Change the weather in a video with Gemini Omni Flash edit

To change the weather in a clip, send it to Gemini Omni Flash 1.1 as video_url and prompt a single change: "Make it rain heavily. Keep everything else the same." Google's guide recommends simple edit prompts and names this closing phrase; it does not list weather as a tested edit, so run it on your own footage and inspect the result.

Facts here are from Google DeepMind's Omni prompt guide, the Gemini API Omni docs and DeepMind's Omni page (read 2026-10-03), plus Sume's Video Router docs.

What the sources support

Google's pages list editing existing video, swapping characters or objects, and lighting control among Omni capabilities. Weather is not named, so frame it as a prompt to test. The model works on clips of 10 seconds or less, and the output carries a SynthID watermark.

Prompt wording to try

Change one condition at a time: rain, fog, snow or overcast. Add the light that goes with it, since a rainy scene with hard sunlight reads as wrong: "Overcast, flat grey light, wet pavement." Avoid asking for weather and a time-of-day change together in one pass.

Request

Sume's edit mode is chosen by video_url: it cannot be combined with image_url, end_image_url or reference_*_urls, takes no aspect_ratio or duration, and resolution defaults to 720p. Native audio is always on.

curl -X POST https://api.sume.com/v1/video-router/generate \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: weather-rain-001" \
  -d '{
    "model": "gemini-omni-flash-1.1",
    "prompt": "Make it rain heavily with flat grey overcast light and wet pavement. Keep everything else the same.",
    "video_url": "https://media.sume.com/artifacts/artf_demo/source.mp4",
    "resolution": "720p",
    "mode": "async"
  }'

Inspect the result

Pull stills from the source and result at matching timestamps with Video inspect. Check that people, signs and the camera path survived, that shadows match the new light, and that the audio still fits. If it fails, rerun with a more specific description of the weather, not a longer one.