--- title: "How to add a twirl with Claude (tested prompt and script)" description: "At 1 second the bottle winds into a purple-and-cream spiral curled around its label while the acrylic block below and the backdrop above stay still, holds for a second, then unwinds back into a bottle by 4.5 seconds. Install one skill and ask Claude Code, or run the Python script we tested yourself." url: https://www.recharm.com/effects/twirl-swirl --- # How to add a twirl with Claude At 1 second the bottle winds into a purple-and-cream spiral curled around its label while the acrylic block below and the backdrop above stay still, holds for a second, then unwinds back into a bottle by 4.5 seconds. 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 twirl to input.mp4 Twirl center, as shares across and down the frame: 0.5, 0.52 Twirl radius as a share of the frame width; nothing outside it moves: 0.45 ``` ## 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 twirl 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 | | -------- | ----------- | ---------------------------------------------------------------------------------- | | `X, Y` | `0.5, 0.52` | Twirl center, as shares across and down the frame. | | `RADIUS` | `0.45` | Twirl radius as a share of the frame width; nothing outside it moves. | | `TWIST` | `720` | Degrees the very center turns at full twirl; the turn fades to nothing at the rim. | | `START` | `1.0` | Second the twirl starts winding up. | | `WIND` | `1.5` | Seconds to wind up to full twist. | | `HOLD` | `1.0` | Seconds held at full twist. | | `UNWIND` | `1.0` | Seconds to unwind back to the plain picture. | ## Without the skill Don’t want to install the skill? Paste this prompt into Claude Code and Claude writes the script itself. ``` Add a twirl effect to input.mp4 with Python, OpenCV (cv2.remap) and numpy, and ffmpeg for reading and writing the video. Twirl a circle of radius 243 px (45% of the 540 px width) centered at x = 270, y = 499 (50% across, 52% down). For each output pixel at distance r and angle theta from that center, sample the input at the same distance and angle theta + A * (1 - r/243)^2 (bilinear), so the center turns by A and the turn fades to nothing at the rim; pixels outside the circle are left exactly as they are. A, in degrees, follows a smoothstep ease (s(p) = p*p*(3-2p), p clamped to 0-1): 0 before 1.0 s, rising to 720 from 1.0 to 2.5 s (A = 720*s((t-1)/1.5)), held at 720 from 2.5 to 3.5 s, falling back to 0 from 3.5 to 4.5 s (A = 720*(1 - s(t-3.5))), and 0 after 4.5 s. Leave the frames untouched whenever A is 0. Keep the size (540x960), frame rate (30fps), 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 `twirl-swirl.py` and run: ``` python3 twirl-swirl.py input.mp4 output.mp4 ``` ``` #!/usr/bin/env python3 """Twirl: a round patch of the picture centered on the bottle winds into a spiral, holds, then unwinds. Usage: python3 twirl-swirl.py input.mp4 output.mp4 Needs ffmpeg, OpenCV and numpy (pip install opencv-python-headless numpy). """ import json import math import subprocess import sys import cv2 import numpy as np X, Y = 0.5, 0.52 # twirl center (0-1 across and down the frame) RADIUS = 0.45 # twirl radius as a share of the frame width; outside it nothing moves TWIST = 720 # degrees the very center turns at full twirl; the turn fades to nothing at the rim START = 1.0 # second the twirl starts winding up WIND = 1.5 # seconds to wind up to full twist HOLD = 1.0 # seconds held at full twist UNWIND = 1.0 # seconds to unwind back to the plain picture def ease(p): p = min(max(p, 0), 1) return p * p * (3 - 2 * p) def twist_at(t): """Degrees the center is turned at second t: wind up, hold, unwind, each eased.""" if t < START + WIND + HOLD: return TWIST * ease((t - START) / WIND) return TWIST * (1 - ease((t - START - WIND - HOLD) / UNWIND)) def twirled(img, degrees): """Each pixel inside the circle samples the input turned by `degrees` * (1 - distance/radius)^2.""" phi = theta + math.radians(degrees) * falloff return cv2.remap(img, (cx + r * np.cos(phi)).astype(np.float32), (cy + r * np.sin(phi)).astype(np.float32), cv2.INTER_LINEAR, borderMode=cv2.BORDER_REFLECT) 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) src, out = sys.argv[1:3] w, h, rate, fps = probe(src) # polar coordinates of every pixel around the twirl center, worked out once cx, cy, radius = X * w, Y * h, RADIUS * w ys, xs = np.mgrid[0:h, 0:w].astype(np.float32) r, theta = np.hypot(xs - cx, ys - cy), np.arctan2(ys - cy, xs - cx) falloff = np.clip(1 - r / radius, 0, 1) ** 2 reader = subprocess.Popen(["ffmpeg", "-v", "error", "-i", src, "-f", "rawvideo", "-pix_fmt", "rgb24", "-"], stdout=subprocess.PIPE) writer = subprocess.Popen(["ffmpeg", "-y", "-v", "error", "-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 frame = np.frombuffer(raw, np.uint8).reshape(h, w, 3) degrees = twist_at(i / fps) if degrees > 0: frame = twirled(frame, degrees) writer.stdin.write(frame.tobytes()) i += 1 writer.stdin.close() if reader.wait() or writer.wait(): sys.exit("ffmpeg failed") ``` ## More distortion and glitch - [Anaglyph 3D **Anaglyph 3D**](https://www.recharm.com/effects/anaglyph-3d) - [Black hole **Black hole**](https://www.recharm.com/effects/black-hole) - [Bulge and pinch **Bulge and pinch**](https://www.recharm.com/effects/bulge-pinch) - [Datamosh **Datamosh**](https://www.recharm.com/effects/datamosh) - [Disintegration **Disintegration**](https://www.recharm.com/effects/disintegration) ## 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)