Does a crossfade shorten a Short? Timeline start times explained

No. A crossfade in Sume Timeline 1.0 does not shorten the video. Each slot's start is authoritative, and the compiler compensates for the overlap instead of moving later slots earlier. The output length is the declared audio.duration_seconds. Read from the Timeline docs on 2026-10-06.

Why do other editors lose time to a crossfade?

Many timeline tools overlap two clips by the transition length, so a ten-clip montage with half-second fades ends up several seconds shorter than the sum of its clips. When a platform limit is tight, that drift matters. Sume's rule removes it: you declare where each slot starts on the audio spine and the render follows.

What does the compiler do instead?

The docs say the compiler compensates for xfade and never pre-shifts a start. In practice, write starts as the cumulative sum of the slot durations you want on screen, and the overlap is absorbed inside the transition. The final video is cut to the declared length with -t.

{
  "audio": {"mode": "silence", "duration_seconds": 12},
  "video": [
    {"source_url": "https://media.sume.com/artifacts/artf_demo/a.mp4", "start": 0, "duration": 6},
    {"source_url": "https://media.sume.com/artifacts/artf_demo/b.mp4", "start": 6, "duration": 6,
     "transition": {"type": "fade", "duration": 0.5}}
  ]
}

How do I confirm the length?

Send the same document to POST /v1/timeline-1.0/plan first. It is unbilled and returns duration_seconds, segment_count and billable_minutes, so you can confirm 12 seconds and one billable minute before rendering.