QC a 30-second Seedance 2.5 clip with six stills first

Before a client sees a generated 30-second clip, extract six stills with Sume's video frames endpoint at fps: 0.2, which samples at 2.5, 7.5, 12.5, 17.5, 22.5 and 27.5 seconds, and check each against a short list. It is a spot check, not a guarantee, but it catches many visible problems cheaply. The clip must be stored on media.sume.com, so import it first.

Sampling math

The video frames docs say fps expands to mid-bin samples at 0.5/fps, 1.5/fps and so on, capped at 24 frames, with 0 < fps <= 2. At 0.2 fps over 30 seconds that gives six frames. You can instead pass 1 to 24 explicit at values. Exactly one of at or fps is allowed. Output is jpeg by default or png for lossless inspection.

The request

Frame extraction is billed by its compute and runs as an asynchronous job, so poll it. The docs say submit always returns 202 and recommend an idempotency key on REST.

curl -X POST https://api.sume.com/v1/video-frames \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: qc-clip-001" \
  -d '{
    "video_url": "https://media.sume.com/artifacts/artf_demo/clip.mp4",
    "fps": 0.2,
    "format": "png"
  }'

Six questions per still

Ask the same short list of each frame and tick it off.

• Is it the same subject, outfit and proportions as the references?
• Are hands, fingers and faces free of obvious distortion?
• Is any text or logo legible and correct, or clearly absent?
• Does the lighting match the neighbouring stills?
• Is there anything in the frame the brief forbids?
• Does the last still end cleanly, so a caption fits?

What to do when a frame fails

If one still fails, do not guess the cause. Re-run only that idea as a short 480p probe, using the camera test grid approach, or trim the clip with video trim if the fault is at the very end. Regenerating a full 30-second clip is the expensive option, at about $17.33 for 720p on Sume's rate card.