Add a launch date plate to a teaser video with compose overlay

To put a launch date on a teaser, design the date as a still plate, then call Timeline compose with operation: "overlay", your plate as image.url and the teaser as video.url. You get one MP4 back for $0.02 flat, and you can drop it into a Timeline 1.0 render afterwards.

What does the overlay operation do?

Compose takes exactly one still and one video and puts both on screen at once. stack tiles two regions; overlay sits the still over the video. The HTTP field is operation, not mode; mode stays the usual async or sync option.

Output length always comes from the video layer, either video.duration or the rest of the file from source_in. The still is held for the whole clip and can never lengthen it. The ceiling is 300 seconds, which is generous for a teaser.

Which layout keys apply to an overlay?

Mixing stack keys (split, image_region, ratio) with overlay keys is a 400, as compose_stack_takes_no_overlay_layout or compose_overlay_takes_no_stack_layout.

What does the request look like?

Both URLs must already be this workspace's media.sume.com media, so import the plate and the teaser first. Idempotency-Key is required.

curl -X POST https://api.sume.com/v1/timeline-1.0/compose \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: launch-plate-001" \
  -d '{
    "operation": "overlay",
    "image": { "url": "https://media.sume.com/artifacts/artf_demo/oct-14-plate.png" },
    "video": { "url": "https://media.sume.com/artifacts/artf_demo/teaser.mp4" },
    "layout": { "position": "bottom", "width_ratio": 0.8, "margin_ratio": 0.06 },
    "output": { "width": 1080, "height": 1920 }
  }'

What will the output look like?

Default output is 1080 by 1920 at the video layer's own frame rate, the only rate that repeats or drops no frame. Set output.width and output.height to the timeline you will assemble into, so the shot is not rescaled twice. An explicit output.fps different from the clip's rate warns output_fps_resamples_sources.

Audio passes through from the video. A mute teaser is a warning (compose_video_has_no_audio), not a failure; the Timeline 1.0 spine supplies sound when you assemble. A video.duration past the file clamps with compose_duration_clamped_to_source. Both are soft warnings and the job still succeeds.

How do you make the plate?

Make it in any design tool, or generate it with Sume's image tools, and export an image at the aspect you want. Compose requires the plate to probe as a still (compose_image_not_still otherwise). The docs do not describe how transparency is handled, so design the plate as a complete card with its own background, and look at the render before publishing.

How does this fit into a teaser sequence?

Compose builds one shot. For a sequence, produce each shot with its own plate (for example one per launch phase), then place the shots in a Timeline 1.0 render, where adjacent video[] slots follow each other and transition types like fade or dissolve join them. Use the same output size on compose and on the render so nothing is rescaled twice.

Check the result at a phone's size, and leave enough margin_ratio that the plate is not hard against the frame edge.

What is a safe workflow for date variants?

Export the plates as separate files named by date, import them once, and loop over them with a unique idempotency key per plate. Each compose is a $0.02 job, so ten date variants cost $0.20 at the published rate. Spot-check the first and last render, and keep the original teaser untouched: compose returns a new artifact each time.

What does this not do?

Compose is one still plus one video. It does not animate the plate, count down, or place several plates; for a countdown, build a shot per day and sequence them in Timeline 1.0. A changed date means a new plate and a new $0.02 compose job, so batch your date variants.