Runway Compositing Nodes vs Sume Timeline compose

Runway's changelog says compositing workflow nodes let you compose and blend images and video together, available to all customers. Sume's nearest feature is narrower: Timeline compose takes one still and one video, both already hosted on Sume, and returns one MP4 with both on screen, either stacked in one frame or as an overlay.

Runway's entry is one sentence, so this post compares only what it states. Sume facts are from Timeline compose, read 2026-10-01.

What does Timeline compose accept?

Required fields are operation (stack or overlay), image.url and video.url, plus an Idempotency-Key. The HTTP field is operation, not mode; mode is the usual async or sync communication option. The route is POST /v1/timeline-1.0/compose, and you poll the job at GET /v1/jobs/:id/status.

How long is the output?

Output length always comes from the video layer. The still is held for the whole clip and can never lengthen it, with a ceiling of 300 seconds. Audio passes through from the video; a mute video is a warning, not a failure.

What are the limits?

Both URLs must already be this workspace's media.sume.com artifact or asset, so import outside media first with POST /v1/media-imports. Off-host URLs are rejected at admit. Sume compose is one shot: sequencing, transitions and the audio spine stay on Timeline 1.0. If you need blend filters between two clips instead, see blend two videos together.

What does a compose job cost?

The docs list a flat $0.02 per job and say to confirm it live in GET /v1/catalog. It is flat because video.duration may be omitted until the worker probes the file.