--- title: "How to add a color pulse on beat with Claude (tested prompt and script)" description: "On every kick drum the purple serum bottle flushes hot pink and the holographic backdrop turns rosier and more vivid, then the colors drain back to normal within 0.3 seconds, twice a second with the 120 BPM loop. Install one skill and ask Claude Code, or run the Python script we tested yourself." url: https://www.recharm.com/effects/color-pulse-on-beat --- # How to add a color pulse on beat with Claude On every kick drum the purple serum bottle flushes hot pink and the holographic backdrop turns rosier and more vivid, then the colors drain back to normal within 0.3 seconds, twice a second with the 120 BPM loop. Made by the script on this page, from our own test clip. ## Get this effect 1. ### Switch to Code in your [Claude Desktop App](https://claude.com/download) 2. ### Install the skill (once) ``` Install the Recharm video effects skill: download https://recharm-growth-staging.s3.us-east-2.amazonaws.com/website/downloads/recharm-video-effects.zip and unzip it into ~/.claude/skills ``` 3. ### Ask for the effect ``` Add a color pulse on beat to input.mp4 Degrees the colors turn round the color wheel on a beat: 60 Color strength right on a beat: 1.8 ``` ## Several videos, several effects, one ask Put your clips in the folder, mention them with @, and ask for everything at once. Claude runs one tested script after another on each clip, then joins them. Add a color pulse on beat to **@clip1.mp4**, put a sale badge on **@clip2.mp4**, give **@clip3.mp4** a VHS look, then join all three with crossfades. ## Settings you can change Ask Claude to change any of these, or edit them at the top of the script. | Setting | Default | What it does | | ------------ | ------- | ------------------------------------------------------------------------------------- | | `HUE_SHIFT` | `60` | Degrees the colors turn round the color wheel on a beat. 60 takes purple to hot pink. | | `SATURATION` | `1.8` | Color strength right on a beat. 1 leaves it unchanged. | | `FADE` | `0.3` | Seconds to fade back to the original colors after each beat. | | `BASS_HZ` | `150` | Beats are found in the sound below this frequency, where the kick drum sits. | | `RATE` | `22050` | Audio sample rate the beat tracking uses. | | `HOP` | `256` | Audio samples per analysis step. Smaller gives more exact beat times. | ## Without the skill Don’t want to install the skill? Paste this prompt into Claude Code and Claude writes the script itself. ``` Add a color pulse on the beat to input.mp4. Find the kick drum beats with librosa: take the onset strength of the audio (mono, 22050 Hz) with hop_length 256, fmax 150 Hz and n_mels 8, run librosa.beat.beat_track on that envelope, move each beat back to where its hit starts with librosa.onset.onset_backtrack, convert to seconds and round each to the nearest video frame. For every frame work out a pulse amount a = (1 - p)^2, where p is the seconds since the latest beat divided by 0.3 (a = 0 once 0.3 seconds have passed, and before the first beat). Convert the frame to HSV in floating point (OpenCV, hue 0-360), add 60 x a degrees to the hue (wrapping at 360), multiply the saturation by 1 + 0.8 x a (so 1.8x right on a beat, clipped to 1), keep the brightness, and convert back. The purple bottle should turn hot pink on each beat and look untouched between beats. No text is needed; if you add any, draw it with Pillow, not ffmpeg's drawtext. Keep the size (540x960), 30fps, the 6-second length and the audio, encode H.264 yuv420p, and save it as output.mp4. ``` ## Run it without Claude This is the exact script we tested. Save it as `color-pulse-on-beat.py` and run: ``` python3 color-pulse-on-beat.py input.mp4 output.mp4 ``` ``` #!