---
title: "Auto Subtitle"
description: "Auto Subtitle transcribes a clip and burns word-timed captions into it. It is the only caption model that also returns word-level timings and a transcript."
url: https://docs.roasos.com/models/captions/auto-subtitle
---

# Auto Subtitle

<Callout>
  Family 

  `captions`

   · model 

  `auto-subtitle`

   · catalog 

  `model-catalog@2026-10-06.v5`

   · pricing 

  `customer-pricing@2026-11-05.v15`

  .
</Callout>

## Endpoint

```http
POST https://api.roasos.com/v1/captions/auto-subtitle
```

Send your API key as a bearer token. The key needs the scope `api:write`. Every paid request also needs an `Idempotency-Key` header.

The envelope fields `quote_only`, `quote_id`, `webhook_url` and `wait_timeout_seconds` behave the same on each model endpoint. Refer to [Jobs](/concepts/jobs) and [Quotes and credits](/concepts/quotes-and-credits).

## Good at

Caption an ad in the punchy word-by-word style, and get the timings back so you can edit against them. Use this one when you will work with the words later; use VEED Subtitles when the render is the deliverable.

The price is $0.03 for each minute of the source clip, rounded up. There are no multipliers. The source must be 480 seconds or shorter.

## Pricing

The unit is one **source\_minute**. Pricing key: `auto-subtitle`.

| Request       | Credits |
| ------------- | ------- |
| `30s_source`  | 1       |
| `60s_source`  | 1       |
| `120s_source` | 1       |

The credits come from the roasOS pricing table. No other field changes the price. To get the exact price of your request, send it with `quote_only: true` first.

## Modes

* `subtitle`

Provider endpoints: `fal-ai/workflow-utilities/auto-subtitle`.

## Request fields

| Field                  | Type    | Required | Default | Rule                                                                                                                                      |
| ---------------------- | ------- | -------- | ------- | ----------------------------------------------------------------------------------------------------------------------------------------- |
| `audio_url`            | string  | no       | —       | https URL; ≤ 4,096 characters                                                                                                             |
| `background_color`     | enum    | no       | —       | `white`, `black`, `red`, `green`, `blue`, `yellow`, `orange`, `purple`, `pink`, `brown`, `gray`, `cyan`, `magenta`, `none`, `transparent` |
| `enable_animation`     | boolean | no       | —       | —                                                                                                                                         |
| `font_color`           | enum    | no       | —       | `white`, `black`, `red`, `green`, `blue`, `yellow`, `orange`, `purple`, `pink`, `brown`, `gray`, `cyan`, `magenta`                        |
| `font_name`            | string  | no       | —       | ≥ 1 character; ≤ 64 characters                                                                                                            |
| `font_size`            | integer | no       | —       | 20–150                                                                                                                                    |
| `font_weight`          | enum    | no       | —       | `normal`, `bold`, `black`                                                                                                                 |
| `language`             | string  | no       | —       | ≥ 2 characters; ≤ 35 characters                                                                                                           |
| `position`             | enum    | no       | —       | `top`, `center`, `bottom`                                                                                                                 |
| `quote_id`             | string  | no       | —       | UUID                                                                                                                                      |
| `quote_only`           | boolean | no       | `false` | —                                                                                                                                         |
| `stroke_color`         | enum    | no       | —       | `white`, `black`, `red`, `green`, `blue`, `yellow`, `orange`, `purple`, `pink`, `brown`, `gray`, `cyan`, `magenta`                        |
| `stroke_width`         | integer | no       | —       | 0–10                                                                                                                                      |
| `video_url`            | string  | no       | —       | https URL; ≤ 4,096 characters                                                                                                             |
| `wait_timeout_seconds` | integer | no       | `0`     | 0–60                                                                                                                                      |
| `webhook_url`          | string  | no       | —       | https URL; ≤ 4,096 characters                                                                                                             |
| `words_per_subtitle`   | integer | no       | —       | 1–12                                                                                                                                      |
| `y_offset`             | integer | no       | —       | -200–200                                                                                                                                  |

The schema is strict. A field that is not in this table gets `400 unsupported_option`. The field names are the roasOS role names. One role has one name in every family.

