X video: no open GOP allowed, and what Sume trim exact does

X lists "must not have open GOP" among its video requirements, next to progressive scan, YUV 4:2:0 and a 1:1 pixel aspect ratio. Sume trim has no GOP setting. Its default exact precision is a frame-accurate re-encode with libx264 and yuv420p; keyframe is a stream copy and the docs warn the cut may start a GOP early.

X requirements are from its Media best practices page, read 2026-10-01. Sume facts are from Video trim. Sume does not state that its output has a closed GOP, so verify a file yourself.

What does X require about GOP?

In the Advanced list: "Must not have open GOP", and "Must use progressive scan". The same list requires YUV 4:2:0, a 1:1 pixel aspect ratio and a frame rate of 60 FPS or less.

What does each Sume precision do?

The docs describe the two modes of precision in the trim program table.

Which mode should I use for X?

keyframe copies the source stream as it is, so any GOP structure in the source stays. exact re-encodes, so the output is produced by the worker's ffmpeg, but the docs do not promise a closed GOP, and you cannot send encoder fields: the server refuses codec, crf and similar with ffmpeg_fields_rejected. Prefer exact, then check the result with your own probe before upload.

curl -X POST https://api.sume.com/v1/video-trim \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: x-open-gop-001" \
  -d '{
    "video_url": "https://media.sume.com/artifacts/artf_demo/talk.mp4",
    "start": 0,
    "duration": 30,
    "precision": "exact"
  }'

What else do I check on the output?

Compare the other X rules: AAC LC audio (Sume exact remuxes kept audio as AAC) and the size range in the 1280x1024 conform post. Upload limits and Post-create limits are enforced separately, so test an attach.