Beat-Synced Montage — a Claude skill

Drop in a folder of video clips and a song, get back a montage cut on the beat — every hard cut lands on the music. The tempo is detected from the song itself; no tapping, no timeline, no editing app.

No npm. No pip installs. Just ffmpeg + Python 3.

Quick start

python3 scripts/beat_montage.py --clips ./clips --music song.mp3 --out montage.mp4

Hear what tempo it detects first (renders nothing):

python3 scripts/beat_montage.py --clips ./clips --music song.mp3 --analyze

No royalty-free track handy? Make one from pure math:

python3 scripts/synth_track.py --bpm 128 --secs 30 --out track.wav

Why the cuts actually land

• The kick drives the grid — beat detection weights the low end, so the grid locks to the drum, not the vocals.
• Sub-frame tempo fit — the beat period is refined across the whole track, so cuts don't drift by the end.
• Half-a-frame A/V lock — shot lengths are quantized cumulatively; measured on the demo: every cut within one frame of the grid (mean error 8 ms).
• --pattern is the taste knob — 2,2,1,1 cuts two longer shots then two quick hits, so it feels edited, not metronomic.

Options

See SKILL.md for the full flag reference and troubleshooting.

Install as a Claude skill

Copy this folder into your Claude skills directory (e.g. ~/.claude/skills/beat-synced-montage/), then ask Claude to "cut these clips to this song."

Requirements

• ffmpeg + ffprobe on PATH
• Python 3.12+ (standard library only)

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Part of the Dunham Motion Skills series — free craft skills for people new to Claude.