## Media

This endpoint accepts these media roles:

* `video_url` — the source video
* `audio_url` — the driving audio track

| Role        | Items | Maximum size | Content types | Duration |
| ----------- | ----- | ------------ | ------------- | -------- |
| `video_url` | ≤ 1   | 100 MB       | `video/mp4`   | 0–480 s  |

Every other role is refused: `avatar_id`, `elements`, `product_id`, `product_images`, `references`, `reference_images`, `image_url`, `end_image_url`, `scene_id`, `scene_image`, `video_urls`, `audio_urls`, `voice_id`. A refused role gets `400 unsupported_option`.

<Callout>
  Each media URL must be an immutable object on 

  `https://cdn.roasos.com`

   that your workspace owns. Any other URL gets 

  `400 reference_media_not_workspace_owned`

  . Refer to 

  [Reference media and uploads](/concepts/reference-media)

   to learn how to put a file there.
</Callout>

## Prompt

None. This model takes no prompt.

Every styling control is optional and none of them changes the price. `words_per_subtitle` is the one that changes the feel most: 1 for single-word display, 2 to 3 for short phrases, 8 to 12 for full sentences.

## Not exposed

These catalog entries describe omitted inputs, pinned values and source constraints. They do not imply that the provider accepts every listed field.

* `background_opacity` — not accepted by this public endpoint.
* `highlight_color` — not accepted by this public endpoint.

## Result

The result kind is `video`. Always present: `url`.

```json
{
  "data": {
    "id": "gen_…",
    "kind": "video",
    "model": "auto-subtitle",
    "status": "completed",
    "result": {
      "url": "https://cdn.roasos.com/workspaces/ws_01/result"
    }
  }
}
```

The files are immutable objects on `https://cdn.roasos.com`. A result URL is a valid media input for your next request.

## Example

The three steps are always the same: quote, run, poll.

<CodeBlockTabs defaultValue="cURL">
  <CodeBlockTabsList>
    <CodeBlockTabsTrigger value="cURL">
      cURL
    </CodeBlockTabsTrigger>

    <CodeBlockTabsTrigger value="JavaScript">
      JavaScript
    </CodeBlockTabsTrigger>

    <CodeBlockTabsTrigger value="Python">
      Python
    </CodeBlockTabsTrigger>
  </CodeBlockTabsList>

  <CodeBlockTab value="cURL">
    ```bash
    # 1. Quote. Nothing is spent.
    curl -X POST https://api.roasos.com/v1/captions/auto-subtitle \
      -H "Authorization: Bearer roasos_sk_live_..." \
      -H "Idempotency-Key: 0f1c9e2a-auto-subtitle-0001" \
      -H "Content-Type: application/json" \
      -d '{"quote_only":true,"video_url":"https://cdn.roasos.com/workspaces/ws_01/uploads/video_url.mp4"}'
    # 200 { "data": { "kind": "quote", "quote_id": "q_7Hk...", "credits": 1, "expires_at": "...",
    #        "confirmation": { "model": "auto-subtitle", "example": "30s_source" } } }

    # 2. Run. Same body, same Idempotency-Key, quote_id in place of quote_only.
    curl -X POST https://api.roasos.com/v1/captions/auto-subtitle \
      -H "Authorization: Bearer roasos_sk_live_..." \
      -H "Idempotency-Key: 0f1c9e2a-auto-subtitle-0001" \
      -H "Content-Type: application/json" \
      -d '{"quote_id":"q_7Hk...","video_url":"https://cdn.roasos.com/workspaces/ws_01/uploads/video_url.mp4"}'
    # 201 { "data": { "id": "gen_...", "status": "queued", "credits_reserved": 1 } }

