--- title: "How to add a bulge and pinch with Claude (tested prompt and script)" description: "The middle of the serum bottle swells out like a fishbowl until its label bows round, then sucks in to an hourglass waist before springing back to its normal shape. Install one skill and ask Claude Code, or run the Python script we tested yourself." url: https://www.recharm.com/effects/bulge-pinch --- # How to add a bulge and pinch with Claude The middle of the serum bottle swells out like a fishbowl until its label bows round, then sucks in to an hourglass waist before springing back to its normal shape. 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 bulge and pinch to input.mp4 Center of the patch, as shares of the frame's width and height: 0.50, 0.58 Patch radius as a share of the frame width: 0.40 ``` ## 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 bulge and pinch 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` | `0.50, 0.58` | Center of the patch, as shares of the frame's width and height. | | `RADIUS` | `0.40` | Patch radius as a share of the frame width. | | `AMOUNT` | `0.5` | How strong the warp is: 0.5 shows the center 2x bigger in the bulge and 1.5x smaller in the pinch. | | `KEYS` | `(0.8, 0), (1.5, 1), (2.5, 1), (3.3, -1), (4.3, -1), (5.0, 0)` | Seconds and strength: 1 is a full bulge, -1 a full pinch, 0 no warp. | ## Without the skill Don’t want to install the skill? Paste this prompt into Claude Code and Claude writes the script itself. ``` Add a bulge-and-pinch distortion to input.mp4 with Python, numpy and OpenCV, using ffmpeg to read and write the frames. Work on a round patch centered 50% across and 58% down the frame with a radius of 40% of the frame width (216 px on a 540-wide frame); nothing outside it moves. For each output pixel at offset (dx, dy) from that center and distance d, sample the input at center + (dx, dy) * (1 - s * 0.5 * max(0, 1 - d^2 / radius^2)^2) with cv2.remap (cubic), so with s = 1 the center shows 2x bigger (bulge) and with s = -1 it shows 1.5x smaller (pinch), easing to no change at the rim. Animate s with smoothstep easing between these keys: 0 at 0.8 seconds, 1 at 1.5, 1 at 2.5, -1 at 3.3, -1 at 4.3, 0 at 5.0; leave the video untouched before 0.8 and after 5.0 seconds. There's no text to draw, but if you add any, draw it with Pillow, not ffmpeg's drawtext. Keep the audio and save it as output.mp4 at 30fps, same size as the input. ``` ## Run it without Claude This is the exact script we tested. Save it as `bulge-pinch.py` and run: ``` python3 bulge-pinch.py input.mp4 output.mp4 ``` ``` #!/usr/bin/env python3 """Bulge and pinch: a round patch over the bottle swells out like a fishbowl, then sucks in to a pinch and springs back. Usage: python3 bulge-pinch.py input.mp4 output.mp4 Needs ffmpeg, OpenCV and numpy (pip install opencv-python-headless numpy). """ import json import subprocess import sys import cv2 import numpy as np X, Y = 0.50, 0.58 # center of the patch (0-1 across and down the frame) RADIUS = 0.40 # patch radius as a share of the frame width; nothing outside it moves AMOUNT = 0.5 # 0.5 = the center shows 2x bigger when bulged and 1.5x smaller when pinched KEYS = [(0.8, 0), (1.5, 1), (2.5, 1), (3.3, -1), (4.3, -1), (5.0, 0)] # (second, strength): 1 bulge, -1 pinch def strength(t): """Strength at time t, eased (smoothstep) between the KEYS, 0 before the first and after the last.""" for (t0, s0), (t1, s1) in zip(KEYS, KEYS[1:]): if t0 <= t < t1: u = (t - t0) / (t1 - t0) return s0 + (s1 - s0) * u * u * (3 - 2 * u) return 0.0 def source_map(s): """For every pixel, the input pixel it shows. Inside the patch each pixel is pulled toward the center (bulge, s > 0) or pushed away from it (pinch, s < 0), most at the center and not at all at the rim.""" falloff = np.clip(1 - dist2 / (r * r), 0, None) ** 2 scale = 1 - s * AMOUNT * falloff return (cx + dx * scale).astype(np.float32), (cy + dy * scale).astype(np.float32) 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) rows, cols = np.mgrid[0:h, 0:w].astype(np.float32) cx, cy, r = X * w, Y * h, RADIUS * w dx, dy = cols - cx, rows - cy dist2 = dx * dx + dy * dy 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: buf = reader.stdout.read(w * h * 3) if len(buf) < w * h * 3: break img = np.frombuffer(buf, np.uint8).reshape(h, w, 3) s = strength(i / fps) if s: map_x, map_y = source_map(s) img = cv2.remap(img, map_x, map_y, cv2.INTER_CUBIC, borderMode=cv2.BORDER_REFLECT) writer.stdin.write(img.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) - [Datamosh **Datamosh**](https://www.recharm.com/effects/datamosh) - [Disintegration **Disintegration**](https://www.recharm.com/effects/disintegration) - [Drunk vision **Drunk vision**](https://www.recharm.com/effects/drunk-vision) ## 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)