/usr/bin/env python3 """Color pulse on beat: on every kick drum the colors swing round the color wheel and surge in saturation, then fade back. Usage: python3 color-pulse-on-beat.py input.mp4 output.mp4 (the input needs a music track with a beat) Needs ffmpeg, librosa, numpy and OpenCV (pip install librosa numpy opencv-python-headless). """ import json import subprocess import sys import cv2 import librosa import numpy as np HUE_SHIFT = 60 # degrees the colors turn round the color wheel on a beat (60 takes purple to hot pink) SATURATION = 1.8 # color strength on a beat (1 = unchanged) FADE = 0.3 # seconds to fade back to the original colors after each beat BASS_HZ = 150 # beats are found in the sound below this frequency (the kick drum) RATE = 22050 # audio sample rate the beat tracking uses HOP = 256 # audio samples per analysis step (smaller = more exact beat times) def probe(path): info = json.loads(subprocess.check_output(["ffprobe", "-v", "error", "-select_streams", "v:0", "-show_entries", "stream=width,height,r_frame_rate", "-of", "json", path])) s = info["streams"][0] num, den = s["r_frame_rate"].split("/") return s["width"], s["height"], s["r_frame_rate"], float(num) / float(den) def beat_times(src): """Kick drum beats in seconds: track the beat in the bass, then move each one back to where its hit starts.""" pcm = subprocess.check_output(["ffmpeg", "-v", "error", "-i", src, "-ac", "1", "-ar", str(RATE), "-f", "f32le", "-"]) audio = np.frombuffer(pcm, np.float32) bass = librosa.onset.onset_strength(y=audio, sr=RATE, hop_length=HOP, fmax=BASS_HZ, n_mels=8) _, beats = librosa.beat.beat_track(onset_envelope=bass, sr=RATE, hop_length=HOP) beats = librosa.onset.onset_backtrack(beats, bass) return librosa.frames_to_time(beats, sr=RATE, hop_length=HOP) def pulse_at(t, beats): """1 right on a beat, fading out to 0 over FADE seconds.""" past = beats[beats <= t + 1e-6] if not len(past) or t - past[-1] >= FADE: return 0.0 return (1 - (t - past[-1]) / FADE) ** 2 def recolor(img, amount): """Turn the hue by HUE_SHIFT and raise the saturation to SATURATION, both scaled by amount (0-1).""" hsv = cv2.cvtColor(img.astype(np.float32) / 255, cv2.COLOR_RGB2HSV) # hue 0-360, saturation 0-1 hsv[..., 0] = (hsv[..., 0] + HUE_SHIFT * amount) % 360 hsv[..., 1] = np.clip(hsv[..., 1] * (1 + (SATURATION - 1) * amount), 0, 1) return (cv2.cvtColor(hsv, cv2.COLOR_HSV2RGB) * 255).round().astype(np.uint8) src, out = sys.argv[1], sys.argv[2] w, h, rate, fps = probe(src) beats = np.round(beat_times(src) * fps) / fps # line each beat up with a video frame reader = subprocess.Popen(["ffmpeg", "-v", "error", "-i", src, "-f", "rawvideo", "-pix_fmt", "rgb24", "-"], stdout=subprocess.PIPE) writer = subprocess.Popen(["ffmpeg", "-v", "error", "-y", "-f", "rawvideo", "-pix_fmt", "rgb24", "-s", f"{w}x{h}", "-r", rate, "-i", "-", "-i", src, "-map", "0:v", "-map", "1:a?", "-c:v", "libx264", "-crf", "18", "-pix_fmt", "yuv420p", "-c:a", "copy", "-shortest", out], stdin=subprocess.PIPE) i = 0 while True: raw = reader.stdout.read(w * h * 3) if len(raw) < w * h * 3: break img = np.frombuffer(raw, np.uint8).reshape(h, w, 3) amount = pulse_at(i / fps, beats) writer.stdin.write(recolor(img, amount).tobytes() if amount else img.tobytes()) i += 1 writer.stdin.close() reader.wait() sys.exit(writer.wait()) ``` ## More music-synced visuals - [AI voice orb **AI voice orb**](https://www.recharm.com/effects/ai-voice-orb) - [Audio-reactive blob **Audio-reactive blob**](https://www.recharm.com/effects/audio-reactive-blob) - [Audio-reactive particles **Audio-reactive particles**](https://www.recharm.com/effects/audio-reactive-particles) - [Audio-reactive text **Audio-reactive text**](https://www.recharm.com/effects/audio-reactive-text) - [Audio waveform **Audio waveform**](https://www.recharm.com/effects/audio-waveform) ## Find 3x _winning ads_ Recharm cuts your ad footage into tagged, searchable clips: hooks, testimonials, product shots. Find the shots that win, add the effect with Claude, and ship 3x more ad edits. [Start 14-day free trial](https://www.recharm.com/get-started)