LTX 2.5 Fast Image to Video API

POST Base URL: https://api.hiapi.ai /v1/tasks

Image, video, and audio models are called through theUnified Async API POST /v1/tasks endpoint; only the input fields differ (see input parameters below).

Model summary

Model	ltx-2.5-fast/image-to-video
Capability	First frame / first-last frame video + native audio
Resolution	720p / 1080p
Duration	2-20 seconds

Animate a first frame, optionally toward a last frame, into a 2-20 second 720p or 1080p video with native audio. Billed per second.

Production guidance

Calling the API

Match aspect_ratio to the first frame to avoid cropping or padding.
For first/last-frame clips, keep composition and camera position similar for a smooth transition.
Use callback.url for task notifications; read the task object from data in query responses and directly from the callback body.
Artifact URLs expire; copy files you need to keep into persistent storage.

Best suited for

Animate a still

Add motion and camera to product shots, scenery or illustration.

image_urlsprompt

First-to-last transitions

Day to night, closed to open — a natural move between two images.

image_urls

Clips with sound

Ambience and effects generated with the picture.

generate_audio

Request parameters

POST https://api.hiapi.ai/v1/tasks

# Create an async task — returns taskId immediately (generation runs async)
# Replace YOUR_API_KEY with your account API key
curl -X POST "https://api.hiapi.ai/v1/tasks" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "model": "ltx-2.5-fast/image-to-video",
  "input": {
    "prompt": "Waves crash against the rocks below the lighthouse, seagulls glide across the golden sky, the camera slowly pushes in, sound of surf and gulls",
    "image_urls": [
      "https://example.com/first-frame.jpg"
    ],
    "resolution": "720p",
    "duration": 6,
    "aspect_ratio": "16:9",
    "generate_audio": true
  }
}'

import requests, json

# Business params — fields vary by model (see the model page)
payload = json.loads(r'''
{
  "model": "ltx-2.5-fast/image-to-video",
  "input": {
    "prompt": "Waves crash against the rocks below the lighthouse, seagulls glide across the golden sky, the camera slowly pushes in, sound of surf and gulls",
    "image_urls": [
      "https://example.com/first-frame.jpg"
    ],
    "resolution": "720p",
    "duration": 6,
    "aspect_ratio": "16:9",
    "generate_audio": true
  }
}
''')

# Create an async task — returns taskId immediately (generation runs async)
resp = requests.post(
    "https://api.hiapi.ai/v1/tasks",
    headers={"Authorization": "Bearer YOUR_API_KEY", "Content-Type": "application/json"},
    json=payload,
)
print(resp.json())  # Returns { code, message, data: { taskId } }

// Create an async task — returns taskId immediately (generation runs async)
// Replace YOUR_API_KEY with your account API key
const resp = await fetch("https://api.hiapi.ai/v1/tasks", {
  method: "POST",
  headers: {
    "Authorization": "Bearer YOUR_API_KEY",
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
  "model": "ltx-2.5-fast/image-to-video",
  "input": {
    "prompt": "Waves crash against the rocks below the lighthouse, seagulls glide across the golden sky, the camera slowly pushes in, sound of surf and gulls",
    "image_urls": [
      "https://example.com/first-frame.jpg"
    ],
    "resolution": "720p",
    "duration": 6,
    "aspect_ratio": "16:9",
    "generate_audio": true
  }
}),
});
console.log(await resp.json()); // Returns { code, message, data: { taskId } }

model string required

Model ID.

example ltx-2.5-fast/image-to-video

input object required

Image-to-video parameters.

prompt string required

Describe the motion, camera and sound to add; no need to restate the image. Up to 5,000 characters.

image_urls string[] required

1-2 public image URLs starting with http:// or https:// (JPG/PNG/WebP). The first is the first frame; a second one is used as the last frame and the video transitions between them.

resolution enum optional

Output resolution; sets the per-second price.

default 720p enum: 720p1080p

duration enum optional

Length in seconds: 2-6, 8, 10, 12, 14, 16, 18 or 20. Billed per second.

default 6 enum: 234568101214161820

aspect_ratio enum optional

Landscape 16:9 or vertical 9:16.

default 16:9 enum: 16:99:16

generate_audio boolean optional

Generate native audio (ambience, effects, music) with the video. Does not change the price.

default true

callback object optional

Sends a notification when the task succeeds or fails; read the task object from data in query responses and directly from the callback body.

url string required

HTTPS URL that receives task success or failure notifications.

example https://your-domain.com/hiapi/callback

when enum optional

Triggers when the task succeeds or fails.

default final enum: final

Example requests

First frame only

Pass one image.

Request body

{
  "model": "ltx-2.5-fast/image-to-video",
  "input": {
    "prompt": "Waves crash against the rocks below the lighthouse, seagulls glide across the golden sky, the camera slowly pushes in, sound of surf and gulls",
    "image_urls": [
      "https://example.com/first-frame.jpg"
    ]
  }
}

First and last frame

Pass two images; the second is the last frame.

Request body

{
  "model": "ltx-2.5-fast/image-to-video",
  "input": {
    "prompt": "Time passes from day to night, the windows light up, fixed camera",
    "image_urls": [
      "https://example.com/day.jpg",
      "https://example.com/night.jpg"
    ],
    "duration": 5
  }
}

Getting the result

Read data.taskId from the create-task response.
Wait for the callback or query GET /v1/tasks/:id; polling puts the task under data.
When status=success, read the video URL from output type=video; a callback reads output directly.

FAQ

Is a last frame required?

No. One image is used as the first frame; with two, the second becomes the last frame.

What sets the output aspect ratio?

aspect_ratio (16:9 or 9:16); match it to the first frame.

Is it cheaper with generate_audio off?

No. Price depends only on resolution and duration.

Which resolutions are supported?

720p (default) and 1080p.