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Content & Media Creation · iart-ai/motion-design-skills

beat-sync-editing

This skill should be used when the user asks to "cut to the beat", "fix the pacing", "edit this sequence", "sync cuts to music/BPM", "add a match cut / J-cut / L-cut", "build a speed ramp", or "plan a shot sequence / edit timeline". Covers editing rhythm, transitions, retiming, and translating an edit plan to an NLE or a code timeline (Remotion/AE frames).

L1 Basic · Source registration onlyV1 Commit-PinnedDual-pass Audit
Author iart-aiGitHub iart-ai/motion-design-skills ↗Stars 28License MIT（仓库根 LICENSE：Copyright (c) 2026 iart.ai；.claude-plugin marketplace.json/plugin.json 同声明）Commit 3c129f769d
Control levels describe skill capabilities and suggested control measures; they do not represent quality or safety certifications, nor do they dictate usability. Usage decisions rest entirely with users and administrators. Different agent hosts apply varying constraints; do not assume hosts provide automatic protection. Third-party skill copyrights belong to their original authors. Use at your own risk.

1How It Works & Mechanism

Pure methodology/computation skill: zero scripts, zero network access; the core concept is converting musical rhythm into frame-accurate editing mathematics—frames_per_beat = (60/BPM) × fps—emphasizing cuts on musical phrases (2/4/8 beats) rather than on every single beat.

skills/beat-sync-editing/SKILL.md
frames_per_beat = (60 / BPM) * fps
The formula appears in '### 1. Find the grid: BPM → frames'; at 120 BPM/30fps = 15 frames/beat. All cut points, J/L offsets, and speed ramp targets expand from this conversion, serving as the foundational root of 'why it snaps to the beat'.

Translates 'editing intuition' into decision trees and reference tables: the decision tree diagnoses by symptom (off-beat, jarring cuts, sluggish pacing, weak impact, handoff to code), routing each symptom to a specific family of techniques.

skills/beat-sync-editing/SKILL.md
What's the editing problem?
The root features 5 branches corresponding to 5 core workflow sections (grid, cut-on-action, transitions, retime, arc), each terminating in concrete frame numbers—highly structured so an agent can follow it step-by-step.

Transitions are governed by motivated discipline: default to hard cuts (accounting for 90%), using match/J/L/whip cuts only when clearly justified, with each transition type accompanied by an 'align what / signals what / typical offset frames' table.

skills/beat-sync-editing/SKILL.md
Default to the **hard cut**. Reach for anything else only when motivated:
J-cut = incoming audio leads visual by 4–12f; L-cut = outgoing audio trails by 12–24f. Offsets are explicitly expressed in frame counts, ensuring practical implementation in both NLEs and code timelines.

Provides frame-by-frame recipes for speed ramps: run-up → ease down to 25% → IMPACT lands on beat → release, requiring optical-flow/frame-blending and consistent shutter settings to prevent strobing.

skills/beat-sync-editing/SKILL.md
Speed ramps (gradual time-warp) add impact: ramp *into* a hit with slow-motion, then snap back to speed.
Both SKILL.md and reference provide frame-by-frame tables (30fps examples); with concrete implementations provided for both targets: AE (time remap + Pixel Motion) and Remotion (eased interpolate).

The overall pacing arc is modeled as Establish → Develop → Climax → Resolve, where tension is the derivative of cut frequency: gradually shorten the average shot length toward the climax, followed by a long hold after the peak.

skills/beat-sync-editing/SKILL.md
Establish → Develop → Climax → Resolve
SKILL.md includes the quantitative formulation 'energy is the *derivative* of cut frequency' alongside a 4-phase table (cutting every 8–16 beats → 1–2 beats → long hold), turning 'dynamic pacing' into computable parameters.

Produces a renderer-agnostic edit-timing plan (track spec, arc, cut list, transitions, retimes, beat markers, cross-refs), where every cut point is defined as an absolute frame number that maps directly to NLEs or Remotion/AE code timelines.

skills/beat-sync-editing/SKILL.md
A good plan is renderer-agnostic and hands off to an NLE or a code timeline (`remotion-video`, `after-effects`):
The reference NLE↔code mapping table translates editing concepts (crossfade, ramp, J/L) into Remotion <Sequence>/<Audio> and AE layer/time-remap properties—delivering concrete numbers rather than subjective adjectives.

Forms a cohesive system with companion repository skills: motion personality (motion-art-direction) determines phrase lengths and transition families, animation-principles defines BPM-to-beat relationships, and this skill grounds them into frame-accurate cut points.

skills/beat-sync-editing/SKILL.md
**Motion Personality** (`motion-art-direction`) sets cut rhythm: the chosen energy maps straight to phrase length and transition family.
'Energetic → 1–2 beat climax / hard cuts / aggressive ramps; Premium → 8–16 beat long holds / hard cuts + occasional dissolves'—upstream stylistic parameters serve directly as inputs to this skill.

