Mixed real and AI footage: what Gemini's SynthID check reports

If you cut Gemini Omni clips together with real footage, Google's Gemini verification reports which segments carry SynthID rather than labeling the whole file. Google's post gives audio at a specific second range as an example of the output, so a mixed edit should show marks only where the generated clips sit.

Facts come from Google's Gemini app verification post, the Gemini API Omni docs and DeepMind's Omni page, read on 2026-10-03. Google says all Omni videos carry SynthID; DeepMind's page adds C2PA metadata.

Why this matters for editors

A newsroom or brand team may need to say which parts of a piece are generated. Segment reporting supports that. It also means the order and timing of your edit are your own record: keep a note of which seconds are generated, so you can compare to what the check reports.

Build a test edit on Sume

Timeline 1.0 joins ordered clips on one audio spine and returns a single MP4. Put a generated 8 second Omni clip between two real clips, render, and upload the result to Gemini. The timeline docs price a render at $0.10 per output minute rounded up, so a one minute test costs $0.10. Slot start times are explicit, which gives you the seconds log for free.

curl -X POST https://api.sume.com/v1/timeline-1.0/render \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: mixed-synthid-test-001" \
  -d '{
    "audio": { "mode": "silence", "duration_seconds": 24 },
    "video": [
      { "source_url": "https://media.sume.com/artifacts/artf_demo/real-a.mp4", "start": 0, "duration": 8 },
      { "source_url": "https://media.sume.com/artifacts/artf_demo/omni.mp4", "start": 8, "duration": 8 },
      { "source_url": "https://media.sume.com/artifacts/artf_demo/real-b.mp4", "start": 16, "duration": 8 }
    ]
  }'

Read the result

Expect the check to point at the middle window. If it also flags the outer windows or misses the middle, record that and try a version with the original Omni audio. Do not publish a claim about detection reliability from one run; the Timeline docs cover the render options.