# Text Overlay (assembly)

> Text Overlay puts one line of copy on a finished clip. The copy shows as white text in a dark, rounded card. You set the position and the time window. The clip keeps its own sound.

Status: roasOS API v1.1. Catalog `model-catalog@2026-10-06.v5`, pricing `customer-pricing@2026-11-05.v15`. The endpoint `POST /v1/assembly/text-overlay` is live. `POST /v1/generations` has no `assembly` type, so this endpoint is the only path to this model.

## Endpoint
POST https://api.roasos.com/v1/assembly/text-overlay
Auth: Authorization: Bearer roasos_sk_… (scope api:write). Idempotency-Key required. quote_only / quote_id / webhook_url as in https://docs.roasos.com/llms.txt.

## Good at
Use it for copy that the clip does not say: a hook, an offer, a claim or a call to action. Captions show only the spoken words. Use this operation for all other on-screen text.

The price is three credits, flat. The length of the clip does not change the price.

## Pricing
Unit: operation. Pricing key: `text-overlay`.

| request | credits |
|---|---|
| `per_operation` | 3 |

Credits come from the roasOS pricing table (`MODEL_COSTS`) through the catalog. No other field changes the price.

## Modes
- `text-overlay`
Provider endpoints: `fal-ai/workflow-utilities/blend-video`.

## Request fields
| field | type | required | default | rule |
|---|---|---|---|---|
| `end_seconds` | number | no | — | 0–180 |
| `position` | enum | no | `top` | `top`, `center`, `bottom` |
| `quote_id` | string | no | — | UUID |
| `quote_only` | boolean | no | `false` | — |
| `start_seconds` | number | no | `0` | 0–180 |
| `text` | string | yes | — | ≥ 1 character; ≤ 120 characters |
| `video_url` | string | yes | — | https URL; ≤ 4,096 characters |
| `wait_timeout_seconds` | integer | no | `0` | 0–60 |
| `webhook_url` | string | no | — | https URL; ≤ 4,096 characters |

The schema is strict: a field that is not in this table returns `400 unsupported_option`. Field names are the roasOS role names, one name per role across every family.

## Media
- `video_url` — the source video

| role | items | max size | content types | duration |
|---|---|---|---|---|
| `video_url` | ≤ 1 | 100 MB | `video/mp4` | 0–180 s |

- Refused: `avatar_id`, `elements`, `product_id`, `product_images`, `references`, `reference_images`, `image_url`, `end_image_url`, `scene_id`, `scene_image`, `video_urls`, `audio_urls`, `audio_url`, `voice_id`. A refused role returns `400 unsupported_option`.
- Every URL must be an immutable object on `https://cdn.roasos.com/…` that your workspace owns; any other URL is `400 reference_media_not_workspace_owned`. Upload with `POST /v1/uploads` (direct POST of the bytes to `put_url`, or a `source_url` import), then use the returned CDN URL.

## Prompt
None. This operation takes no prompt.

`text` is the exact copy. It is plain text of 120 characters or fewer. Short lines of 3 to 8 words are easiest to read. Emoji are removed, because they can change the colour of the video below them.

`position` is `top`, `center` or `bottom`. The default is `top`. The top position is below the status bar. The bottom position is above the caption and button area of a social feed. Do not put the card on the product or on the face of the speaker.

`start_seconds` and `end_seconds` set when the copy shows. The default window is the full clip. `end_seconds` must be after `start_seconds`. If `start_seconds` is after the end of the clip, the job fails and you get the credits back. To show two lines, for example a hook and then a call to action, run the operation two times. Use the output of the first run as the input of the second run.

Add text after you trim and join clips, and before you add captions. Each step makes the full file again.

## Not exposed
- `blend_mode`: pinned to `grainmerge`.
- `opacity`: pinned to `1`.
- `shortest`: pinned to `true`.

## Result
Result kind `video`. Always present: `url`.
```json
{ "data": { "id": "gen_…", "kind": "video", "model": "text-overlay", "status": "completed", "result": {"url":"https://cdn.roasos.com/workspaces/ws_01/result"} } }
```
Files live on `https://cdn.roasos.com` and are immutable; a result URL can be a media input to the next call. Poll `GET /v1/jobs/{id}/status` → `{ id, status, updated_at }`, then `GET /v1/jobs/{id}/result` (`409 run_not_completed` until the job is `completed`, `failed` or `canceled`). Statuses: `queued → processing → completed | failed | canceled`.

## Example
```bash
# 1. quote — nothing is spent
curl -X POST https://api.roasos.com/v1/assembly/text-overlay \
  -H "Authorization: Bearer roasos_sk_live_…" \
  -H "Idempotency-Key: 0f1c9e2a-text-overlay-0001" \
  -H "Content-Type: application/json" \
  -d '{"quote_only":true,"text":"Two drops, morning and night. That is the whole routine.","video_url":"https://cdn.roasos.com/workspaces/ws_01/uploads/video_url.mp4"}'
# → 200 { "data": { "kind": "quote", "quote_id": "q_7Hk…", "credits": 3, "expires_at": "…", "confirmation": { "model": "text-overlay", "example": "per_operation" } } }

# 2. run — the same body and the same Idempotency-Key, quote_id instead of quote_only
curl -X POST https://api.roasos.com/v1/assembly/text-overlay \
  -H "Authorization: Bearer roasos_sk_live_…" \
  -H "Idempotency-Key: 0f1c9e2a-text-overlay-0001" \
  -H "Content-Type: application/json" \
  -d '{"quote_id":"q_7Hk…","text":"Two drops, morning and night. That is the whole routine.","video_url":"https://cdn.roasos.com/workspaces/ws_01/uploads/video_url.mp4"}'
# → 201 { "data": { "id": "gen_…", "kind": "video", "model": "text-overlay", "status": "queued", "credits_reserved": 3, "links": { "status": "/v1/jobs/gen_…/status", "result": "/v1/jobs/gen_…/result" } } }

# 3. poll
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_…"
```

## Today
The endpoint is `POST /v1/assembly/text-overlay`.

It is live.

## See also
https://docs.roasos.com/models/assembly/text-overlay · https://api.roasos.com/v1/catalog/assembly/text-overlay · fal-ai/workflow-utilities/blend-video