YouTube Shorts max 1080p: downscale a 4K vertical clip with Sume

YouTube's Shorts help page says you can upload Short videos with a maximum resolution of 1080p, so a 2160 by 3840 phone clip is above that. Sume's video trim can re-encode it to 1080 by 1920 in one call: use precision: exact with output: { width: 1080, height: 1920 }, which is a frame-accurate re-encode.

The YouTube statement is from the Shorts help article, read 2026-10-02; it also says Shorts creation tools make videos up to 3 minutes long. The Sume side is the video trim docs.

What exactly does YouTube say about resolution?

One sentence: you can upload Short videos with a maximum resolution of 1080p. The page does not say what YouTube does with a larger file, whether it rejects or downscales it, so this post does not guess. Conforming before upload removes the question.

1080p for a vertical frame is 1080 wide by 1920 tall, the same 9:16 shape Timeline 1.0 uses as its default output.

How does video-trim conform the size?

Trim's optional output takes width, height (each 256 to 2160) and fps (24, 25, 30 or 60), and is available only with precision: exact. Combined with start and duration you can cut and downscale in a single re-encode (libx264, yuv420p, with kept audio remuxed as AAC). Omit output and the clip inherits the source geometry.

Pick the target to match the source's shape, or you will stretch or distort it. A 9:16 source to 1080 by 1920 is clean; a 3:4 source to 1080 by 1920 is not.

What does the call look like?

Cut the whole clip by setting start to 0 and duration to the clip length, or just the range you want. Keep duration at 180 or less for a Short. If you pair output with precision: keyframe, the API refuses with video_trim_output_requires_exact.

The price is the documented $0.02 per job, confirmed live in GET /v1/catalog. There is no model inference; it is worker ffmpeg.

curl -X POST https://api.sume.com/v1/video-trim \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: short-1080p-001" \
  -d '{"video_url":"https://media.sume.com/artifacts/artf_demo/phone4k.mp4",
       "start":0,"duration":55,
       "precision":"exact",
       "output":{"width":1080,"height":1920,"fps":30}}'

How do I confirm it worked?

Read GET /v1/jobs/:id/result: it returns video_url, duration_seconds and optional warnings[]. Then run video inspect with frames: false and check width and height read 1080 and 1920.

Sume does not upload the file. And a downscale loses detail by definition; keep the 4K original if you need it elsewhere, because trim never changes the source.