Match compose output to the timeline size: no double rescale

Set output.width and output.height on a Sume timeline-1.0/compose request to the size of the timeline you will join the shot into. The default compose output is 1080 by 1920 at the frame rate of the video layer, so a timeline at another size would rescale the shot a second time. Matching the size avoids that second rescale.

This is the sizing advice in Timeline compose (read 2026-10-06), and the timeline defaults are in Timeline 1.0. Both default to 1080 by 1920, so a vertical ad needs no output block at all.

What are the size and rate defaults?

Compose and timeline default to 1080 by 1920. If you omit output.fps on compose, the output uses the video layer's rate, which is the only rate that does not repeat or drop a frame.

What do I send for a 720 by 1280 draft?

If your timeline is a 720 by 1280 draft, ask compose for the same size and a rate of 25 or 30 that matches the clip. An explicit output.fps that differs from the clip's rate resamples it, and the job warns.

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: draft-shot-720-001" \
  -d '{
    "operation": "stack",
    "image": { "url": "https://media.sume.com/artifacts/artf_demo/gift-card.png" },
    "video": { "url": "https://media.sume.com/artifacts/artf_demo/gift-box.mp4" },
    "output": { "width": 720, "height": 1280, "fps": 25 }
  }'

How do I find the clip's rate?

Probe it with video inspect before you set output.fps. Omit the field if you cannot tell, and let compose follow the clip.

• Compose bills $0.02 flat, whatever the size.
• A mute video gives the soft warning compose_video_has_no_audio, and the timeline's spine supplies the audio at assemble time.
• Warnings are not failures: the job still returns a video_url.