> ## Documentation Index
> Fetch the complete documentation index at: https://docs.gptproto.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Veo-3.1-Fast-Generate-Preview - Video To Video

> Quick veo 3.1 video to video preview. Instantly restyle and transform existing videos with advanced AI generative effects.

## Authentication

1. Sign up for a GPTProto account at [https://gptproto.com](https://gptproto.com)
2. Navigate to the API Keys section in your dashboard
3. Generate a new API key (sk-xxxxx)
4. Copy and securely store your API key
   For authentication details, please refer to the [Authentication](https://docs.gptproto.com/authentication) section.

## Initiate Request

<CodeGroup>
  ```bash cURL theme={null}
  curl --location 'https://gptproto.com/v1beta/models/veo-3.1-fast-generate-preview:predictLongRunning' \
  --header 'x-goog-api-key: GPTPROTO_API_KEY' \
  --header 'Content-Type: application/json' \
  --data '{
    "instances": [
      {
        "prompt": "Replace the fox with a tiger",
        "video": {
          "uri": "https://oss.gptproto.com/ai/api1bfc42f3-af1f-4eb9-b91f-ae8fba044ac8.mp4"
        }
      }
    ],
    "parameters": {
      "resolution": "720p",
      "aspectRatio": "9:16"
    }
  }'

  ```

  ```javascript JavaScript theme={null}
  const axios = require('axios');
  let data = JSON.stringify({
    "instances": [
      {
        "prompt": "Replace the fox with a tiger",
        "video": {
          "uri": "https://oss.gptproto.com/ai/api1bfc42f3-af1f-4eb9-b91f-ae8fba044ac8.mp4"
        }
      }
    ],
    "parameters": {
      "resolution": "720p",
      "aspectRatio": "9:16"
    }
  });

  let config = {
    method: 'post',
    maxBodyLength: Infinity,
    url: 'https://gptproto.com/v1beta/models/veo-3.1-fast-generate-preview:predictLongRunning',
    headers: { 
      'x-goog-api-key': 'GPTPROTO_API_KEY', 
      'Content-Type': 'application/json'
    },
    data : data
  };

  axios.request(config)
  .then((response) => {
    console.log(JSON.stringify(response.data));
  })
  .catch((error) => {
    console.log(error);
  });


  ```

  ```python Python theme={null}
  import requests
  import json

  url = "https://gptproto.com/v1beta/models/veo-3.1-fast-generate-preview:predictLongRunning"

  payload = json.dumps({
    "instances": [
      {
        "prompt": "Replace the fox with a tiger",
        "video": {
          "uri": "https://oss.gptproto.com/ai/api1bfc42f3-af1f-4eb9-b91f-ae8fba044ac8.mp4"
        }
      }
    ],
    "parameters": {
      "resolution": "720p",
      "aspectRatio": "9:16"
    }
  })
  headers = {
    'x-goog-api-key': 'GPTPROTO_API_KEY',
    'Content-Type': 'application/json'
  }

  response = requests.request("POST", url, headers=headers, data=payload)

  print(response.text)


  ```

  ```go Go theme={null}
  package main

  import (
    "fmt"
    "strings"
    "net/http"
    "io"
  )

  func main() {

    url := "https://gptproto.com/v1beta/models/veo-3.1-fast-generate-preview:predictLongRunning"
    method := "POST"

    payload := strings.NewReader(`{
    "instances": [
      {
        "prompt": "Replace the fox with a tiger",
        "video": {
          "uri": "https://oss.gptproto.com/ai/api1bfc42f3-af1f-4eb9-b91f-ae8fba044ac8.mp4"
        }
      }
    ],
    "parameters": {
      "resolution": "720p",
      "aspectRatio": "9:16"
    }
  }`)

    client := &http.Client {
    }
    req, err := http.NewRequest(method, url, payload)

    if err != nil {
      fmt.Println(err)
      return
    }
    req.Header.Add("x-goog-api-key", "GPTPROTO_API_KEY")
    req.Header.Add("Content-Type", "application/json")

    res, err := client.Do(req)
    if err != nil {
      fmt.Println(err)
      return
    }
    defer res.Body.Close()

    body, err := io.ReadAll(res.Body)
    if err != nil {
      fmt.Println(err)
      return
    }
    fmt.Println(string(body))
  }

  ```
</CodeGroup>

## Query Result

After submitting a video generation request, the API returns an operation object. Use the operation name to poll for the result.

<CodeGroup>
  ```bash cURL theme={null}
  curl -X GET "https://api.gptproto.com/v1beta/models/{model}/operations/{operation_id}" \
    -H "x-goog-api-key: GPTPROTO_API_KEY" \
    -H "Content-Type: application/json"
  ```

  ```python Python theme={null}
  import requests

  url = "https://api.gptproto.com/v1beta/models/{model}/operations/{operation_id}"
  headers = {
      "x-goog-api-key": "GPTPROTO_API_KEY",
      "Content-Type": "application/json"
  }

  response = requests.get(url, headers=headers)
  result = response.json()
  print(result)
  ```

  ```javascript JavaScript theme={null}
  const url = "https://api.gptproto.com/v1beta/models/{model}/operations/{operation_id}";
  const headers = {
    "x-goog-api-key": "GPTPROTO_API_KEY",
    "Content-Type": "application/json"
  };

  fetch(url, { method: "GET", headers })
    .then(response => response.json())
    .then(data => console.log(data))
    .catch(error => console.error("Error:", error));
  ```
</CodeGroup>

<Note>
  Query URL uses `api.gptproto.com` domain. Replace `{model}` with the model name and `{operation_id}` with the operation ID from the generation response.
</Note>

<Accordion title="Response Example">
  ```json theme={null}
  {
    "name": "models/veo-3.1-generate-preview/operations/abc123",
    "done": true,
    "response": {
      "generateVideoResponse": {
        "generatedSamples": [
          {
            "video": {
              "uri": "https://api.gptproto.com/upload/v1beta/files/abc:download?alt=media",
              "encoding": "video/mp4"
            }
          }
        ]
      }
    }
  }
  ```
</Accordion>

## Download Video

Once the operation is complete, use the video URI from the response to download the generated video.

