SeeDance 2.5 - Unifically

Generate videos using ByteDance SeeDance 2.5 with text-to-video, first/last frame, and multimodal reference workflows. It supports image, video, and audio references, synchronized native audio, 4–30 second durations, and 480p or 720p output.

Model

bytedance/seedance-2.5

Request types

Request type	Required inputs	Optional inputs	Notes
Text-to-video	`prompt`	`aspect_ratio`, `duration`, `resolution`, `generate_audio`, `seed`	Do not include reference media URLs
First/last frame	`first_frame_url`, `last_frame_url`	`prompt`, `duration`, `resolution`, `generate_audio`, `seed`	Both frame URLs are required. `aspect_ratio` must be `adaptive` because the output follows the first frame
Multimodal reference	`prompt`, at least one reference URL	`image_urls`, `video_urls`, `audio_urls`, `aspect_ratio`, `duration`, `resolution`, `generate_audio`, `seed`	Reference assets in the prompt as `[Image1]`, `[Video1]`, and `[Audio1]`

Parameters

Parameter	Type	Required	Default	Description
`prompt`	string	Conditional	`""`	Creative description (max 5,000 characters). Required for text-to-video and multimodal reference requests; optional for first/last frame requests. Reference media in array order using `[Image1]`, `[Video1]`, or `[Audio1]`
`resolution`	string	No	`"480p"`	`480p` or `720p`
`duration`	integer	No	`4`	Output duration in whole seconds (4–30)
`aspect_ratio`	string	No	`"adaptive"`	`adaptive`, `1:1`, `3:4`, `4:3`, `9:16`, `16:9`, or `21:9`. Must be `adaptive` for first/last frame requests
`generate_audio`	boolean	No	`true`	Generate synchronized voice, sound effects, and background music with the video
`seed`	integer	No	Random	Seed from `-1` to `2147483647`. Use the same numeric seed for reproducible results; `-1` selects a random seed
`first_frame_url`	string	Conditional	`null`	First frame image URL. Must be provided together with `last_frame_url` and cannot be combined with reference arrays
`last_frame_url`	string	Conditional	`null`	Last frame image URL. Must be provided together with `first_frame_url` and cannot be combined with reference arrays
`image_urls`	string[]	No	`null`	Up to 30 reference image URLs. Reference them as `[Image1]`, `[Image2]`, and so on
`video_urls`	string[]	No	`null`	Up to 10 reference video URLs with a combined duration of up to 30 seconds. Each video must contain at least 409,600 pixels. Reference them as `[Video1]`, `[Video2]`, and so on
`audio_urls`	string[]	No	`null`	Up to 10 reference audio URLs with a combined duration of up to 30 seconds. Audio-only reference requests are supported. Reference them as `[Audio1]`, `[Audio2]`, and so on

The total number of reference assets across images, videos, and audio cannot exceed 50. First/last frame URLs cannot be combined with image_urls, video_urls, or audio_urls.

Example - Text-to-Video

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "bytedance/seedance-2.5",
    "input": {
      "prompt": "A cinematic tracking shot through a bustling night market in the rain, with natural crowd ambience and distant music",
      "aspect_ratio": "16:9",
      "duration": 12,
      "resolution": "720p",
      "generate_audio": true
    }
  }'

Example - First & Last Frame

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "bytedance/seedance-2.5",
    "input": {
      "prompt": "A lone hiker crosses the ridge while morning mist drifts through the valley below",
      "duration": 10,
      "resolution": "720p",
      "first_frame_url": "https://example.com/start.jpg",
      "last_frame_url": "https://example.com/end.jpg"
    }
  }'

Example - Video and Audio References

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "bytedance/seedance-2.5",
    "input": {
      "prompt": "Create a new cinematic sequence inspired by the camera movement in [Video1] and timed to the rhythm of [Audio1]",
      "duration": 15,
      "resolution": "720p",
      "video_urls": [
        "https://example.com/camera-reference.mp4"
      ],
      "audio_urls": [
        "https://example.com/music-reference.mp3"
      ]
    }
  }'

References are numbered independently and in array order: the first image is [Image1], the first video is [Video1], and the first audio clip is [Audio1].

Response

{
  "code": 200,
  "success": true,
  "data": {
    "task_id": "abc123def456",
    "status": "processing"
  }
}

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