FFmpeg xfade has 59 transitions: which does Sume Timeline take?

FFmpeg's xfade filter page lists 59 values for transition, custom included. Sume's Timeline 1.0 accepts six on a video[] slot: fade, wipeleft, wiperight, slideup, slidedown and dissolve. All six are names FFmpeg also lists, so a six-type look ports; the other 53 do not exist on Sume, and a circleopen or zoomin has no Timeline field.

FFmpeg facts are from the Filters Documentation, read 2026-10-02. Sume facts are from the Timeline 1.0 docs.

What does FFmpeg require for xfade?

The page says both inputs must be constant frame-rate and have the same resolution, pixel format, frame rate and timebase. duration ranges from 0 to 60 seconds (default 1) and offset sets the start relative to the first input (default 0). A custom transition takes an expr expression. In a raw FFmpeg command you compute each offset yourself.

How does Sume's Timeline handle the same job?

You declare each slot's on-spine start and duration and an optional transition on slots after the first. The docs say declared starts are authoritative and the compiler compensates for the crossfade; you never pre-shift. Transition duration must be at most 1 second, at most 50% of the shorter neighbouring slot, and at least one output frame. More than 8 adjacent fades is refused as too_many_chained_transitions; insert a hard cut. A transition on video[0] is transition_on_first_segment.

Resolution and rate are set once: output.width / output.height (even integers 256 to 2160) and output.fps (24, 25, 30 or 60), with fit per slot (cover, contain, stretch, blur). Mixed-size sources do not need matching first.

{
  "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": "wipeleft", "duration": 0.5 } }
  ]
}

Which names overlap?

Send the body to POST /v1/timeline-1.0/render with an Idempotency-Key; POST /v1/timeline-1.0/plan is the unbilled preflight.