<CodeGroup>
  ```bash cURL theme={null}
  curl -L "https://api.gptproto.com/upload/v1beta/files/{file_id}:download?alt=media" \
    -H "x-goog-api-key: GPTPROTO_API_KEY" \
    -o output.mp4
  ```

  ```python Python theme={null}
  import requests

  url = "https://api.gptproto.com/upload/v1beta/files/{file_id}:download?alt=media"
  headers = {
      "x-goog-api-key": "GPTPROTO_API_KEY"
  }

  response = requests.get(url, headers=headers)
  with open("output.mp4", "wb") as f:
      f.write(response.content)
  print("Video saved to output.mp4")
  ```

  ```javascript JavaScript theme={null}
  const url = "https://api.gptproto.com/upload/v1beta/files/{file_id}:download?alt=media";
  const headers = {
    "x-goog-api-key": "GPTPROTO_API_KEY"
  };

  fetch(url, { headers })
    .then(response => response.blob())
    .then(blob => {
      const a = document.createElement("a");
      a.href = URL.createObjectURL(blob);
      a.download = "output.mp4";
      a.click();
    });
  ```
</CodeGroup>

<Note>
  Replace `{file_id}` with the file ID from the video URI in the query response (e.g. `abc` from `.../files/abc:download?alt=media`).
</Note>

## Parameters

### Path Parameters

Endpoint: `https://gptproto.com/v1beta/models/{model}:predictLongRunning`

| Model                           | Description                        |
| ------------------------------- | ---------------------------------- |
| `veo-3.1-generate-preview`      | Veo 3.1 standard — highest quality |
| `veo-3.1-fast-generate-preview` | Veo 3.1 Fast — optimized for speed |

### Request Body

The request uses Google's Vertex AI format with `instances` and `parameters` arrays.

#### instances\[0] — Core Parameters

| Parameter                  | Type   | Required | Default | Description                                                     |
| -------------------------- | ------ | -------- | ------- | --------------------------------------------------------------- |
| `prompt`                   | string | ✅ Yes    | -       | A text description of the desired video. Supports audio cues.   |
| `image`                    | object | ❌ No     | -       | Source image for image-to-video generation.                     |
| `image.mimeType`           | string | ❌ No     | -       | MIME type of the image (e.g. `image/png`, `image/jpeg`).        |
| `image.bytesBase64Encoded` | string | ❌ No     | -       | Base64-encoded image data.                                      |
| `video`                    | object | ❌ No     | -       | Source video for video-to-video generation (editing/extension). |
| `video.uri`                | string | ❌ No     | -       | URL of the source video.                                        |

#### parameters — Advanced Parameters

| Parameter          | Type    | Required | Default | Range                          | Description                                                                       |
| ------------------ | ------- | -------- | ------- | ------------------------------ | --------------------------------------------------------------------------------- |
| `aspectRatio`      | string  | ❌ No     | `16:9`  | `16:9`<br />`9:16`             | The aspect ratio of the generated video.                                          |
| `resolution`       | string  | ❌ No     | `720p`  | `720p`<br />`1080p`<br />`4k`  | The resolution of the generated video. `1080p` and `4k` only support 8s duration. |
| `durationSeconds`  | string  | ❌ No     | -       | `4, 6, 8`                      | Length of the generated video in seconds. Must be `8` for 1080p/4k.               |
| `personGeneration` | string  | ❌ No     | -       | `allow_all`<br />`allow_adult` | Controls the generation of people.                                                |
| `enhancePrompt`    | boolean | ❌ No     | `true`  | `true, false`                  | Whether to enhance the prompt for better quality.                                 |

## Scene Comparison

| Feature              | text-to-video | image-to-video | video-to-video |
| -------------------- | :-----------: | :------------: | :------------: |
| `prompt`             |   ✅ Required  |   ✅ Required   |   ✅ Required   |
| `image`              |       ❌       |   ✅ Required   |        ❌       |
| `video`              |       ❌       |        ❌       |   ✅ Required   |
| `aspectRatio`        |       ✅       |        ✅       |        ✅       |
| `resolution`         |       ✅       |        ✅       |        ✅       |
| Audio cues in prompt |       ✅       |        ✅       |        ✅       |

**Notes:**

* **veo-3.1-generate-preview**: Highest quality, suitable for professional content.
* **veo-3.1-fast-generate-preview**: Lower latency, suitable for high-volume tasks.
* **Video retention**: Generated videos are stored for 2 days.
* **Watermarking**: Videos are watermarked using Google SynthID.

## Error Codes

### Common Error Codes

| Error Code | Error Name               | Description                                                                                                       |
| ---------- | ------------------------ | ----------------------------------------------------------------------------------------------------------------- |
| 401        | Unauthorized             | API key is missing or invalid                                                                                     |
| 403        | Forbidden                | Your API key doesn't have permission to access this resource, or insufficient balance for the requested operation |
| 429        | Too Many Requests        | You've exceeded your rate limit                                                                                   |
| 500        | Internal server error    | An internal server error occurred                                                                                 |
| 503        | Content policy violation | Content blocked due to safety concerns (actual status code is 400)                                                |