Seedance 2.0 aspect ratio auto: can you send it on Sume?

No. fal's Seedance 2.0 pages list auto as an aspect_ratio option, but Sume's seedance-2 advertises six fixed ratios (21:9, 16:9, 4:3, 1:1, 3:4 and 9:16), and its request check refuses a value that is not on the list. Send one of the six.

The fal facts below were read on 2026-09-29. The Sume facts come from the Video generation docs and the API's request checks.

What does fal list for Seedance 2.0 aspect ratio?

fal's fast text-to-video page lists the parameter with a default of auto and seven options. Its main Seedance 2.0 page describes the same idea as an adaptive ratio the model picks from your inputs.

What happens if I send aspect_ratio auto to Sume?

The API checks aspect_ratio against the model's advertised list and returns 400 unsupported_capability with a message such as "seedance-2 does not support aspect_ratio auto." The public list for seedance-2 does not contain auto or adaptive.

curl -X POST https://api.sume.com/v1/videos \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "seedance-2",
    "prompt": "A tram crossing a bridge at dusk",
    "duration": 5,
    "aspect_ratio": "auto"
  }'
# 400 unsupported_capability: seedance-2 does not support aspect_ratio auto.

Which ratio should I send instead?

Pick the ratio by where the clip will play, and pass it every time. Use 9:16 for vertical placements, 16:9 for landscape, 1:1 for square and 21:9 for ultrawide. The list is the one the model advertises, and you can read it live from GET /v1/videos/models instead of hard-coding it.

If your app relies on the model choosing the ratio from an input image, read the image's width and height yourself and map it to the closest listed ratio before you submit.

Does the ratio change what a clip reserves?

It can. Sume's Seedance price estimate uses the token formula (width * height * duration_seconds * 24_fps) / 1024, so the frame size feeds the estimate. Pass aspect_ratio and resolution explicitly so the estimate matches what you meant. The amount that was billed comes back on the job as usage.cost.

How do I read the allowed ratios at runtime?

Call GET /v1/videos/models and read supported_aspect_ratios for the model id you use. Validate the ratio in your own code against that array before you submit, so a wrong value fails in your app with a clear message instead of as a 400 from the API. The same descriptor lists supported_durations and supported_resolutions.

Does the same rule apply to duration auto?

fal also lists duration as auto or an integer from 4 to 15. Sume's docs describe duration as an integer number of seconds, and the model row lists 4 to 15 whole seconds, so send an integer.