How to add a bulge and pinch with Claude

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.

#!/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")