Slide-up transitions for a vertical Short: Sume Timeline types, limits

Sume Timeline 1.0 offers six transitions: fade, wipeleft, wiperight, slideup, slidedown, and dissolve. For a vertical Short, slideup is the one that mimics a feed swipe. Each transition is at most 1 second, at most 50 percent of the shorter neighboring slot, and at least one output frame long.

These are the rules in the Timeline 1.0 docs (read 2026-10-06). A transition is only allowed on slots after the first; on the first slot the request is refused with transition_on_first_segment.

Which type for which feel?

The figures are laid out below.

How do I add one?

On a slot after the first, add "transition": {"type": "slideup", "duration": 0.3}. The declared start values stay authoritative: the compiler compensates for the overlap and never pre-shifts your slots. The job renders durations snapped to the frame, so 0.3 seconds at 25 or 30 fps may come out a hair different, and a duration that cannot align can return transition_not_frame_aligned.

What are the limits of using many of them?

More than 8 adjacent transitions are refused (too_many_chained_transitions); put a hard cut every so often. A transition that is too long for a neighbor is refused (transition_too_long), or, for a clip too short to hold one, you may get a warning rather than a failure. Run POST /v1/timeline-1.0/plan to see errors before you submit.