# Music Bed (assembly)

> Music Bed puts one music track under a finished clip. The clip keeps its own sound. The output has the same length as the clip.

Status: roasOS API v1.1. Catalog `model-catalog@2026-10-06.v5`, pricing `customer-pricing@2026-11-05.v15`. The endpoint `POST /v1/assembly/music-bed` 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/music-bed
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 to add music below a voice. To replace the sound of a clip, use merge-audio-video.

The price is one credit, flat. The length of the clip does not change the price.

## Pricing
Unit: operation. Pricing key: `music-bed`.

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

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

## Modes
- `music-bed`
Provider endpoints: `fal-ai/ffmpeg-api/compose`.

## Request fields
| field | type | required | default | rule |
|---|---|---|---|---|
| `audio_url` | string | yes | — | https URL; ≤ 4,096 characters |
| `quote_id` | string | no | — | UUID |
| `quote_only` | boolean | no | `false` | — |
| `speech_spans` | object[] | no | — | 1–200 items; each `{ start_seconds, end_seconds }` |
| `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
- `audio_url` — the driving audio track

| role | items | max size | content types | duration |
|---|---|---|---|---|
| `audio_url` | ≤ 1 | 15 MB | `audio/mp3`, `audio/mpeg`, `audio/wav`, `audio/wave`, `audio/x-wav` | — |
| `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`, `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.

`speech_spans` sets the times of the voice, in seconds. The music becomes quieter during each span and louder in the gaps. If you do not send `speech_spans`, the music stays at one low level.

Send a music file that is at least as long as the clip. If the music is shorter, the end of the clip has no music.

## Not exposed
The catalog records no pinned or hidden provider field for this model.

## Result
Result kind `video`. Always present: `url`.
```json
{ "data": { "id": "gen_…", "kind": "video", "model": "music-bed", "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/music-bed \
  -H "Authorization: Bearer roasos_sk_live_…" \
  -H "Idempotency-Key: 0f1c9e2a-music-bed-0001" \
  -H "Content-Type: application/json" \
  -d '{"quote_only":true,"audio_url":"https://cdn.roasos.com/workspaces/ws_01/uploads/audio_url.mp3","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": "music-bed", "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/music-bed \
  -H "Authorization: Bearer roasos_sk_live_…" \
  -H "Idempotency-Key: 0f1c9e2a-music-bed-0001" \
  -H "Content-Type: application/json" \
  -d '{"quote_id":"q_7Hk…","audio_url":"https://cdn.roasos.com/workspaces/ws_01/uploads/audio_url.mp3","video_url":"https://cdn.roasos.com/workspaces/ws_01/uploads/video_url.mp4"}'
# → 201 { "data": { "id": "gen_…", "kind": "video", "model": "music-bed", "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/music-bed`.

It is live.

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