Check a video for SynthID in Gemini: 100 MB and 90 s, trim first

To check whether a video came from Google AI, upload it to the Gemini app and ask whether it was made with Google AI. Google's verification post says the check scans for SynthID in both the audio and visual tracks and limits uploads to 100 MB and 90 seconds, so longer videos need to be cut first. Sume's video trim can produce the shorter file.

Facts are from Google's post on verifying AI-generated videos in the Gemini app and its Google I/O 2026 roundup, read on 2026-10-03. This check can only say something about Google's own SynthID mark; it does not detect AI video from other makers.

What the check reports

Google says Gemini reports which segments carry the mark, for example audio at a given second range, rather than a single yes or no. That matters for edited footage, where only part of a clip may be generated. Its I/O post adds that SynthID verification has been used 50 million times and is expanding to Search and Chrome.

Trim a longer clip

Sume's video trim takes a media.sume.com source, a start and exactly one of end or duration, and returns a new MP4. It costs $0.02 per job and does no model inference. Choose windows under 90 seconds, ideally around the segment you want tested, and check each window separately. A re-encode may reduce a watermark's strength, so for a first check, trim with precision: "exact" and compare with a second window.

curl -X POST https://api.sume.com/v1/video-trim \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: synthid-window-001" \
  -d '{
    "video_url": "https://media.sume.com/artifacts/artf_demo/long.mp4",
    "start": 0,
    "duration": 85
  }'

Read the answer carefully

No mark found means no Google SynthID mark was found in that window; it does not prove the clip is human-made. A mark found in only one segment tells you which part was generated. Download the file size before upload: a high-bitrate 80 second clip can still exceed 100 MB, in which case trim shorter.