2Core Capabilities

01BPM-to-frame conversion and phrase grid generation (including JS example code for generating on-beat frame arrays)
02Eighth-grid subdivision (half-beat/sixteenth-note quick cuts, transient FX alignment)
03Cut-on-action/motion seam-hiding techniques (cutting mid-action, matching direction/velocity, cutting at peak transform)
04Motivated transition library: frame offsets and application scenarios for match cuts, J-cuts, L-cuts, and whip pans
05Speed ramp frame-by-frame recipe with motion blur/optical flow configurations (AE Pixel Motion / Remotion interpolate)
06Four-phase arc design and average shot length (ASL) curves
07Common mistakes reference table (8 symptoms → root causes → fixes: drift, frantic, jarring, strobe, flat, etc.)
08NLE-to-code timeline mapping (Remotion <Sequence>/<Audio>, AE time-remap / layer in-out points)

3External Dependencies

KindDependency / Endpoint
packageaubio / web-audio-beat-detector / tap-tempo（可选离线 BPM 检测，reference 建议项，非强制）

4Recommended Governance & Evidence

Suggested Controls for Safe Operation
For Agent Runtime
Can be auto-loaded
For Administrators
Register source and version
Evidence & Triggers (File Paths & Excerpts)
  • SKILL.md: Pure prompt-based instructions and rule texts; involves no script execution or external side effects.
Audit Notes: Purely an instructional and computational methodology: contains no script execution, no outbound network requests, no credential access, and no local file writes. Deliverables consist of frame numbers and parameter text (edit-timing plans) output directly in chat or written to host documentation. Optional offline BPM detection tools are merely reference recommendations rather than execution paths. The only operational considerations involve conversational alignment (aesthetic recommendations) and metadata accuracy (BPM and asset lengths), presenting no code-level security risks.

5Second-Pass Verification

  • [ok] 帧数学正确性抽查 — 多处公式与表格值复算一致（120BPM@30fps=15、128BPM@30fps=14.06、drop@beat32=frame450）；'round each cumulative beat' 与 ANTI-PATTERN 的 offset 提醒自洽。
  • [ok] 无执行/无外发反查 — 两文件无任何可执行命令；可选 BPM 检测工具仅出现在 reference 一句建议中，无强制调用路径。
  • [ok] 交叉引用可解析性 — motion-art-direction、animation-principles、remotion-video、after-effects 均在本 repo（与 motion-art-direction 页引用的外部 pack 不同，本页全部内聚）。
  • [ok] SKILL.md 与 reference 数值一致性 — J/L 偏移（4–12f / 12–24f）、ramp 配方（100→25→100%）、128BPM@30fps=14.06 f/beat 在两文件一致。
  • [ok] deliverable 验证闭环 — checklist 要求 'frame/fps against detected beat seconds' 由宿主/NLE 完成；skill 不自行检测音频，边界诚实。

6Verdict & Scenarios

  • Completely quantifies editing rhythm into frame numbers: BPM math + phrase grids + cumulative rounding to prevent drift, enabling direct generation of Remotion/AE timelines
  • Every transition and speed ramp includes explicit frame offsets and motivational rules, enforcing strong constraints against anti-patterns and defaulting to hard cuts
  • High instructional density featuring a three-part toolkit: worked examples, ANTI-PATTERN warnings, and an 8-row common mistakes troubleshooting table
  • Acts as the execution layer within the ecosystem, directly interfacing with numeric personality values from motion-art-direction
    • Best for: Ideal for editing planning workflows where footage/shots must sync to music, pacing needs tuning, or an edit plan must translate into exact Remotion, AE, or NLE frame numbers—especially when an AI agent needs to draft a timeline blueprint prior to assembly. Also serves well as instructional material for beginners learning editing rhythm.
    Not for: Not suitable for fine music editing that demands real-time acoustic feedback (the skill does not analyze raw audio and requires host tools for BPM detection); not intended for asset management or rough assembly organization workflows (focuses purely on rhythm design); not suited for unconventional styles requiring relentless cutting on every single beat (which the skill actively discourages).
    Install Agent-Ready
    ① Verified Mirror 2026-09-09
    Option A · Direct DownloadDownload beat-sync-editing.tar.gz
    sha256: 61e03294d1032082…
    Option B · Copy Guide for Agent
    install.json
    Agents automatically download and verify mirrors from this JSON guide.
    ② Upstream GitHub
    GitHub Repo ↗
    Pinned to commit 3c129f769d.