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-reference-to-video",
  "prompt": "Keep the same motion style as <<<video_1>>> and replace the background with a snowy scene",
  "video_urls": [
    "https://example.com/reference.mp4"
  ],
  "duration": 5,
  "aspect_ratio": "16:9",
  "quality": "720p"
}
'

{
  "created": 1757169743,
  "id": "task-unified-1757169743-7cvnl5zw",
  "model": "kling-v4-flash-reference-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": 42.84,
    "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-reference-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 Reference to Video

Kling-4.0 Flash Reference to Video (kling-v4-flash-reference-to-video) generates new videos from reference images and videos
Reference videos provide feature references (not direct editing) and can be combined with text and reference images
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
Reference images	Up to `10`	Up to `10`
Reference videos	Up to `5` clips, no more than `20` seconds in total	Up to `5` clips, no more than `30` seconds in total

The total reference-video duration and the output duration have separate limits. Shortening the output does not increase the input limit. For longer reference videos, 1080p output, or output longer than 20 seconds, use Kling 4.0 Reference to Video.

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-reference-to-video",
  "prompt": "Keep the same motion style as <<<video_1>>> and replace the background with a snowy scene",
  "video_urls": [
    "https://example.com/reference.mp4"
  ],
  "duration": 5,
  "aspect_ratio": "16:9",
  "quality": "720p"
}
'

{
  "created": 1757169743,
  "id": "task-unified-1757169743-7cvnl5zw",
  "model": "kling-v4-flash-reference-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": 42.84,
    "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-reference-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-reference-to-video

required

Video generation model name

Available options:

kling-v4-flash-reference-to-video

Example:

"kling-v4-flash-reference-to-video"

prompt

string

required

Text prompt, up to 2500 characters

Reference syntax: Use <<<xxx>>> in the prompt to reference images and videos, for example: The person from <<<image_1>>> walks down the street following the camera movement in <<<video_1>>>

Maximum string length: 2500

Example:

"The person from <<<image_1>>> walks down the street following the camera movement in <<<video_1>>>"

video_urls

string<uri>[]

Reference video URL array, up to 5 clips, corresponding in order to <<<video_1>>>, <<<video_2>>>, etc. in the prompt

Video requirements:

Formats: MP4 / MOV
Size: ≤ 200MB per clip
Duration: ≥ 3 seconds per clip, ≤ 20 seconds in total
Dimensions: width and height from 720px to 2160px
Frame rate: 24fps to 60fps
Video URLs must be directly accessible by the server

Maximum array length: 5

Example:

["https://example.com/reference.mp4"]

image_urls

string<uri>[]

Reference image URL array (style, scene, or subject references), corresponding in order to <<<image_1>>>, <<<image_2>>>, etc. in the prompt

Constraints: Up to 10 images Note: Image URLs must be directly accessible by the server or trigger a direct download when accessed

Maximum array length: 10

Example:

["https://example.com/character.jpg"]

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

aspect_ratio

enum<string>

default:16:9

Video aspect ratio

Options:

16:9: Landscape
9:16: Portrait
1:1: Square
21:9: Ultrawide

Available options:

16:9,

9:16,

1:1,

21:9

Example:

"16:9"

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-reference-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 Reference to Video

Choosing between Flash and Kling 4.0

Authorizations

All APIs require Bearer Token authentication

Body

Response