Day to night video with AI: edit, generate, or grade

To turn a day video into night with AI, describe the change in a video-to-video (edit) prompt, such as “Make this scene night, with the street lights on. Keep everything else the same.” For a clip that turns from day into night on screen, generate one with a daytime still as its first frame and a night version of that still as its last. A darker, cooler color grade is the classic day-for-night route, with no AI.

The steps below use Sume: the edit is the video-to-video mode of gemini-omni-flash-1.1, and the grade is a Video filter job. Facts come from the Video Router, Video generation, Image API, and Video filter docs, the Sume API reference, and Sume's API code, read on 2026-09-28.

How do I make a daytime video look like night?

Send the clip's public HTTPS URL as video_url to POST /v1/video-router/generate with model: "gemini-omni-flash-1.1", currently the only model with this edit, and describe the night in prompt. Edit a video with a prompt has the full request and how to fetch the result.

Say what night looks like in this shot, then what stays. The docs don't promise what else the edit changes, or whether it keeps the source's length, framing, or sound, so compare the result with the original:

• A street: “Make this scene night, with the street lights and shop windows lit. Keep the people and the traffic the same.”
• A house: “Turn this into a clear night with a dark blue sky and warm light in the windows. Keep the house and the camera move the same.”
• Weather is worded the same way, with no promise it works: “Make it snow heavily. Keep everything else the same.”

How do I make a clip that turns from day to night?

Give a video model both ends of the change. The clip opens on your daytime still and ends on a night version of it; the change in between is a new generated shot, not your original footage. Before-and-after video generator API uses the same pattern.

• Make the night still with an image edit: the day photo in input_references, a prompt such as “the same scene at night, street lights on”, and aspect_ratio: "auto" to match the reference.
• Host both stills at public HTTPS URLs. The Image API returns signed links, and video requests refuse signed URLs.
• Send the day still as first_frame and the night still as last_frame. Today every video model except grok-imagine-video-1.5 takes a last frame, and in current code a last frame without a first is refused.

curl -X POST https://api.sume.com/v1/videos \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: day-to-night-001" \
  -d '{
    "model": "seedance-2",
    "prompt": "Time passes from late afternoon to night; the sky darkens and the street lights come on. Static camera.",
    "frame_images": [
      { "type": "image_url", "image_url": { "url": "https://example.com/street-day.png" }, "frame_type": "first_frame" },
      { "type": "image_url", "image_url": { "url": "https://example.com/street-night.png" }, "frame_type": "last_frame" }
    ],
    "resolution": "720p",
    "duration": 8
  }'

Can I do day for night without AI?

Yes. Day for night is a darker, cooler grade, and one Video filter job can do both to a clip that is already your workspace's media.sume.com file, such as an earlier Sume job's output. Darken it with the dim op, as How to brighten a dark video shows. Cool it with colortemperature, one of the color filters Video filter allows today, which the FFmpeg filters documentation says simulates variations in ambient color temperature; How to color correct a video covers its settings. A grade only shifts tones, so the sky stays a day sky and no lights come on.

Which way should I use?

Edit when the footage must be yours, generate when you want the change to happen on screen, and grade when the clip only needs to look darker:

How much does it cost?

The edit is billed per second of output, by resolution, at the provider's list price × 1.25: $0.125 a second at the default 720p, plus a 5.5% agent fee by default. A day-to-night clip is priced like any other clip from its model, as listed in How much does an AI video cost?, plus the image edit for the night still. A filter job is billed per encode; the docs say to confirm the rate in GET /v1/catalog.