> ## Documentation Index
> Fetch the complete documentation index at: https://docs.unifically.com/llms.txt
> Use this file to discover all available pages before exploring further.

# SeeDance 2.0 Fast

> Speed-optimized video generation with omni-reference support. See supported inputs, parameters, pricing, response fields, and API examples.

Generate videos using ByteDance SeeDance 2.0 Fast — the speed-optimized tier. Supports text-to-video, first/last frame, and omni-reference workflows with image, video, and audio references. Output durations are 4–15 seconds at 480p or 720p.

More on this model: [SeeDance 2.0 Fast API page](https://unifically.com/models/seedance-2.0-fast).

## Model

```
bytedance/seedance-2.0-fast
```

## Request types

| Request type | Required inputs | Optional inputs | Notes |
| - | - | - | - |
| Text-to-video | `prompt` | `aspect_ratio`, `duration`, `resolution`, `generate_audio`, `seed` | No frame or reference URLs |
| First/last frame | At least one of `first_frame_url` or `last_frame_url` | `prompt`, `duration`, `resolution`, `generate_audio`, `seed` | `prompt` optional when a frame URL is set. Provide `first_frame_url`, `last_frame_url`, or both |
| Omni-reference | `prompt`, at least one of `image_urls` or `video_urls` | `video_urls`, `audio_urls`, `duration`, `resolution`, `generate_audio`, `seed` | Reference assets in `prompt` as `@Image1`..`@Image9`, `@Video1`..`@Video3`, `@Audio1`..`@Audio3`. `audio_urls` requires at least one `image_urls` or `video_urls` entry |

## Parameters

| Parameter | Type | Required | Default | Description |
| - | - | - | - | - |
| `prompt` | string | Conditional | `""` | Text prompt (max 5000 chars). **Required** for text-only requests and when `image_urls`, `video_urls`, or `audio_urls` are present. **Optional** when a frame URL is set. Reference assets as `@Image1`..`@Image9`, `@Video1`..`@Video3`, `@Audio1`..`@Audio3` |
| `aspect_ratio` | string | No | `"adaptive"` | `adaptive`, `1:1`, `3:4`, `4:3`, `9:16`, `16:9`, `21:9` |
| `duration` | integer | No | `4` | Output duration in seconds (4–15). Sent to provider as `frames = 24 × seconds + 1` (97–361) |
| `resolution` | string | No | `"480p"` | `480p`, `720p` |
| `generate_audio` | boolean | No | `true` | Whether to generate synchronized audio for the output video |
| `seed` | integer | No | — | Seed for reproducibility. Omit for a random seed. |
| `first_frame_url` | string | No | `null` | First frame image URL. Formats: png, webp, jpeg, gif. Max 30 MB. Dimensions: 300–6000 px (short side). Aspect ratio: 0.4–2.5 |
| `last_frame_url` | string | No | `null` | Last frame image URL. Same format/size constraints as `first_frame_url` |
| `image_urls` | string\[] | No | `null` | Reference image URLs (max 9). Formats: png, webp, jpeg, jpg, gif. Max 30 MB each. Dimensions: 300–6000 px. Aspect ratio: 0.4–2.5. Reference as `@Image1`, `@Image2`, … |
| `video_urls` | string\[] | No | `null` | Reference video URLs (max 3). Formats: mp4, mov. Max 50 MB each. Duration: 2.0–15.2 s per clip, combined total ≤ 15.2 s. Resolution: 480p–1080p. Dimensions: 300–6000 px. Aspect ratio: 0.4–2.5. Reference as `@Video1`, `@Video2`, … |
| `audio_urls` | string\[] | No | `null` | Reference audio URLs (max 3). Requires at least one `image_urls` or `video_urls` entry. Formats: wav, mp3. Max 15 MB each. Duration: 2–15 s per clip, combined total ≤ 15 s. Reference as `@Audio1`, `@Audio2`, … |
| `nsfw_check` | boolean | No | `true` | Check uploaded media inputs for NSFW content |

## Example - Text-to-Video

```bash theme={null}
curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "bytedance/seedance-2.0-fast",
    "input": {
      "prompt": "A drone shot flying over a neon-lit cyberpunk city at night",
      "aspect_ratio": "16:9",
      "duration": 5,
      "resolution": "720p"
    }
  }'
```

## Example - First & Last Frame

```bash theme={null}
curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "bytedance/seedance-2.0-fast",
    "input": {
      "prompt": "Smooth camera pan from left to right",
      "duration": 8,
      "first_frame_url": "https://example.com/start.jpg",
      "last_frame_url": "https://example.com/end.jpg"
    }
  }'
```

## Example - Omni-Reference

```bash theme={null}
curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "bytedance/seedance-2.0-fast",
    "input": {
      "prompt": "Transform the background of @Video1 to match the scenery in @Image1",
      "duration": 8,
      "image_urls": [
        "https://example.com/scenery.jpg"
      ],
      "video_urls": [
        "https://example.com/clip.mp4"
      ]
    }
  }'
```

References are numbered in order: first image = `@Image1`, first video = `@Video1`, first audio = `@Audio1`, etc. Images, videos, and audio are numbered independently.

## Response

```json theme={null}
{
  "code": 200,
  "success": true,
  "data": {
    "task_id": "abc123def456",
    "status": "processing"
  }
}
```

> [!NOTE]
>
> **Volume discounts** are available for almost all models. Reach out at [contact@unifically.com](mailto:contact@unifically.com) to discuss custom pricing.


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