curl --request POST \
  --url https://api.evolink.ai/v1/videos/generations \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "model": "kling-v4-flash-image-to-video",
  "prompt": "The person in the image slowly turns their head and smiles",
  "image_start": "https://example.com/portrait.jpg",
  "duration": 5,
  "quality": "720p"
}
'

{
  "created": 1757169743,
  "id": "task-unified-1757169743-7cvnl5zw",
  "model": "kling-v4-flash-image-to-video",
  "object": "video.generation.task",
  "progress": 0,
  "status": "pending",
  "task_info": {
    "can_cancel": false,
    "estimated_time": 300,
    "video_duration": 5
  },
  "type": "video",
  "usage": {
    "billing_rule": "per_second",
    "credits_reserved": 31.96,
    "user_group": "default"
  }
}

{
  "error": {
    "code": "invalid_request",
    "message": "Invalid request parameters",
    "type": "invalid_request_error"
  }
}

{
  "error": {
    "code": "unauthorized",
    "message": "Invalid or expired token",
    "type": "authentication_error"
  }
}

{
  "error": {
    "code": "insufficient_quota",
    "message": "Insufficient quota. Please top up your account.",
    "type": "insufficient_quota"
  }
}

{
  "error": {
    "code": "model_access_denied",
    "message": "Token does not have access to model: kling-v4-flash-image-to-video",
    "type": "invalid_request_error"
  }
}

{
  "error": {
    "code": "rate_limit_exceeded",
    "message": "Too many requests, please try again later",
    "type": "rate_limit_error"
  }
}

{
  "error": {
    "code": "internal_error",
    "message": "Internal server error",
    "type": "api_error"
  }
}

Kling-4.0-Flash

Kling-4.0-Flash Image to Video

Kling-4.0 Flash Image to Video (kling-v4-flash-image-to-video) generates videos from images
Supports only the first frame; last and intermediate frames are not supported
The aspect ratio is determined by the first-frame image, aspect_ratio is not accepted
Only 720p is supported, with a duration of 3–20 seconds
Asynchronous processing mode, use the returned task ID to query status
Generated video links are valid for 24 hours, please save them promptly

Choosing between Flash and Kling 4.0

Flash is designed for frequent creation and rapid creative iteration, focusing on generation speed and cost efficiency for short 720p videos. The comparison below covers the capabilities currently supported by the EvoLink API.

Feature	Kling 4.0 Flash	Kling 4.0
Output resolution	`720p`	`720p`, `1080p`
Output duration	`3`–`20` seconds	`3`–`30` seconds
Frame control	First frame only: `image_start`	First frame, optional last frame `image_end`, and up to `8` intermediate frames in `keyframes`

For first-to-last-frame transitions, intermediate keyframe control, 1080p output, or videos longer than 20 seconds, use Kling 4.0 Image to Video. Flash accepts only the first frame; do not pass image_end or keyframes.

Flash uses separate model IDs. When migrating, check model, quality, and duration. Actual charges depend on the current price of the selected Flash model and the task’s final billing.

POST

videos

generations

curl --request POST \
  --url https://api.evolink.ai/v1/videos/generations \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "model": "kling-v4-flash-image-to-video",
  "prompt": "The person in the image slowly turns their head and smiles",
  "image_start": "https://example.com/portrait.jpg",
  "duration": 5,
  "quality": "720p"
}
'

{
  "created": 1757169743,
  "id": "task-unified-1757169743-7cvnl5zw",
  "model": "kling-v4-flash-image-to-video",
  "object": "video.generation.task",
  "progress": 0,
  "status": "pending",
  "task_info": {
    "can_cancel": false,
    "estimated_time": 300,
    "video_duration": 5
  },
  "type": "video",
  "usage": {
    "billing_rule": "per_second",
    "credits_reserved": 31.96,
    "user_group": "default"
  }
}

{
  "error": {
    "code": "invalid_request",
    "message": "Invalid request parameters",
    "type": "invalid_request_error"
  }
}

{
  "error": {
    "code": "unauthorized",
    "message": "Invalid or expired token",
    "type": "authentication_error"
  }
}

{
  "error": {
    "code": "insufficient_quota",
    "message": "Insufficient quota. Please top up your account.",
    "type": "insufficient_quota"
  }
}

{
  "error": {
    "code": "model_access_denied",
    "message": "Token does not have access to model: kling-v4-flash-image-to-video",
    "type": "invalid_request_error"
  }
}

{
  "error": {
    "code": "rate_limit_exceeded",
    "message": "Too many requests, please try again later",
    "type": "rate_limit_error"
  }
}

{
  "error": {
    "code": "internal_error",
    "message": "Internal server error",
    "type": "api_error"
  }
}

Authorizations

Authorization

string

header

required

All APIs require Bearer Token authentication

Get API Key:

Visit API Key Management Page to get your API Key

Add to request header:

Authorization: Bearer YOUR_API_KEY

Body

application/json

model

enum<string>

default:kling-v4-flash-image-to-video

required

Video generation model name

Available options:

kling-v4-flash-image-to-video

Example:

"kling-v4-flash-image-to-video"

image_start

string<uri>

required

First frame image URL for image-to-video generation (required)

Note:

Image size: up to 10MB
Supported formats: .jpg, .jpeg, .png
Image dimensions: width and height >= 300px, aspect ratio between 1:2.5 and 2.5:1
Image URL must be directly accessible by the server or trigger a direct download when accessed

Example:

"https://example.com/portrait.jpg"

prompt

string

required

Text prompt describing the video to generate

Note:

Maximum 2500 characters

Maximum string length: 2500

Example:

"The person in the image slowly turns their head and smiles"

duration

integer

default:5

Video duration in seconds. Defaults to 5 seconds

Range:

Integer from 3 to 20

Required range: 3 <= x <= 20

Example:

5

quality

enum<string>

default:720p

Resolution tier

Options:

Only 720p is supported

Available options:

720p

Example:

"720p"

callback_url

string<uri>

HTTPS callback URL for task completion

Callback Timing:

Triggered when task is completed, failed, or cancelled
Sent after billing confirmation

Security Restrictions:

HTTPS protocol only
Internal IP addresses are prohibited (127.0.0.1, 10.x.x.x, 172.16-31.x.x, 192.168.x.x, etc.)
URL length must not exceed 2048 characters

Callback Mechanism:

Timeout: 10 seconds
Maximum 3 retries after failure (at 1/2/4 seconds after failure)
Callback response format is consistent with task query API
2xx status code is considered successful, other codes trigger retry

Example:

"https://your-domain.com/webhooks/video-task-completed"

Response

Video generation task created successfully

created

integer

Task creation timestamp

Example:

1757169743

string

Task ID

Example:

"task-unified-1757169743-7cvnl5zw"

model

string

Actual model name used

Example:

"kling-v4-flash-image-to-video"

object

enum<string>

Task type

Available options:

video.generation.task

progress

integer

Task progress percentage (0-100)

Required range: 0 <= x <= 100

Example:

0

status

enum<string>

Task status

Available options:

pending,

processing,

completed,

failed

Example:

"pending"

task_info

object

Video task details

Show child attributes

type

enum<string>

Task output type

Available options:

text,

image,

audio,

video

Example:

"video"

usage

object

Usage and billing information

Show child attributes

Image Series

Video Series

Audio Series

Text Series

Account Management

Task Management

File Management

Kling-4.0-Flash Image to Video

Choosing between Flash and Kling 4.0

Authorizations

All APIs require Bearer Token authentication

Body

Response