Reframe

A reframe track lists subject centers keyed by sourceMs, the asset media time, with x and y from 0 to 1 across the source frame. On a video the track sits beside a crop, and the renderer slides the crop window onto each center. A video without a crop ignores its track. On a multicam the track sits on one source, and every layout slot that shows that source slides its window the same way, so each slot keeps its rect. A slot with a crop slides the crop, and a slot without one slides the part of the frame its fit shows. The window stops at the frame edge. When a slot's crop stops there, the fitted part inside the crop keeps moving toward the subject until it meets the crop's edge. Keys follow the media, so trims, splits, slips, and speed changes keep them aligned. A zoom region on the same clip or slot starts from the reframed window and narrows from there.

engine.dispatch({
  type: 'setReframe',
  elementId: 'e-multicam',
  source: 'camera',
  track: [
    { sourceMs: 0, x: 0.42, y: 0.4 },
    { sourceMs: 4000, x: 0.58, y: 0.4 },
  ],
})

A null track removes tracking and keeps the crop. Writing the same track again is a no-op with no undo step. planCenterPerson from @mcut/editor builds this command from face samples.

Functions

getReframeCenter

getReframeCenter(element, sourceKey, timelineMs) returns the subject center { x, y } of a video, or of the multicam source named by sourceKey, at one timeline instant, or null when there is no track. It maps the instant to source media time, interpolates linearly between keys, and holds the first and last key outside them.

centeredFocus

centeredFocus(center, visible) returns the focus anchor that puts center in the middle of a window that shows visible, the { x, y } fraction of the frame on each axis, with center in the same 0 to 1 coordinates. For a slot with a crop both are measured across the crop. It is the same VisibleFraction that getSlotView takes, and the anchor is the rest focus getSlotView takes. The anchor clamps so the window stays inside the frame, and an axis where the window spans the whole frame anchors at 0.5.