# Seedance 2.0 Fast (video)

> Seedance 2.0 Fast makes cinematic clips of 4 to 15 seconds with synchronized audio from text, a first frame, or image, video and audio references, at low latency and low cost. It is best for social ads, product motion and quick concept tests.

Status: roasOS API v1.1. Catalog `model-catalog@2026-10-06.v5`, pricing `customer-pricing@2026-11-05.v15`. The endpoint `POST /v1/video/seedance-2` is live. `POST /v1/generations` stays for one minor version as a deprecated alias (see "Today").

## Endpoint
POST https://api.roasos.com/v1/video/seedance-2
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
Seedance 2.0 Fast makes one continuous take of up to 15 seconds with sound effects, ambience and lip-synced speech; the audio has no surcharge. It does multi-shot editing and director-level camera control inside one clip, so a beat-by-beat prompt gets cuts. Use it for drafts and for volume, where latency and price matter more than the highest fidelity. Reference mode binds images, videos and audio files to ordinal tags. It does not accept a human face in a reference image, and it takes no `avatar_id`; use Kling 4.0 elements for a locked identity.

## Pricing
Unit: clip. Pricing key: `seedance-2`.

| request | credits |
|---|---|
| `4s_720p` | 12 |
| `10s_720p` | 30 |
| `15s_720p` | 44 |
| `4s_720p_no_audio` | 12 |

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

## Modes
- `text-to-video`
- `image-to-video`
- `reference-to-video`

The worker derives the mode from the media fields of the request.
Provider endpoints: `bytedance/seedance-2.0/fast/image-to-video` · `bytedance/seedance-2.0/fast/reference-to-video` · `bytedance/seedance-2.0/fast/text-to-video`.

## Request fields
| field | type | required | default | rule |
|---|---|---|---|---|
| `aspect_ratio` | enum | no | `16:9` | `9:16`, `1:1`, `3:4`, `4:3`, `16:9`, `21:9`; only in `text-to-video`, `reference-to-video` |
| `audio_urls` | string[] | no | — | ≤ 3 items; only in `reference-to-video` |
| `bitrate_mode` | enum | no | `standard` | `standard`, `high`; only in `reference-to-video` |
| `duration_seconds` | enum | no | `5` | `auto`, `4`, `5`, `6`, `7`, `8`, `9`, `10`, `11`, `12`, `13`, `14`, `15`; required in `reference-to-video` |
| `end_image_url` | string | no | — | https URL; ≤ 4,096 characters; only in `image-to-video` |
| `extend_of_generation_id` | string | no | — | UUID |
| `generate_audio` | boolean | no | `true` | — |
| `image_url` | string | no | — | https URL; ≤ 4,096 characters; only in `image-to-video` |
| `mode` | enum | no | — | `text-to-video`, `image-to-video`, `reference-to-video` |
| `prompt` | string | yes | — | ≥ 1 character; ≤ 10,000 characters |
| `quote_id` | string | no | — | UUID |
| `quote_only` | boolean | no | `false` | — |
| `references` | string[] | no | — | ≤ 9 items; only in `reference-to-video` |
| `resolution` | enum | no | `720p` | `480p`, `720p` |
| `scene_id` | string | no | — | UUID |
| `video_urls` | string[] | no | — | ≤ 3 items; only in `reference-to-video` |
| `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
- `references` — style and appearance references
- `image_url` — first frame (or the single source image)
- `end_image_url` — last frame
- `scene_id` — first frame — a scene this workspace owns
- `video_urls` — reference videos
- `audio_urls` — reference or driving audio

| role | items | max size | content types | duration |
|---|---|---|---|---|
| `audio_urls` | ≤ 3 | 14.3 MB | `audio/mpeg`, `audio/wav` | — |
| `end_image_url` | ≤ 1 | 10 MB | `image/jpeg`, `image/png`, `image/webp` | — |
| `image_url` | ≤ 1 | 10 MB | `image/jpeg`, `image/png`, `image/webp` | — |
| `references` | ≤ 9 | 10 MB | `image/jpeg`, `image/png`, `image/webp` | — |
| `video_urls` | ≤ 3 | 47.7 MB | `video/mp4` | 2–15 s |

