Image over video longer than the clip: compose's 300 s ceiling

A Sume compose cannot be longer than its video. Output length comes from the video layer, from video.duration or else the rest of the file after video.source_in, and is capped at 300 seconds. If video.duration runs past the file, it clamps and warns compose_duration_clamped_to_source; the job still succeeds.

This is from the Timeline compose docs, read 2026-10-01. Runway's changelog lists a 5-minute limit for its frame-rate tool; that is a different product, mentioned only because the number matches.

Can the still make the shot longer?

No. The still is held for the whole clip and can never lengthen it. To sequence several pieces, the docs point to Timeline 1.0 instead.

How is the length decided?

The rules, in order of precedence:

Is the clamp an error?

No. It is a warning, listed in the docs as: the job still succeeds. Read warnings on the result rather than treating the code as a failure.

How do I take a section of a longer clip?

Set video.source_in and video.duration.

curl -X POST https://api.sume.com/v1/timeline-1.0/compose \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: compose-window-001" \
  -d '{
    "operation": "stack",
    "image": { "url": "https://media.sume.com/artifacts/artf_demo/poster.png" },
    "video": { "url": "https://media.sume.com/artifacts/artf_demo/interview.mp4", "source_in": 10, "duration": 20 }
  }'