How to add a long shadow text with Claude

Add long shadow text to input.mp4: the words "GLOW UP" in a heavy font (Arial Black) 13% of the frame width tall, flat yellow (255, 214, 0), centered 45% across and 14% down. Behind the letters draw a solid red (215, 35, 55) shadow, fully opaque with no blur, made by stamping the letter shapes 1 pixel at a time down and to the right at 45 degrees, so each letter extends into a long diagonal block. At 0.5 seconds the letters fade in over 0.15 seconds while the shadow stretches from 0 to its full length of 13% of the frame width (along each axis) over 0.8 seconds, easing out; then everything stays to the end. Use Python with Pillow to draw it and ffmpeg to put it on the video (don't rely on ffmpeg's drawtext filter), keep the audio, and save it as output.mp4.

#!/usr/bin/env python3
"""Long shadow text: flat yellow letters appear and a solid red shadow stretches out of them at 45 degrees.

Usage: python3 long-shadow-text.py input.mp4 output.mp4
Needs ffmpeg, Pillow and numpy (pip install pillow numpy).
"""
import json
import math
import subprocess
import sys
from functools import lru_cache
from pathlib import Path

import numpy as np
from PIL import Image, ImageDraw, ImageFont

TEXT = "GLOW UP"
START = 0.5                # second the letters appear
FADE = 0.15                # seconds the letters take to fade in
GROW = 0.8                 # seconds the shadow takes to stretch to full length
SIZE = 0.13                # letter height as a share of the frame width
X, Y = 0.45, 0.14          # text center (0-1 across and down the frame)
LENGTH = 0.13              # shadow length along each axis, as a share of the frame width
COLOR = (255, 214, 0)      # letter color
SHADOW = (215, 35, 55)     # shadow color, solid
FONTS = ["/System/Library/Fonts/Supplemental/Arial Black.ttf",    # macOS
         "/usr/share/fonts/truetype/dejavu/DejaVuSans-Bold.ttf",  # Linux
         "C:/Windows/Fonts/ariblk.ttf"]                           # Windows
FONT_FILE = next((f for f in FONTS if Path(f).exists()), None) or sys.exit("No bold font found: add one to FONTS")


def letters():
    """The text as a full-frame alpha mask (0-255)."""
    mask = Image.new("L", (w, h))
    font = ImageFont.truetype(FONT_FILE, round(w * SIZE))
    ImageDraw.Draw(mask).text((w * X, h * Y), TEXT, font=font, anchor="mm", fill=255)
    return np.asarray(mask)


@lru_cache(maxsize=None)
def shadow(steps):
    """The letters stamped 1 to `steps` pixels down and to the right: a solid 45-degree shadow."""
    out = np.zeros_like(text_mask)
    for i in range(1, steps + 1):
        np.maximum(out[i:, i:], text_mask[:-i, :-i], out=out[i:, i:])
    return out


def overlay(t):
    img = np.zeros((h, w, 4), np.uint8)
    if t < START:
        return img
    fade = min((t - START) / FADE, 1)
    grow = 1 - (1 - min((t - START) / GROW, 1)) ** 3   # ease out: fast, then settling
    s = shadow(round(grow * LENGTH * w)).astype(np.float32)
    letter = text_mask.astype(np.float32)
    alpha = np.maximum(s, letter) / 255
    for c in range(3):   # letters on top of the shadow
        img[..., c] = (SHADOW[c] * (1 - letter / 255) + COLOR[c] * letter / 255).astype(np.uint8)
    img[..., 3] = (alpha * fade * 255).astype(np.uint8)
    return img


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


def render(src, out):
    """Draw overlay(t) on every frame of src and save to out, keeping the audio."""
    ff = subprocess.Popen(["ffmpeg", "-y", "-v", "error", "-i", src,
                           "-f", "rawvideo", "-pix_fmt", "rgba", "-s", f"{w}x{h}", "-r", rate, "-i", "-",
                           "-filter_complex", "[0:v][1:v]overlay=shortest=1,format=yuv420p[v]",
                           "-map", "[v]", "-map", "0:a?", "-c:v", "libx264", "-crf", "18", "-c:a", "copy", out],
                          stdin=subprocess.PIPE)
    for i in range(math.ceil(duration * fps)):
        ff.stdin.write(overlay(i / fps).tobytes())
    ff.stdin.close()
    if ff.wait():
        sys.exit("ffmpeg failed")


src, out = sys.argv[1:3]
w, h, rate, fps, duration = probe(src)
text_mask = letters()
render(src, out)