compose_image_not_still and compose_video_not_video: the fix
Sume Timeline compose probes both URLs: image.url must be a still, video.url a video. Failing either refuses the request; off-host URLs need an import first.
Sume's compose probes both inputs. image.url must probe as a still, or the request fails with compose_image_not_still; video.url must probe as a video, or it fails with compose_video_not_video. Both must already be on this workspace's media.sume.com.
This is from the Timeline compose docs, read 2026-10-01. If you came from Runway's Premiere Pro panel news, note that the API takes hosted URLs, not timeline selections.
What triggers each refusal?
The two checks are mirror images, so the usual cause is swapped fields.
| Code | Meaning | Common cause |
|---|---|---|
compose_image_not_still | image.url is not a still | A video URL in image |
compose_video_not_video | video.url is not a video | A PNG or JPEG in video |
What about off-host URLs?
Off-host URLs such as https://example.com/... are rejected at admit. A dead or off-host URL surfaces as source_not_found or unsupported_media_source; the docs list the two codes together.
How do I import a file first?
Call POST /v1/media-imports to bring the file onto media.sume.com, then use the returned URL in the compose body.
Can I animate the still instead?
Compose holds the still for the whole clip. If the image is really a short video, pass it as video and use a still for image. The same stack and overlay layouts then apply; see stack an image over a video.
Sources
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