How it works
Timeline and playback
One clock runs the whole scene. The preview reads it, the thumbnails read it, and the encoder reads it — which is why the file you export is frame-for-frame the clip you watched.
Frames, not seconds
The scene is a whole number of frames: the duration in seconds times the frame rate. Everything downstream is asked for a frame index, never for a timestamp, so there is no rounding drift between what plays and what encodes.
Changing the frame rate keeps the moment you were looking at rather than the frame number, so the playhead does not jump to a different part of the clip when you go from 30 to 60.
The ruler and the playhead
The ruler is labelled every two seconds with three ticks between, so a beat lands on something you can see. Drag the playhead to scrub; the scene recomputes at that frame rather than replaying up to it, so scrubbing backwards costs the same as scrubbing forwards.
Duration is part of the motion
It is tempting to treat clip length as packaging, and for most families it is. For the ported ones it is not: their cadence was authored in seconds per card, so the duration is what pins how fast a card advances. Those presets set the length when you pick them, and changing it afterwards genuinely changes the motion — a settle becomes a drift.
This is also what makes loops clean. Speeds are quantised to a whole number of motion cycles per clip, so the last frame lands exactly where the first one starts. See Easing for why a curve cannot break that.
Lanes are tracks
Each lane below the ruler is a motion track with its own template, values and window. The gutter beside a lane carries its visibility, its stacking, and the duplicate and remove actions — and the selected lane is the one the control panel is editing, which is the single most useful thing to keep an eye on when a slider seems to do nothing.
A lane also carries a blend mode. The renderer draws one container per track, in order, so a lane set to something other than normal composites against the lanes beneath it rather than simply covering them — which is how a light wash or a texture pass goes over a carousel without hiding it.
Tracks never keep their own clock. Each is handed the length of its own window, so it loops inside that window, and a single track spanning the whole clip behaves exactly like having no tracks at all. Motion tracks goes into it.
Undo covers gestures
A whole drag is one step back, not forty. So is a typed number and a template pick. The history coalesces by gesture on purpose: undoing a slider drag one pixel at a time is not undo, it is punishment.