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Loop Fixer

Eliminate the "pop" at the loop seam. Two modes, live preview, no manual keyframes required.

Tier: Builder Pro Menu: Polish → Loop Fixer Shortcut: Ctrl + Shift + L

What it does​

Looping animations cycle from frame N (the last frame) back to frame 0 (the first frame) instantly. If the pose at frame N differs from the pose at frame 0, the playback shows a visible discontinuity — the dreaded "pop" — every time the loop wraps. Loop Fixer pulls the tail of the animation toward frame 0's pose so the cycle reads as seamless.

Two correction strategies:

  • Snap mode: replace (or insert) a keyframe at exactly t = duration with frame 0's value. Hard cut, perfect mathematical loop, may show a one-frame jump just before the seam if the original tail diverged sharply.
  • Blend mode: smoothstep ramp the last N keyframes toward frame 0's value. The closer to the seam, the more the bone is pulled toward frame 0. Soft, gradual, no visible jump.

Both modes operate on clipData tracks — the result survives playback, retarget, and export.

Kinetiq Engine Loop Fixer modal — mode toggle between Snap and Blend, blend duration slider, live preview viewport showing the closing keyframes settling toward frame 0, A/B compare Press & Hold for Source button, and Apply / Cancel actions

The Loop Fixer modal. Pick Snap for a hard mathematical loop or Blend for a smoothstep ramp; drag the blend duration slider and watch the seam tighten in real time. Press and hold the amber A/B button to A/B against the original “pop” before you commit.

Snap vs. Blend — when to use which​

Use Snap when:​

  • The clip is short (under 1 second) and a one-frame jump won't be perceptible.
  • You're testing the concept of a loop and need a quick perfect closure to validate.
  • Frame N's pose is already very close to frame 0's pose (a hard cut just refines what's almost there).

Use Blend when:​

  • The clip is longer than ~1 second.
  • Frame N and frame 0 are visibly different (e.g., walk cycle that wasn't authored as a loop).
  • You want the loop to read as natural rather than mathematically perfect.

In practice, Blend is the right answer for ~95% of clips. Snap exists for the edge cases.

Blend duration scrubbing​

When in Blend mode, the Blend Duration slider controls how many tail frames participate in the ramp.

Blend Duration: 10 frames
[●━━━━━━━━━━━━━━━━━━]
1 (Sharp)              30 (Soft)
  • Sharp (1-3 frames): the ramp finishes quickly. Most of the original tail survives, only the last few frames blend. Useful for fast / punchy animations where a long blend would visibly slow the motion.
  • Soft (15-30 frames): the ramp is gentle and gradual. The last half-second-ish of the clip blends. Useful for slow / cinematic motion where any abrupt change is jarring.

The slider's max range is the clip's total frame count, so a 60-frame clip lets you blend up to 60 frames (i.e., the entire clip). A 20-frame clip caps at 20.

The viewport updates live as you drag — no preview button, no commit. Find the visual sweet spot, then click Apply.

Sample on demand — no keyframes required​

The previous Loop Fixer (v1) hard-required explicit keyframes at frame 0 and frame N - 1 to function. After any retarget operation, those keyframes were silently dropped, and the feature became unusable until the user manually re-authored them. This was the wall many users hit when they tried "Select All" looking for a way out.

V2 removes that requirement. The fix operates on TrzClipData tracks directly — and clipData tracks are continuous (the mixer interpolates between keyframes for any time). So Loop Fixer can:

  • Read frame 0's value by sampling the first keyframe of each track (no explicit keyframe at t = 0 needed; the mixer extrapolates the first value backward).
  • Write the closure value at exactly t = duration by appending a new keyframe if none exists, or replacing the existing one.

The amber warning "Requires keyframes at frame 0 and frame N" that defined v1 is gone. Just open the modal and apply.

Live preview + A/B Compare​

The modal carries the same live-preview pattern as Mirror Animation:

  • Snapshot on open: when you launch the modal, the current clipData is deep-cloned into memory.
  • Live re-mirror on every control change: switch modes, drag the slider, toggle Frame range — the viewport repaints with the corrected loop, RAF-debounced for smoothness.
  • Apply commits: click Apply Mirror and the latest preview is promoted to the canonical clipData.
  • Cancel restores: Cancel or X re-installs the snapshot. The viewport returns to the exact state it had before you opened the modal.
  • A/B Compare (amber button): Press & Hold to peek at the original (with the pop). Release to see the fixed version. Verify the improvement is real before committing.

Workflow — typical session​

  1. Play your animation with Loop enabled in the timeline. Watch for the seam.
  2. Spot a visible pop at the wrap point.
  3. Polish → Loop Fixer (or Ctrl + Shift + L).
  4. Modal opens. Default mode is Blend, default duration is 10 frames.
  5. Watch the viewport — the seam should be visibly smoother already.
  6. (Optional) Drag the slider toward Soft until the loop reads as completely seamless.
  7. Hold the A/B button briefly to confirm the improvement.
  8. Apply to commit.
  9. Re-watch playback. The pop should be gone.

Math — smoothstep blending​

For each existing keyframe whose time t falls inside the blend window [duration - blendFrames/fps, duration]:

alpha = (t - blendStart) / blendDuration       // 0..1, normalized progress through the window
sa    = alpha² × (3 - 2·alpha)                 // smoothstep easing — zero derivatives at endpoints

The keyframe's value is then blended toward frame 0's value:

output_quaternion = slerp(original, frame0, sa)
output_position   = lerp(original,  frame0, sa)
output_scale      = lerp(original,  frame0, sa)

At the start of the window (alpha = 0), the keyframe is untouched. At the end (alpha = 1), the keyframe is exactly frame 0's value. In between, smoothstep gives the eased curve that has zero velocity at both endpoints — the mathematically smoothest one-frame interpolation.

Plus, after the loop, Loop Fixer always pins a keyframe at exactly t = duration with frame 0's value. This guarantees the loop closure is mathematically tight regardless of where the last existing keyframe lands.

In Snap mode, the math is trivial: skip the smoothstep loop entirely, just write/replace the keyframe at t = duration with frame 0's value.

Edge cases​

Clips with only one keyframe​

If a track has only a keyframe at t = 0 (a static pose), Snap and Blend behave identically: append a keyframe at t = duration with the same value. Result looks like a static pose for the full duration. No-op visually, but the loop is mathematically valid.

Clips with no keyframe at t = 0​

Loop Fixer reads the first keyframe's value as "frame 0's value" regardless of its time. So if the first keyframe is at t = 0.5, Loop Fixer treats that as the loop target. This matches what the mixer does (it extrapolates the first value backward for t < first_time).

Frame 0 already equals frame N​

The fix is a no-op visually, but Loop Fixer still pins the closure keyframe at t = duration — making the math airtight even if there's no observable change.

Mirror + Loop Fixer in the same session​

Apply Mirror first, then Loop Fixer. Mirror modifies the per-frame poses; Loop Fixer ensures the modified end matches the modified start. Done in the other order, you'd close a loop on the original animation and then mirror the closed loop — typically not what you want.

  • Mirror Animation — the other Polish-menu tool, also clipData-based with live preview
  • Quality Score — measures loop continuity as one of its sub-metrics
  • What's New — Kinetiq 1.0 launch overview