Next-episode end card in Timeline 1.0: held still, fade, cliffhanger

How do you add a 'next episode' end card to an AI micro-drama? Put a still image in the last Timeline 1.0 video slot, hold it for a second or two with a fade transition, and render. Stills are static holds, a transition is capped at 1 second, and the render costs $0.10 per ceil output minute.

Serialized vertical drama lives on the last frame: each episode ends on a cliffhanger, and YouTube's new Shorts series feed puts the next episode one swipe away. A held card gives the viewer a beat to tap.

The request

Timeline 1.0 takes one audio spine plus ordered video slots. Every URL must be a media.sume.com artifact or asset of your workspace; import files first. Idempotency-Key is required. The last slot below is a still, held for 2 seconds after a 0.5 second fade.

{
  "audio": { "url": "https://media.sume.com/artifacts/artf_demo/ep3-voice.wav", "duration_seconds": 45 },
  "video": [
    { "source_url": "https://media.sume.com/artifacts/artf_demo/ep3.mp4", "start": 0, "duration": 43 },
    { "source_url": "https://media.sume.com/artifacts/artf_demo/next-card.png", "start": 43, "duration": 2,
      "transition": { "type": "fade", "duration": 0.5 } }
  ]
}

Rules that matter here

video[0].start must be 0, later starts must increase, and each slot's duration must be at least 0.2 seconds. Coverage can stop at most 0.5 seconds before the end of the spine, so make the card's end match the voice track length. A transition is limited to 1 second and 50% of the shorter neighbor, and it cannot sit on the first slot (transition_on_first_segment).

If you give the still a motion field, the job accepts it and ignores it, reporting motion_ignored; that is a soft warning, not a failure.

Check before paying

POST /v1/timeline-1.0/plan is an unbilled compile preflight. It returns duration_seconds, segment_count, billable_minutes and an estimated cost, and it does not create a job. Run it in CI for every episode and you catch a bad start time before a render slot is spent.

Shorts series episodes are portrait or square and up to 180 seconds, so a 45-second episode with a 2-second card fits with room to spare.

Reusing the card

The end card is a template. Keep the still, the fade and the duration in one timeline fragment, then swap only the episode number and the next-release text each week. Because the plan endpoint is free, you can test each variant without paying. The only billed step is the final render.