Threads video aspect ratio up to 10:1 and 1920 px: timeline output

Threads accepts video aspect ratios from 0.01:1 to 10:1, recommends 9:16, and lists a maximum of 1920 pixels horizontal. The Sume timeline default of 1080 by 1920 is exactly 9:16, so the default render needs no change, and output.width and output.height let you pick another size.

How do the numbers line up?

The Sume range is 256 to 2160 on each side, so keep your own values inside both ranges.

How do I request a size?

This render sets the size explicitly. The audio spine here is a Sume-hosted file, and every video URL must already be in your workspace after a media import.

curl -X POST https://api.sume.com/v1/timeline-1.0/render \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: threads-size-001" \
  -d '{"audio": {"url": "https://media.sume.com/artifacts/artf_demo/voice.wav", "duration_seconds": 24}, "video": [{"source_url": "https://media.sume.com/artifacts/artf_demo/intro.mp4", "start": 0, "duration": 24}], "output": {"width": 1080, "height": 1920}}'

Which limit is easy to miss?

The Threads page says 1920 pixels horizontal, and does not say which side that means for a vertical file. Keep the long side at or below 1920 to be safe, which 1080 by 1920 does, and avoid 2160 sides on this platform.