YouTube image posts in Shorts: up to 10 images, 16 MB each, 1:1

A YouTube image post takes JPG, PNG, GIF or WEBP files up to 16 MB, with up to 10 images per post. YouTube suggests 1:1 because that is how the feed shows them, and it suggests music of up to 15 seconds that plays when the post appears in the Shorts feed. These are the numbers on YouTube Help, read 2026-10-01.

What are the image post limits?

How do I generate 1:1 images for a post?

POST /v1/images takes aspect_ratio: "1:1" and an output_format of png, jpeg or webp, all three inside YouTube's list. n takes 1 to 4 images per request, so a 10-image post is three requests. Catalog models accept only the values their descriptors list, so check supported_parameters first.

curl -X POST https://api.sume.com/v1/images \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "sume/auto",
    "prompt": "A clean product shot on a plain background",
    "aspect_ratio": "1:1",
    "output_format": "jpeg"
  }'

Can Sume output GIF?

No. The Image API's output_format is png, jpeg or webp in the catalog descriptors (the docs also mention svg), and GIF is not on either list. Use JPG, PNG or WEBP for these posts.

How do I keep each file under 16 MB?

Sume's image docs do not document a file-size field or a compression setting (output_compression is listed as not served in v1). Check each delivered file's size yourself, and pick jpeg or webp over png if a file runs large.

What about a video instead?

Image posts are a separate path from Shorts video. For a vertical clip, Timeline 1.0 defaults to 1080x1920 MP4. See the related Shorts video specs post.