Veo 3.1 - Unifically

Generate videos with Google’s Veo 3.1 modes through the unified task API. Veo 3.1 supports text-to-video, first-frame, first-and-last-frame, and reference-to-video workflows.

Models

Mode	Model ID	Character references	Notes
Lite	`google/veo-3.1-lite`	Yes	Balanced default
Fast	`google/veo-3.1-fast`	Yes	Faster generation
Quality	`google/veo-3.1-quality`	No	Higher quality text/image-to-video, but no character references
Lite Relaxed	`google/veo-3.1-lite-relaxed`	Yes	Relaxed queue variant

Parameters

Parameter	Type	Required	Default	Description
`prompt`	string	Yes	-	Main video prompt. Use `@ImageN` or `@CharacterN` to point at a specific reference. Unknown references are left as plain text.
`seed`	integer	No	Random	Seed sent to Veo. If omitted, a seed is generated automatically and returned when available.
`aspect_ratio`	string	No	`"16:9"`	Output orientation. Allowed: `"16:9"`, `"9:16"`.
`duration`	integer	No	`4`	Text/start-frame requests allow `4`, `6`, or `8`. Any `reference_image_urls` or `reference_characters` reference locks duration to `8`.
`start_image_url`	string	No	-	Publicly reachable image URL used as the first frame. Cannot be combined with `reference_image_urls` or `reference_characters`.
`end_image_url`	string	No	-	Publicly reachable image URL used as the final frame. Requires `start_image_url`; cannot be used by itself.
`reference_image_urls`	string[]	No	-	Image references for reference-to-video. Max 3 total expanded image URLs across `reference_image_urls` and character images. Cannot be combined with start/end frame fields.
`reference_characters`	array	No	-	Character references for reference-to-video. Max 3 total expanded image URLs across images and character `image_urls`. Not available on Quality.
`voice`	string	No	-	Request-level Google Flow voice preset ID. Requires at least one image or character reference. See available voices.
`allow_audio_filtered`	boolean	No	`false`	When `true`, the generation runs without audio instead of failing when the audio track is filtered.

First/last-frame mode and reference mode are separate generation modes. Do not combine start_image_url or end_image_url with reference_image_urls or reference_characters.

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": "google/veo-3.1-fast",
    "input": {
      "prompt": "A cinematic shot of a cat walking through a garden",
      "aspect_ratio": "16:9",
      "duration": 4
    }
  }'

First and Last Frame

Use start_image_url and optionally end_image_url to guide the video with first and final frames.

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "google/veo-3.1-fast",
    "input": {
      "prompt": "Camera slowly zooms in",
      "start_image_url": "https://example.com/start.jpg",
      "end_image_url": "https://example.com/end.jpg",
      "aspect_ratio": "16:9",
      "duration": 6
    }
  }'

References and Characters

Use reference_image_urls for image references and reference_characters for character identity consistency. Character references are supported on Lite, Fast, and Lite Relaxed. They are not supported on Quality.

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "google/veo-3.1-fast",
    "input": {
      "prompt": "Make @Character1 walk through a glass city at sunrise, speaking softly to camera.",
      "reference_characters": [
        {
          "image_urls": [
            "https://example.com/ada.png"
          ],
          "name": "Ada",
          "description": "warm, sharp, curious"
        }
      ],
      "duration": 8,
      "aspect_ratio": "9:16"
    }
  }'

Character References

Provide each character as an object with image_urls. Even one-image characters must use an array.

{
  "image_urls": [
    "https://example.com/character-front.png",
    "https://example.com/character-profile.png"
  ],
  "name": "Ada",
  "description": "warm, sharp, curious"
}

Field	Type	Required	Description
`image_urls`	string[]	Yes*	Publicly reachable character image URLs. Use 1-10 images for a character entity. Each URL still consumes a model reference-image slot.
`name`	string	No	Display name for the character.
`description`	string	No	Character notes/personality text.

*image_urls must contain at least one URL.

image_url and plain string character entries are not supported. Use image_urls for every character, including one-image characters.

Prompt References

Token	Refers to
`@Image1`, `@Image2`	Items from `reference_image_urls` only
`@Character1`, `@Character2`	Items from `reference_characters` only. With multiple `image_urls`, the token points to the character item; extra images are identity references

Duration

Mode	What you send	4s	6s	8s
Text-to-video	`prompt` only	Yes	Yes	Yes
First-frame	`prompt` + `start_image_url`	Yes	Yes	Yes
First-and-last-frame	`prompt` + `start_image_url` + `end_image_url`	Yes	Yes	Yes
Reference-to-video	`reference_image_urls` or `reference_characters`	No	No	Yes

Rejected Combinations

Input	Why rejected
`end_image_url` without `start_image_url`	The ending frame needs a starting frame.
`start_image_url`/`end_image_url` with `reference_image_urls` or `reference_characters`	First/last-frame mode and reference mode are separate generation modes.
`reference_characters` on `google/veo-3.1-quality`	Quality does not expose character references.
Any image or character reference with `duration` other than `8`	Veo reference-image generation is 8 seconds only.
More than 3 total expanded image URLs	Veo reference generation limit.
`image_url` on a character	Use `image_urls` instead, even for one image.
Plain string character entries	Character entries must be objects with `image_urls`.
Empty `image_urls`	A character needs at least one image.
More than 10 `image_urls` on one character	Character entity image limit.

Extend

Extend a previously generated video using google/veo-3.1-extend. The aspect ratio is inherited from the source task.

Parameter	Type	Required	Description
`prompt`	string	Yes	Text prompt for the extended content
`task_id`	string	Yes	Task ID of a completed generation
`model`	string	Yes	One of: `lite`, `fast`, `quality`, `lite-relaxed`
`duration`	integer	No	Must be `8`. Default `8`.
`seed`	integer	No	Reproducibility seed

Upscale

Upscale a completed video to a higher resolution using google/veo-3.1-upscale.

Parameter	Type	Required	Description
`task_id`	string	Yes	Task ID of a completed generation
`resolution`	string	Yes	`"1080p"` or `"4k"`

Response

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

​Models

​Parameters

​Text-to-Video

​First and Last Frame

​References and Characters

​Character References

​Prompt References

​Duration

​Rejected Combinations

​Extend

​Upscale

​Response

Models

Parameters

Text-to-Video

First and Last Frame

References and Characters

Character References

Prompt References

Duration

Rejected Combinations

Extend

Upscale

Response