "j1737312345678v-u12345-email:jo***@gmail.com-bot:google-flow",
  "media": [
    {
      "name": "a1d95d21-75d2-482d-a354-14ef8802ce66",
      "projectId": "9f63078c-...redacted...",
      "workflowId": "fa986834-...redacted...",
      "workflowStepId": "CAE",
      "mediaMetadata": {
        "createTime": "2026-05-20T23:14:02.931677Z",
        "mediaTitle": "The camera slowly pans right revealing a majestic waterfall",
        "requestData": { "videoGenerationRequestData": { "...": "..." }, "clientPlatform": "CLIENT_PLATFORM_WEB" },
        "mediaStatus": { "mediaGenerationStatus": "MEDIA_GENERATION_STATUS_SUCCESSFUL" },
        "visibility": "PRIVATE",
        "mediaBlobSize": 4024251
      },
      "video": {
        "generatedVideo": {
          "seed": 987654321,
          "prompt": "The camera slowly pans right revealing a majestic waterfall",
          "model": "veo_3_1_t2v",
          "baseImageMediaGenerationId": "",
          "isLooped": false,
          "aspectRatio": "VIDEO_ASPECT_RATIO_LANDSCAPE"
        },
        "dimensions": { "length": "8s" },
        "operation": { "name": "a1d95d21-...redacted..." }
      },
      "mediaGenerationId": "user:12345-email:6a6f...-video:a1d95d21-...redacted...",
      "videoUrl": "https://flow-content.google/video/a1d95d21-...redacted...?Expires=...",
      "thumbnailUrl": "https://flow-content.google/image/a1d95d21-...redacted...?Expires=..."
    }
  ],
  "operations": [],
  "remainingCredits": 18760,
  "captcha": {
    "service": "AntiCaptcha",
    "taskId": "abc123...",
    "durationMs": 3500,
    "attempts": [
      {
        "service": "AntiCaptcha",
        "taskId": "abc123...",
        "durationMs": 3500,
        "success": true
      }
    ]
  }
}

  • 201 Created

    Job created in async mode (async: true). Video extension is processing in the background.

    Use GET /jobs/jobId to poll for completion status.

    {
  "jobid": "j1737312345678v-u12345-email:jo***@gmail.com-bot:google-flow",
  "type": "video",
  "status": "created",
  "created": "2026-01-29T12:34:56.789Z",
  "request": {
    "async": true,
    "prompt": "The camera slowly pans right revealing a majestic waterfall",
    "mediaGenerationId": "user:12345-email:6a6f...-video:CAMaJDMx..."
  },
  "response": {
    "captcha": {
      "service": "AntiCaptcha",
      "taskId": "14af1dbb-885c-4e25-8121-7a79489dfd0e",
      "durationMs": 5357
    }
  }
}

  • 400 Bad Request

    Invalid request.

    {
  "error": "Error message",
  "code": 400
}

  • 401 Unauthorized

    Invalid API token.

    {
  "error": "Unauthorized"
}

  • 403 Forbidden

    Google rejected the captcha on every try. We retry with a fresh captcha as many times as you allow (captchaRetry, default 5, or the providers in captchaOrder) and return this 403 only when all of them were rejected. The top-level error starts with captcha_quality:, for example "captcha_quality: PUBLIC_ERROR_UNUSUAL_ACTIVITY after 5 attempts — see GET /accounts/captcha-stats summary.by_account".

    One 403 is not a captcha problem. PUBLIC_ERROR_MODEL_ACCESS_DENIED in the response means Google refused the model on that account, so raising captchaRetry or adding providers will not help. Check that the account’s plan includes the model. Since 2026-09-23 Google no longer offers veo-3.1-lite-low-priority to invited members of an Ultra $199 family plan — only the family manager’s account keeps it.

    Nothing was created when this happens. Google checks the captcha before it starts generating, so no Google credits were used and you can resubmit straight away. Your captcha provider still bills each solve.

    The usual cause is the Google account, not the captcha provider. Google gives each account its own trust level. On a trusted account it accepts about 9 in 10 captchas, on a distrusted one about 3 in 10, whichever provider solved them. Most customers have a few distrusted accounts among many good ones.

