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Sequencer Keyframe Interpolation

The supported interpolation modes are:

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This document records the TODOS.phase-72.72.15.1.3 cinematic sequencer keyframe interpolation contract. Interpolation is authored as named specs that can be referenced by a keyframe's InterpolationId and constrained by track PropertyPath, giving the sequencer both per-keyframe and per-property interpolation behavior.

Runtime Ownership#

  • Runtime module: V2Cinematics
  • Interpolation spec: FV2SequencerInterpolationSpec
  • Interpolated value: FV2SequencerInterpolatedValue
  • Interpolation issue: FV2SequencerInterpolationIssue
  • Mode enum: EV2SequencerInterpolationMode
  • Issue enum: EV2SequencerInterpolationIssueType
  • Automation: V2.Cinematics.Sequencer.KeyframeInterpolation
  • CI checker: V2/ue/Tools/check-v2-sequencer-keyframe-interpolation.py

Modes#

The supported interpolation modes are:

  • Step, which holds the previous keyframe value.
  • Linear, which blends float, vector, and rotator values by normalized alpha.
  • CubicBezier, which uses normalized 0-1 control points for cinematic easing.
  • CustomCurve, which records a CustomCurveId and evaluates a deterministic runtime ease curve until authored curve assets are available.

Discrete bool, name, and string tracks use step fallback even when a non-step spec is selected, preserving deterministic event and state behavior.

Per-Property And Per-Keyframe Resolution#

BuildDefaultSequencerInterpolationSpecs seeds:

  • Interpolation.Linear for Transform.Location.
  • Interpolation.CubicEaseInOut for CineCamera.FieldOfView.
  • Interpolation.Step for GameplayEvent.
  • Interpolation.Custom.CameraEase for CineCamera.FieldOfView with Curve.Cinematic.CameraEase.Custom.

ResolveSequencerInterpolationSpecForKeyframe first matches a keyframe's InterpolationId, then falls back to a matching PropertyPath, then creates a linear default for the track. This keeps old keyframes readable while allowing new per-property overrides.

Evaluation#

EvaluateSequencerKeyframeInterpolation finds the previous and next keyframes around the requested frame, resolves the interpolation spec, computes normalized alpha, applies the selected interpolation mode, and returns a FV2SequencerInterpolatedValue containing the typed result plus source/target keyframe ids. Empty tracks, untyped values, and mismatched source/target value types report issues through FV2SequencerInterpolatedValue::Issues.

Verification#

Run:

bash
python3 V2/ue/Tools/check-v2-sequencer-keyframe-interpolation.py

Adjacent verification should include python3 V2/ue/Tools/check-v2-sequencer-data-model.py, python3 V2/ue/Tools/check-v2-sequencer-timeline-playback.py, and python3 V2/ue/Tools/check-v2-cinematics-module.py.