Seedance 2.5 aspect ratios: 9:16 vertical, 21:9 and the rest
Seedance 2.5 on Sume accepts 21:9, 16:9, 4:3, 1:1, 3:4 and 9:16. Set aspect_ratio explicitly; 3:2 is rejected. Ratios, errors and the price effect.
For vertical video, send "aspect_ratio": "9:16" to seedance-2.5. The full list on Sume is 21:9, 16:9, 4:3, 1:1, 3:4 and 9:16, and a ratio outside it, such as 3:2, returns 400 unsupported_capability.
BytePlus's tutorial lists the same six ratios plus adaptive; Sume's seedance-2.5 list on POST /v1/videos does not include adaptive or auto, so pick a fixed ratio.
What happens with a ratio that is not listed?
Pinned models validate resolution, aspect_ratio and duration against the catalog, so the request is refused with a 400 instead of running. Read the list from the catalog first, as in list video models with the API.
Does the ratio change the price?
Only slightly. Reserved amounts for seedance-2.5 at 720p and 10 seconds:
| Aspect ratio | Reserved amount |
|---|---|
| 16:9 | $5.78 |
| 9:16 | $5.78 |
| 1:1 | $5.78 |
| 3:4 | $5.82 |
| 4:3 | $5.82 |
| 21:9 | $5.81 |
Which ratio suits which surface?
Use 9:16 for full-screen vertical placements, 1:1 or 3:4 for feed crops, 16:9 for landscape and 21:9 for cinematic widescreen. Always send aspect_ratio explicitly instead of relying on a default, so the output shape is the one you priced.
Sources
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