Compose stacks a still over a video for up to 300 seconds, flat $0.02
A 3-minute Short with a headline image on top fits Sume timeline compose's 300-second ceiling at a flat $0.02. How the stack is sized and what clamps.
Yes, a stacked 3-minute Short fits: Sume's timeline compose takes a clip of up to 300 seconds and charges a flat $0.02 per job. A still on top of a video, or an overlay plate, over a 180-second clip is one compose call, well inside the ceiling.
The numbers are in the timeline compose docs (read 2026-10-06): the ceiling is 300 seconds, the rate is flat at $0.02 because the duration may not be known before the worker probes the video, and the default output is 1080x1920 MP4. YouTube's three-minute Short limit is 180 seconds.
How does the stack decide its length?
The output length always comes from the video layer: video.duration, or the rest of the file from video.source_in. The still stays on screen for the whole clip and can never make it longer. If you ask for more than the file has, the job clamps and returns the warning compose_duration_clamped_to_source; it still succeeds.
What layout keys are there?
Mixing stack keys with overlay keys returns a 400 (compose_stack_takes_no_overlay_layout).
| Key | stack | overlay |
|---|---|---|
split | horizontal or vertical | Not permitted |
ratio | Still's share of the frame, 0.1 to 0.9 | Not permitted |
width_ratio | Not permitted | 0.05 to 1 of width, default 0.9 |
margin_ratio | Not permitted | 0 to 0.45 of height, default 0.05 |
What do I do with a source longer than 300 seconds?
Not an issue for a Short, but for a longer reel cut it first with video trim into pieces of 300 seconds or less, compose each, and join them in Timeline 1.0. Set output.width and output.height on compose to match the Timeline you assemble into so the clip is not rescaled twice.
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