Hedra Character 3 aspect ratios vs Sume Avatar Video ratios

Hedra Character 3 lists seven aspect ratios: 1:1, 4:3, 3:4, 16:9, 9:16, 9:21 and 21:9. Sume Avatar Video supports five of those: 1:1, 3:4, 9:16, 4:3 and 16:9, with 9:16 as the default. The two ultra-tall and ultra-wide ratios, 9:21 and 21:9, are not in Sume's list.

Hedra's list is from its model page and Sume's from the docs, both read 2026-10-01.

Which ratios does each side list?

How do I set the ratio on Sume?

Send aspect_ratio on POST /v1/avatar-1.0/talking-video. If you omit it, the docs give 9:16. The resolution is currently 720p. See Generate avatar video.

What if I need a wider frame than 16:9?

Sume Avatar Video will not produce 21:9. One documented building block is Timeline compose, which takes one still and one video and returns one MP4 with both on screen at once, using operation of stack or overlay. It requires image.url and video.url, both already on media.sume.com. Whether it gives the frame shape you want depends on your layout, so check the output. For other models' ratio ranges see MiniMax H3 aspect ratios.

Which ratio should I pick for social output?

For vertical feeds use 9:16, which is also Sume's default. For square posts use 1:1. The extra Hedra ratios matter only if your placement specifically needs 9:21 or 21:9.