Synthesia accepts WebP with transparency: what Sume avatar URLs need

Synthesia's updates page lists WebP support on September 29, 2026, for animated or static images, with transparency preserved. That is a statement about Synthesia's editor. For Sume Avatar 1.0, the rule is about the URL, not the format name: avatar photo and product image inputs must be public HTTPS URLs whose content type matches the file, or the request is rejected before submission.

What Synthesia says

The entry is short: WebP images work in either animated or static form and transparency is kept. It does not describe limits, so read the live page before relying on it for a specific file.

What Sume checks

The media input rules reject localhost, private-network, signed and private URLs, and any URL whose content type does not match the file. The docs do not promise acceptance of every image format, so I would not assume WebP will pass; test with a small file first and fall back to JPEG or PNG.

For avatar creation the photo goes in input.photo.image_url. For videos, product_image and a photo scene are the optional image inputs.

curl -X POST https://api.sume.com/v1/avatar-1.0/generate \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"avatar_handle":"host_test","input":{"photo":{"image_url":"https://example.com/host.png"}}}'

A safe routine

Convert to PNG or JPEG if your tool exports WebP, serve it from a stable public host, and confirm the server sends the matching Content-Type header. Then preview the first frame before you render long.

Transparency is a design choice for a scene, not an avatar input; use a scene photo or prompt for backgrounds.