    To see which accounts are affected, use GET /accounts/captcha-stats. Its summary.by_account shows, for each of your Google accounts, how many captchas were tried and what share Google accepted. GET account/stats with bot=google-flow also shows how many requests each account finished with each response code.

    • If one or a few accounts are far below the others, the API already sends them less work: when you leave out email, each captcha Google rejected on an account in the last 15 minutes lowers its chance of being picked, for generations and for image uploads. They still get some work, so an account that recovers gets its full share back. If you pin requests with email, move them to your other accounts yourself. Replace an account that stays low for more than a day or two.
    • If all your accounts drop at the same time, it’s the captcha provider. Configure at least two providers with POST /accounts/captcha-providers, and the API will start with whichever one Google accepts best.

    A higher captchaRetry gets more requests through on a distrusted account, but every extra try is another paid solve.

  • 404 Not Found

    Account not found or video not found.

    {
  "error": "Google Flow account [email protected] not found"
}

  • 408 Request Timeout

    Video extension polling timeout (after 10 minutes).

    {
  "error": "Polling timeout"
}

  • 429 Too Many Requests

    Google returns several RESOURCE_EXHAUSTED 429 variants. Check the reason field and respond accordingly:

    Reason Meaning Scope What to do Cooldown
    PUBLIC_ERROR_
    USER_REQUESTS_THROTTLED    		 Google is throttling the account (the token was fine). Uploads and generation are metered separately All models on the account — or uploads only, when POST /assets triggered it Run fewer parallel requests, or switch accounts. From POST /assets, retrying the same one rarely clears it ~30 min. From POST /assets, treat it as a minimum — it can persist
    PUBLIC_ERROR_
    USER_QUOTA_REACHED    		 Account’s overall Flow quota cap All models on the account Add accounts, or omit email to load-balance ~30 min
    PUBLIC_ERROR_
    PER_MODEL_DAILY_QUOTA_REACHED    		 Per-model daily quota Only that model, on that account Switch model, or wait Next UTC midnight
    PUBLIC_ERROR_
    UNUSUAL_ACTIVITY_TOO_MUCH_TRAFFIC    		 Google rejected the captcha on every try (we already retried). Usually a distrusted Google account, sometimes the provider Per request Check which accounts are affected in captcha-stats. Rest or replace those accounts. Add a second provider if all accounts drop together 60s

    Every 429 returns the cooldown two ways — an HTTP Retry-After: <seconds> header and a body retryAfter: <ISO timestamp> field. Honor it before retrying.

    When email is omitted, the first three reasons quarantine the account and the load balancer routes around it. If every account is quarantined for the model you get 429 with error: "no_eligible_account". Routing details: GET /jobs › Load Balancing Algorithm.

    Captcha-quality failures prefix the top-level error with captcha_quality: (e.g. "captcha_quality: PUBLIC_ERROR_UNUSUAL_ACTIVITY_TOO_MUCH_TRAFFIC after 3 attempts") so you can detect them without parsing the nested body.

  • 503 Service Unavailable

    503 has two distinct causes — check the response body to tell them apart.

    A transient Google-side outage. Wait 5-10 seconds and retry.

    {
  "error": {
    "code": 503,
    "message": "Service temporarily unavailable.",
    "status": "UNAVAILABLE"
  }
}

    A captcha-provider failure — the top-level error is prefixed Captcha service failed:. The problem is your captcha provider (check its API key and balance), not Google. Don’t retry until the provider is back.

    {
  "error": "Captcha service failed: ERROR_ZERO_BALANCE",
  "code": 503
}

Model

  • Video extension completed. Returns extended video data with signed URLs.

