How to add a squeeze transition with Claude

Join clipA.mp4 and clipB.mp4 with a 0.6 second squeeze transition that starts 0.6 seconds before A ends. On each transition frame, with progress p going from 0 to 1 and eased e = p*p*(3-2p), squash the whole of A's frame (not a crop) into the top (1-e) of the frame height, full width, and squash the whole of B's frame into the remaining bottom e of the height, so at the halfway point A fills the top half and B the bottom half, each squeezed to half height. No gap, border, fade or black between them. Before the transition A plays normally; after it B plays full frame. Crossfade the audio over the same 0.6 seconds. Fit B to A's size first. The output is 11.4 seconds at 30fps, 540x960. Use ffmpeg with Python (numpy and Pillow for the per-frame resizing), keep the audio and save it as output.mp4.

#!/usr/bin/env python3
"""Squeeze transition: over 0.6s clip A squashes up into a thin strip at the top while clip B stretches up from the bottom to fill the frame.

Usage: python3 squeeze-transition.py clipA.mp4 clipB.mp4 output.mp4  (both clips need an audio track)
Needs ffmpeg, numpy and Pillow (pip install numpy pillow).
"""
import json
import subprocess
import sys
from itertools import islice

import numpy as np
from PIL import Image

D = 0.6    # transition length in seconds
FPS = 30   # output frame rate


def probe(path):
    info = json.loads(subprocess.check_output(["ffprobe", "-v", "error", "-select_streams", "v:0", "-show_entries",
                                               "stream=width,height:format=duration", "-of", "json", path]))
    return info["streams"][0]["width"], info["streams"][0]["height"], float(info["format"]["duration"])


def frames(path):
    """Decode a clip as w x h RGB frames at FPS, cropping it to fill the frame if its shape differs."""
    ff = subprocess.Popen(["ffmpeg", "-v", "error", "-i", path, "-vf",
                           f"scale={w}:{h}:force_original_aspect_ratio=increase,crop={w}:{h},fps={FPS}",
                           "-f", "rawvideo", "-pix_fmt", "rgb24", "-"], stdout=subprocess.PIPE)
    while True:
        data = ff.stdout.read(w * h * 3)
        if len(data) < w * h * 3:
            return
        yield np.frombuffer(data, np.uint8).reshape(h, w, 3)


def squeeze(a, b, p):
    """One transition frame at progress p (0-1): A squashed into the top, B stretched into the rest."""
    eased = p * p * (3 - 2 * p)       # smoothstep: starts and ends gently
    split = round(h * (1 - eased))    # rows A keeps; B fills the rest
    img = np.empty_like(a)
    if split:
        img[:split] = np.asarray(Image.fromarray(a).resize((w, split), Image.BICUBIC))
    if split < h:
        img[split:] = np.asarray(Image.fromarray(b).resize((w, h - split), Image.BICUBIC))
    return img


A, B, out = sys.argv[1:4]
w, h, length = probe(A)
cut_in = round((length - D) * FPS)   # first frame of the transition
n = round(D * FPS)                   # frames in the transition

enc = subprocess.Popen(["ffmpeg", "-y", "-v", "error", "-f", "rawvideo", "-pix_fmt", "rgb24", "-s", f"{w}x{h}",
                        "-r", str(FPS), "-i", "-", "-i", A, "-i", B,
                        "-filter_complex", f"[1:a][2:a]acrossfade=d={D}[au]", "-map", "0:v", "-map", "[au]",
                        "-c:v", "libx264", "-crf", "18", "-pix_fmt", "yuv420p", "-c:a", "aac", out],
                       stdin=subprocess.PIPE)
clip_a, clip_b = frames(A), frames(B)
for a in islice(clip_a, cut_in):
    enc.stdin.write(a.tobytes())
for i, (a, b) in enumerate(zip(islice(clip_a, n), islice(clip_b, n))):
    enc.stdin.write(squeeze(a, b, i / n).tobytes())
for b in clip_b:
    enc.stdin.write(b.tobytes())
enc.stdin.close()
if enc.wait():
    sys.exit("ffmpeg failed")