Seedance 2.5 480p: ratio 864:496 gives 854x480, Sume uses resolution

On Runway, a Seedance 2.5 request at 480p with ratio 864:496 or 496:864 comes back as standard 854x480 or 480x854 video, not the literal pixel counts. On Sume you never send either number: set resolution: "480p" and an aspect_ratio such as 16:9 or 9:16 on seedance-2.5.

Runway's side is from its Dev API changelog entry for Seedance 2.5 (August 7, 2026); Sume's side is from the video generation docs and video router docs, both read 2026-10-01.

What does Runway say about 864:496?

The changelog says that at 480p, ratios 864:496 and 496:864 deliver standard 854x480 and 480x854 output rather than the literal pixel counts. So if you measure the file, expect 854 by 480 (or the portrait flip), not 864 by 496.

How do I ask for 480p on Sume?

Sume splits the Runway ratio string into two named fields. Resolution is a tier, and aspect ratio comes from a separate list. The docs say each model advertises what it accepts in supported_resolutions and supported_aspect_ratios. For seedance-2.5, the video router docs list 4–30 seconds at 480p, 720p and 1080p.

Why not send size: 854x480?

The docs state that every v1 model reports supported_sizes: null, so size returns 400 unsupported_parameter. Use resolution plus aspect_ratio instead of converting a Runway ratio into a pixel pair. The Sume docs do not state the exact pixel dimensions of a 480p output, so measure a finished file if your pipeline depends on them.

What does the request look like?

A minimal call to the video router, following the field names in the router docs. See also the 480p draft then 1080p workflow.

const res = await fetch("https://api.sume.com/v1/video-router/generate", {
  method: "POST",
  headers: {
    Authorization: "Bearer " + process.env.SUME_API_KEY,
    "Content-Type": "application/json",
    "Idempotency-Key": "seedance-480p-001",
  },
  body: JSON.stringify({
    model: "seedance-2.5",
    prompt: "A slow dolly through a rainy night market",
    resolution: "480p",
    duration: 6,
    aspect_ratio: "16:9",
    mode: "async",
  }),
});
console.log(await res.json());

What should I do next?

Drop any code that parses a Runway ratio into pixels. Read GET /v1/video-router/models for the live capabilities of the id, and send the two fields. The docs say to read capabilities there rather than assume one envelope across models.