Sale intro card, then the clip: two timeline slots, not compose

If you want a sale card on screen first and the product clip after it, use two adjacent video[] slots in a Sume timeline-1.0 render: the still in slot 0 and the clip in slot 1. Compose is for the other case, where one still and one video are on screen at the same time. The compose docs say it directly: sequential image-then-video is not a compose mode.

The slot rules are in Timeline 1.0 and the compose scope in Timeline compose, both read 2026-10-06. A still in a timeline slot is a static hold, with no motion.

How do the two slots look?

The card holds for the first two seconds, then a short fade leads into the clip. Slot 0 must start at 0, the second slot must start later, and only the second slot may carry a transition. The audio spine sets the total length, so audio.duration_seconds must cover both slots.

curl -X POST https://api.sume.com/v1/timeline-1.0/render \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: sale-card-then-clip-001" \
  -d '{
    "audio": { "mode": "silence", "duration_seconds": 8 },
    "video": [
      { "source_url": "https://media.sume.com/artifacts/artf_demo/sale-card.png",
        "start": 0, "duration": 2 },
      { "source_url": "https://media.sume.com/artifacts/artf_demo/product.mp4",
        "start": 2, "duration": 6,
        "transition": { "type": "fade", "duration": 0.25 } }
    ]
  }'

When is compose the right tool?

Use compose when the card and the clip share the frame for the whole shot: a price plate over the footage, or a half-banner with the still on top. Then drop the composed MP4 into a timeline slot.

What does it cost?

The render above bills one output minute at $0.10, since 8 seconds rounds up. A compose job is $0.02 flat. The docs point to GET /v1/catalog for the live rate.

• audio.mode: "silence" declares a length with no spine file, and takes no url, parts, gain_db, or source_in.
• If your clip has sound you need, give the timeline a real spine instead of silence.
• Stills ignore source_in, so trim the clip, not the card.