    # 3. Poll, then read the result.
    curl https://api.roasos.com/v1/jobs/gen_.../status -H "Authorization: Bearer roasos_sk_live_..."
    curl https://api.roasos.com/v1/jobs/gen_.../result -H "Authorization: Bearer roasos_sk_live_..."
    ```
  </CodeBlockTab>

  <CodeBlockTab value="JavaScript">
    ```javascript
    const key = process.env.ROASOS_API_KEY;
    const url = "https://api.roasos.com/v1/captions/auto-subtitle";
    const idempotencyKey = "0f1c9e2a-auto-subtitle-0001";
    const input = {
      "video_url": "https://cdn.roasos.com/workspaces/ws_01/uploads/video_url.mp4"
    };

    const post = (payload) =>
      fetch(url, {
        method: "POST",
        headers: {
          Authorization: `Bearer ${key}`,
          "Idempotency-Key": idempotencyKey,
          "Content-Type": "application/json",
        },
        body: JSON.stringify(payload),
      }).then((response) => response.json());

    // 1. Quote. Nothing is spent.
    const quote = await post({ quote_only: true, ...input });
    console.log(quote.data.credits);

    // 2. Run.
    const job = await post({ quote_id: quote.data.quote_id, ...input });

    // 3. Poll, then read the result.
    let status = "queued";
    while (status !== "completed" && status !== "failed" && status !== "canceled") {
      await new Promise((done) => setTimeout(done, 3000));
      const poll = await fetch(`${url.split("/v1")[0]}/v1/jobs/${job.data.id}/status`, {
        headers: { Authorization: `Bearer ${key}` },
      }).then((response) => response.json());
      status = poll.data.status;
    }

    const result = await fetch(`${url.split("/v1")[0]}/v1/jobs/${job.data.id}/result`, {
      headers: { Authorization: `Bearer ${key}` },
    }).then((response) => response.json());
    console.log(result.data.result);
    ```
  </CodeBlockTab>

  <CodeBlockTab value="Python">
    ```python
    import os, time, requests

    key = os.environ["ROASOS_API_KEY"]
    url = "https://api.roasos.com/v1/captions/auto-subtitle"
    headers = {
        "Authorization": f"Bearer {key}",
        "Idempotency-Key": "0f1c9e2a-auto-subtitle-0001",
    }
    payload = {
        "video_url": "https://cdn.roasos.com/workspaces/ws_01/uploads/video_url.mp4"
    }

    # 1. Quote. Nothing is spent.
    quote = requests.post(url, headers=headers, json={"quote_only": True, **payload}).json()
    print(quote["data"]["credits"])

    # 2. Run.
    job = requests.post(url, headers=headers, json={"quote_id": quote["data"]["quote_id"], **payload}).json()
    job_id = job["data"]["id"]

    # 3. Poll, then read the result.
    jobs = "https://api.roasos.com/v1/jobs"
    status = "queued"
    while status not in ("completed", "failed", "canceled"):
        time.sleep(3)
        status = requests.get(f"{jobs}/{job_id}/status", headers=headers).json()["data"]["status"]

    result = requests.get(f"{jobs}/{job_id}/result", headers=headers).json()
    print(result["data"]["result"])
    ```
  </CodeBlockTab>
</CodeBlockTabs>

## Today

The endpoint is `POST /v1/captions/auto-subtitle`.

It is live.

## See also

* [`llms.txt` for this model](https://docs.roasos.com/models/captions/auto-subtitle/llms.txt) — the same facts as one plain-text file for an agent.
* `GET https://api.roasos.com/v1/catalog/auto-subtitle` — the machine-readable form: enums, defaults, limits and prices. Refer to the [API reference](/api-reference/overview).
* [Jobs](/concepts/jobs) — how to poll a job and read its result.
* Provider endpoints: `fal-ai/workflow-utilities/auto-subtitle`.