    {
  jobId: string                              // Job identifier
  media: Array<{                             // Preferred — use this instead of operations
    name: string                             // Media identifier (raw UUID)
    projectId: string
    workflowId?: string
    workflowStepId?: string                  // e.g. "CAE"
    mediaMetadata: {
      createTime?: string                    // ISO 8601 timestamp
      mediaTitle?: string                    // Extension prompt
      requestData?: object                   // Full Google Flow request payload
      mediaStatus: {
        mediaGenerationStatus: string        // MEDIA_GENERATION_STATUS_SUCCESSFUL | FAILED
        error?: { code: number; message: string }
      }
      visibility?: string
      mediaBlobSize?: number                 // Size of the MP4 in bytes
    }
    video?: {
      generatedVideo: {
        seed: number
        prompt?: string                      // Extension prompt
        model: string                        // veo_3_1_t2v
        baseImageMediaGenerationId?: string  // Source video media ID
        isLooped: boolean
        aspectRatio: string                  // VIDEO_ASPECT_RATIO_LANDSCAPE | PORTRAIT
      }
      dimensions?: { length?: string }       // Duration string (e.g. "8s")
      operation: { name: string }
    }
    mediaGenerationId: string                // Encoded reference ID for use in subsequent API calls
    videoUrl?: string                        // Signed video download URL (MP4, valid ~6h)
    thumbnailUrl?: string                    // Signed thumbnail download URL (JPEG, valid ~6h)
  }>
  operations: []                             // Always empty on this endpoint — read media[]
  remainingCredits?: number
  captcha?: {                                // Captcha metadata
    service: string                          // "CapSolver" | "AntiCaptcha" | "YesCaptcha" | "CapMonster" | "SolveCaptcha" | "2Captcha" | "EzCaptcha" | "UserProvided"
    taskId?: string
    durationMs: number
    attempts: Array<{
      service: string
      taskId?: string
      durationMs: number
      success: boolean
      error?: string
    }>
  }
}

  • Job created and processing in background. Structure matches GET /jobs/jobId response.

    {
  jobid: string                              // Job identifier
  type: 'video'                              // Job type
  status: 'created'                          // Job status
  created: string                            // ISO 8601 timestamp
  request: {
    async: true
    prompt: string                           // Extension prompt
    mediaGenerationId: string                // Source video reference
    model?: string                           // "veo-3.1-fast"
    seed?: number
    replyUrl?: string
    replyRef?: string
  }
  response: {
    captcha?: {                              // Present when captcha was used
      service: string                        // Provider or "UserProvided"
      taskId?: string                        // Absent for UserProvided
      durationMs: number
    }
  }
}

  • Error response structure.

    {
  jobId?: string                             // Present for job-related errors
  error: string                              // Error summary message
  code?: number                              // HTTP status code
  response?: {                               // API response with error details
    error?: {
      code: number
      message: string
      status: string
      details?: Array<{
        '@type': string
        reason: string
      }>
    }
  }
}

Missing media URLs

Media URL fields are optional and can be absent even when generation succeeded. When videoUrl, thumbnailUrl, fifeUrl, servingBaseUri, previewUrl or audioUrl is missing, the media itself is fine — only the download link could not be produced at that moment.

This is rare. Across the seven days of request logs we keep, it happened on one day only — twice, for about four hours and about forty minutes — and not at all on the other six. Google issues those links from an endpoint that limits how often it will answer a given network address, so it is Google limiting our outbound calls rather than useapi.net limiting you, and nothing you do triggers it. While it lasts it affects every account generating at that moment, then clears on its own. Your generation still completed and was charged as usual.

On a media item that generated successfully — mediaStatus.mediaGenerationStatus is MEDIA_GENERATION_STATUS_SUCCESSFUL — a missing URL means “not yet”, not “failed”, so read the field before using it and treat its absence as a retry condition. A media item that failed generation never carries a URL, and retrying will not produce one.

const url = media.videoUrl;
if (!url) {
  // Not an error — the link is not available yet. See the options below.
}

Which route to use depends on whether you can wait.

If you are already polling the job, do nothing special. Completed video jobs re-resolve missing URLs automatically on GET /jobs/jobId, and the recovered link is saved, so a later poll returns it with no extra work on your side. This applies to video jobs created within the last 24 hours. Once the job is completed and a URL is still missing, leave at least a minute between polls — a job re-resolves at most once a minute, and the block clears only once traffic stops, so a tight retry loop lengthens the wait rather than shortening it.

