# FFmpeg Merge Videos (assembly)

> Merge Videos joins finished clips end to end, in the order you send them. It is the simplest way to turn a set of shots into one deliverable.

Status: roasOS API v1.1. Catalog `model-catalog@2026-10-06.v5`, pricing `customer-pricing@2026-11-05.v15`. The endpoint `POST /v1/assembly/merge-videos` 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/merge-videos
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
Stitch a batch of generated clips into one ad. Send at least two URLs and at most 12. The output keeps the smallest width and height across the inputs unless you set a frame rate.

Use this rather than Compose when you only need one clip after another with no overlay and no separate audio track.

The price is one credit, flat, whatever the clips are. fal prints `$0 per compute seconds` for this operation; the credit pays for the roasOS door, not for the provider.

## Pricing
Unit: operation. Pricing key: `merge-videos`.

| request | credits |
|---|---|
| `per_operation` | 1 |

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

## Modes
- `merge-videos`
Provider endpoints: `fal-ai/ffmpeg-api/merge-videos`.

## Request fields
| field | type | required | default | rule |
|---|---|---|---|---|
| `quote_id` | string | no | — | UUID |
| `quote_only` | boolean | no | `false` | — |
| `target_fps` | number | no | — | 1–60 |
| `video_urls` | string[] | yes | — | 2–12 items |
| `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_urls` — reference videos

| role | items | max size | content types | duration |
|---|---|---|---|---|
| `video_urls` | ≤ 12 | 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_url`, `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.

Send the clips in the order you want them played. Each clip must appear once: a repeated URL is refused, because on this operation it is almost always a mistake. To play one clip twice, use Compose.

## Not exposed
- `resolution`: not accepted by this public endpoint.
- `resolution_aspect_ratio_video_index`: not accepted by this public endpoint.

## Result
Result kind `video`. Always present: `url`.
```json
{ "data": { "id": "gen_…", "kind": "video", "model": "merge-videos", "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/merge-videos \
  -H "Authorization: Bearer roasos_sk_live_…" \
  -H "Idempotency-Key: 0f1c9e2a-merge-videos-0001" \
  -H "Content-Type: application/json" \
  -d '{"quote_only":true,"video_urls":["https://cdn.roasos.com/workspaces/ws_01/uploads/video_urls-1.mp4"]}'
# → 200 { "data": { "kind": "quote", "quote_id": "q_7Hk…", "credits": 1, "expires_at": "…", "confirmation": { "model": "merge-videos", "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/merge-videos \
  -H "Authorization: Bearer roasos_sk_live_…" \
  -H "Idempotency-Key: 0f1c9e2a-merge-videos-0001" \
  -H "Content-Type: application/json" \
  -d '{"quote_id":"q_7Hk…","video_urls":["https://cdn.roasos.com/workspaces/ws_01/uploads/video_urls-1.mp4"]}'
# → 201 { "data": { "id": "gen_…", "kind": "video", "model": "merge-videos", "status": "queued", "credits_reserved": 1, "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/merge-videos`.

It is live.

## See also
https://docs.roasos.com/models/assembly/merge-videos · https://api.roasos.com/v1/catalog/assembly/merge-videos · fal-ai/ffmpeg-api/merge-videos