Kling 4.0 Flash

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Models

• kling-4.0-flash — Text-to-video, image-to-video, reference-to-video, and video editing at 720p

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Features

• Fast 720p output: Generate 3–20 second videos at 720p.
• Starting frame: Animate one starting image. Flash does not accept an ending frame.
• Visual references: Guide appearance and movement with reference images, reference videos, and subjects defined by images or a video.
• Video editing: Supply a source video and describe the changes. Editing also accepts reference images, reference videos, and subjects. Omit duration to retain the source video’s duration.
• Aspect ratios: Use 16:9, 9:16, 1:1, 21:9, or auto in text and reference modes.

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Input modes

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Required parameters

• prompt (string): Video instructions, 1–26,000 characters, containing at least one non-whitespace character. Required in every mode except image-to-video, where it is optional.

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Optional parameters

• duration (integer): Output duration from 3 to 20 seconds. Generation defaults to 5. In editing, omit this field to retain the source video’s duration; chargeable output duration is rounded up to whole seconds.
• resolution (string): 720p only. Default: 720p.
• aspect_ratio (string): auto, 16:9, 9:16, 1:1, or 21:9, for text and reference modes. Default: 16:9. In text-to-video, auto is treated as 16:9; in reference mode, auto adapts to the supplied materials. Omit this field in image and editing modes.
• image_urls (array of strings): One starting image.
• video_url (string): Source video for editing. Must last 3–20 seconds.
• reference_image_urls (array of strings): Up to 10 publicly accessible HTTP or HTTPS image URLs.
• reference_video_urls (array of strings): Publicly accessible HTTP or HTTPS video URLs, each lasting 3–20 seconds. Up to 5 in reference mode and up to 4 in editing mode.
• kling_elements (array of objects): Up to 7 subjects. Each subject supplies exactly one of:
  • element_input_urls (array of strings): 2–4 images, with the frontal view first and additional reference views after it.
  • element_input_video_urls (array of strings): Exactly one 3–8 second video. At most 3 subjects may use videos.

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Examples

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Text to Video

{
  "model": "kling-4.0-flash",
  "callback_url": "https://your-domain.com/callback",
  "input": {
    "prompt": "A paper boat drifts through a miniature city at sunset, slow camera push-in",
    "duration": 5,
    "aspect_ratio": "16:9"
  }
}

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Image to Video

{
  "model": "kling-4.0-flash",
  "input": {
    "prompt": "The red panda shakes the snow off its fur and turns toward the camera",
    "image_urls": ["https://example.com/start-frame.png"],
    "duration": 5
  }
}

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Reference Images and Subjects

{
  "model": "kling-4.0-flash",
  "input": {
    "prompt": "@Element1 walks along the cliff path toward the lighthouse in @Image1 at golden hour",
    "reference_image_urls": ["https://example.com/lighthouse.png"],
    "kling_elements": [
      {
        "element_input_urls": [
          "https://example.com/keeper-front.png",
          "https://example.com/keeper-side.png"
        ]
      }
    ],
    "duration": 8,
    "aspect_ratio": "9:16"
  }
}

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Reference Videos

{
  "model": "kling-4.0-flash",
  "input": {
    "prompt": "Follow the camera movement of @Video1 in the snowy mountain scene from @Image1",
    "reference_image_urls": ["https://example.com/mountain.png"],
    "reference_video_urls": ["https://example.com/camera-motion.mp4"],
    "duration": 8,
    "aspect_ratio": "16:9"
  }
}

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Video Editing

{
  "model": "kling-4.0-flash",
  "input": {
    "prompt": "Change the season in @Video1 to spring using @Image1, keeping the motion and camera",
    "video_url": "https://example.com/source.mp4",
    "reference_image_urls": ["https://example.com/spring.png"]
  }
}

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Notes

• In reference mode, the optional starting frame and reference images together cannot exceed 10 images. The number of starting frames, reference images, reference videos, and subjects combined cannot exceed 15. Images inside a subject count as one subject, not as separate materials.
• The source video, reference videos, and video-based subjects must have a combined original duration of at most 20 seconds. Each source or reference video must last 3–20 seconds, and each subject video 3–8 seconds.
• Flash does not support 1080p, ending frames, or multi_prompt. Use Kling 4.0 for these.
• Reference indexes start at 1 and follow the order of the corresponding input array. Use publicly accessible media URLs and omit unused optional fields.

Authorization: Bearer YOUR_API_KEY