- Refused: `avatar_id`, `elements`, `product_id`, `product_images`, `reference_images`, `scene_image`, `video_url`, `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
Limit 10,000 characters including the roasOS route-facts block (`ROUTE-VERIFIED FEATURE FACTS:` with one line for the first frame or the references). Tags: `@Image1`, `@Video1`, `@Audio1`, each once, in order.
- Write the prompt as one continuous progression with plain cause-and-effect motion.
- Order: Subject → Action → Camera → Style/lighting → Constraints. One primary movement per beat.
- Give each beat a start time: `[00:00] … [00:05] …`.
- Put quoted dialogue in the prompt when you want speech: `She says: "…"`. Name the mic source.
- Dialogue pacing: 1–8 words ≈ 4–5 s, 9–15 ≈ 6–8 s, 16–25 ≈ 9–12 s.
- Avoid: cinematic, professional, stunning, 8k, studio, perfect.
- Do not put a face in an image reference; describe the person in words.

## Not exposed
- `bitrate_mode`: pinned to `text-to-video and image-to-video; the field is sent on the reference lane only`.
- `aspect_ratio`: pinned to `auto`.
- `end_user_id`: not accepted by this public endpoint.
- `video_urls`: values not exposed — `MOV containers`.
- `references`: values not exposed — `BMP`, `TIFF`, `GIF`, `HEIC`, `HEIF`.
- `avatar_id`: not accepted by this public endpoint.
- `product_id`: not accepted by this public endpoint.
- `seed`: pinned to `output only`.
- `negative_prompt`: not accepted by this public endpoint.

## Result
Result kind `video`. Always present: `url`.
```json
{ "data": { "id": "gen_…", "kind": "video", "model": "seedance-2", "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/video/seedance-2 \
  -H "Authorization: Bearer roasos_sk_live_…" \
  -H "Idempotency-Key: 0f1c9e2a-seedance-2-0001" \
  -H "Content-Type: application/json" \
  -d '{"quote_only":true,"prompt":"A woman holds the bottle at eye level in a bright kitchen, morning light, static camera."}'
# → 200 { "data": { "kind": "quote", "quote_id": "q_7Hk…", "credits": 12, "expires_at": "…", "confirmation": { "model": "seedance-2", "example": "4s_720p" } } }

# 2. run — the same body and the same Idempotency-Key, quote_id instead of quote_only
curl -X POST https://api.roasos.com/v1/video/seedance-2 \
  -H "Authorization: Bearer roasos_sk_live_…" \
  -H "Idempotency-Key: 0f1c9e2a-seedance-2-0001" \
  -H "Content-Type: application/json" \
  -d '{"quote_id":"q_7Hk…","prompt":"A woman holds the bottle at eye level in a bright kitchen, morning light, static camera."}'
# → 201 { "data": { "id": "gen_…", "kind": "video", "model": "seedance-2", "status": "queued", "credits_reserved": 12, "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
`POST /v1/generations { "type": "video", "model": "seedance-2", "options": { prompt, image, last_frame, reference_images, reference_videos, audio_urls, duration, resolution, aspect_ratio, generate_audio } }`. Contract authority `exact`. Write every ordinal tag yourself: a missing `@Image1`, `@Video1` or `@Audio1` is a 400 on both surfaces. The alias stays one minor version after v1.1 ships.

## See also
https://docs.roasos.com/models/video/seedance-2 · https://api.roasos.com/v1/catalog/video/seedance-2 · bytedance/seedance-2.0/fast/image-to-video · bytedance/seedance-2.0/fast/reference-to-video · bytedance/seedance-2.0/fast/text-to-video