If you hold a mediaGenerationId but no longer have the job, ask for that one media again with GET /assets/mediaGenerationId. That endpoint says which case you are in rather than leaving you to guess. A 503 with a Retry-After header means the link is coming and tells you how long to wait, so wait that long and ask again. A 404 means Google has no such media, and no amount of retrying will change it.

If you cannot wait, download the video through us with GET /assets/mediaGenerationId?raw=true. It reads the media over a different Google route that the block does not touch, so it works immediately and keeps working while the other two return nothing. It is video only.

Prefer the two link-based routes when you can. They hand you a link and you download straight from Google. The raw form moves the whole file through useapi.net on every call, which makes it a way out of a stuck download rather than your normal download path.

Characters and voices resolve their URLs as they are read, so simply requesting GET /characters/ref or GET /voices/ref again is enough. Wait a minute before retrying — a response that came back without its URL is held briefly, so an immediate repeat returns the same one.

None of this applies to images. Whenever an image URL is missing, POST /images puts the image itself in the response instead, base64-encoded in encodedImage — so you already have the picture and there is nothing to retry.

Examples 

  • # First generate a video
curl -X POST \
     -H "Authorization: Bearer YOUR_API_TOKEN" \
     -H "Content-Type: application/json" \
     -d '{"prompt": "A serene mountain landscape at sunset"}' \
     "https://api.useapi.net/v1/google-flow/videos" > generate.json

# Extract mediaGenerationId from the response
MEDIA_ID=$(jq -r '.media[0].mediaGenerationId' generate.json)

# Extend the video
curl -X POST \
     -H "Authorization: Bearer YOUR_API_TOKEN" \
     -H "Content-Type: application/json" \
     -d "{\"mediaGenerationId\": \"$MEDIA_ID\", \"prompt\": \"The camera slowly pans right revealing a majestic waterfall\"}" \
     "https://api.useapi.net/v1/google-flow/videos/extend" > extend.json

# Extract extended video URL and download
VIDEO_URL=$(jq -r '.media[0].videoUrl' extend.json)
curl "$VIDEO_URL" --output extended_video.mp4

  • const token = 'YOUR_API_TOKEN';

// First generate a video
const generateResponse = await fetch('https://api.useapi.net/v1/google-flow/videos', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${token}`,
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    prompt: 'A serene mountain landscape at sunset'
  })
});

const generated = await generateResponse.json();
// Prefer media[] over deprecated operations[]
const mediaGenerationId = generated.media[0].mediaGenerationId;

// Extend the video
const extendResponse = await fetch('https://api.useapi.net/v1/google-flow/videos/extend', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${token}`,
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    mediaGenerationId,
    prompt: 'The camera slowly pans right revealing a majestic waterfall'
  })
});

const extended = await extendResponse.json();
// Prefer media[] over deprecated operations[]
const videoUrl = extended.media[0].videoUrl;

// Download extended video (Node.js)
const videoResponse = await fetch(videoUrl);
const videoBuffer = await videoResponse.arrayBuffer();
require('fs').writeFileSync('extended_video.mp4', Buffer.from(videoBuffer));
console.log('Extended video saved!');

  • import requests

token = 'YOUR_API_TOKEN'
headers = {
    'Authorization': f'Bearer {token}',
    'Content-Type': 'application/json'
}

# First generate a video
generate_response = requests.post(
    'https://api.useapi.net/v1/google-flow/videos',
    headers=headers,
    json={'prompt': 'A serene mountain landscape at sunset'}
)
generated = generate_response.json()
# Prefer media[] over deprecated operations[]
media_generation_id = generated['media'][0]['mediaGenerationId']

# Extend the video
extend_response = requests.post(
    'https://api.useapi.net/v1/google-flow/videos/extend',
    headers=headers,
    json={
        'mediaGenerationId': media_generation_id,
        'prompt': 'The camera slowly pans right revealing a majestic waterfall'
    }
)
extended = extend_response.json()
# Prefer media[] over deprecated operations[]
video_url = extended['media'][0]['videoUrl']

# Download extended video
video_response = requests.get(video_url)
with open('extended_video.mp4', 'wb') as f:
    f.write(video_response.content)
print('Extended video saved!')

Try It