Circle Iris — effect skill for transitions

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B opens from (or A closes into) a growing circle, like an old-cartoon iris or a lens opening.

What it does

Built on SDF Iris by HeyGen (HyperFrames), Apache-2.0. The write-up and recipes below are varg's.

A circular window expands from the subject or the centre until B fills the frame.

When: Spotlighting a subject, playful and retro edits, focus on a product.

Watch out: Off-centre irises that cut through faces; centre the circle on the subject.

Timing: 0.5–0.8 s, ease-in-out (hold 2–6 frames as a dot for the cartoon iris)

Also called: circle mask, iris wipe, iris in, iris out, circle open, Circular Slices II

In FFmpeg

Same size/fps/pixel format on both inputs (see the Normalize card). offset = duration(A) - T = 5.0 - 0.6 = 4.4.

ffmpeg -i a.mp4 -i b.mp4 -filter_complex \
"[0:v]fps=30,settb=AVTB,format=yuv420p[a];[1:v]fps=30,settb=AVTB,format=yuv420p[b];\
[a][b]xfade=transition=circleopen:duration=0.6:offset=4.4[v];\
[0:a][1:a]acrossfade=d=0.6[au]" \
  -map "[v]" -map "[au]" -c:v libx264 -crf 18 -c:a aac out.mp4

circleclose shrinks a circle; circlecrop irises out to black and back in. Off-centre: transition=custom:expr='if(lt(hypot(X-800,Y-400),(1-P)*1600),B,A)' (P runs 1→0 during xfade).

In HyperFrames

Shader sdf-iris from @hyperframes/shader-transitions placed at the cut (t = 4 s):

<div id="s1" class="scene" style="background:#0a0a0a"><video src="a.mp4" muted playsinline></video></div>
<div id="s2" class="scene" style="background:#0a0a0a"><video src="b.mp4" muted playsinline></video></div>
<script src="https://cdn.jsdelivr.net/npm/@hyperframes/shader-transitions/dist/index.global.js"></script>
<script>
  const tl = HyperShader.init({ bgColor: "#0a0a0a", scenes: ["s1", "s2"],
    transitions: [{ time: 4, shader: "sdf-iris", duration: 0.7 }] });
  window.__timelines = window.__timelines || {}; window.__timelines["main"] = tl;
</script>

Each .scene needs an explicit background-color equal to bgColor. Or install the ready block: npx hyperframes add sdf-iris. CSS: npx hyperframes add iris-reveal (clip-path circle from an authored origin).

In Remotion

import {TransitionSeries, linearTiming, springTiming} from '@remotion/transitions';
import {iris} from '@remotion/transitions/iris';

<TransitionSeries>
  <TransitionSeries.Sequence durationInFrames={90}><ShotA /></TransitionSeries.Sequence>
  <TransitionSeries.Transition presentation={iris({width: 1920, height: 1080})} timing={linearTiming({durationInFrames: 20})} />
  <TransitionSeries.Sequence durationInFrames={90}><ShotB /></TransitionSeries.Sequence>
</TransitionSeries>

Total = 90 + 90 - 20 frames: the transition overlaps the two shots. iris() requires width and height (the composition size).

In CapCut

Transitions tab → Mask → circle-shaped mask transitions (e.g. Circular Slices II). Desktop: drag the tile onto the cut between two clips and set Duration in the right panel ("Apply to all" reuses it on every cut). Mobile: tap the small white square between clips, pick the transition, drag the duration slider, tap ✓. Tab labels and placement change between versions and regions. Hand-made: add a Mask → Circle on B and keyframe its size from 0 to full.

Ready-made components

Where this comes from

Use when

Not for

Install

Example output

https://s3.varg.ai/how-to/previews/07c5ad2e6741/take-circle-iris.mp4 — circleopen between two shots, with the timeline strip of the edit. Footage: Spring (2019), Andy Goralczyk / Blender Foundation (Blender Studio) | studio.blender.org, CC BY 4.0; Big Buck Bunny (2008), (c) copyright 2008, Blender Foundation | www.bigbuckbunny.org, CC BY 3.0. (credit: Rendered by varg · Spring (2019) + Big Buck Bunny (2008))

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