How to add a fade-in text with Claude

Add fade-in text to input.mp4: "Glow in 7 days" in bold white (255, 255, 255), 70 pixels tall (13% of the frame width), centered horizontally 12% of the way down, with a soft dark plum (40, 20, 60) shadow 3 pixels below it blurred by 5 pixels. It's invisible until 0.8 seconds, fades in linearly to full opacity by 1.6 seconds, holds until 3.6 seconds, then fades out linearly to nothing by 4.4 seconds. 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
"""Fade-in text: a white headline fades up from nothing, holds, then fades back out.

Usage: python3 fade-in-text.py input.mp4 output.mp4
Needs ffmpeg and Pillow (pip install pillow).
"""
import json
import math
import subprocess
import sys
from pathlib import Path

from PIL import Image, ImageDraw, ImageFilter, ImageFont

TEXT = "Glow in 7 days"     # the headline
START = 0.8                 # second the fade in starts
FADE = 0.8                  # seconds each fade takes
HOLD = 2.0                  # seconds the text stays fully visible
Y = 0.12                    # text center, 0-1 down the frame
SIZE = 0.13                 # text height as a share of the frame width
COLOR = (255, 255, 255)     # text color
FONTS = ["/System/Library/Fonts/Supplemental/Arial Bold.ttf",     # macOS
         "/usr/share/fonts/truetype/dejavu/DejaVuSans-Bold.ttf",  # Linux
         "C:/Windows/Fonts/arialbd.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 headline():
    """The text with a soft dark shadow behind it, on a transparent frame."""
    img = Image.new("RGBA", (w, h))
    font = ImageFont.truetype(FONT_FILE, round(w * SIZE))
    shadow = Image.new("RGBA", (w, h))
    ImageDraw.Draw(shadow).text((w / 2, h * Y + 3), TEXT, font=font, anchor="mm", fill=(40, 20, 60, 230))
    img.alpha_composite(shadow.filter(ImageFilter.GaussianBlur(5)))
    ImageDraw.Draw(img).text((w / 2, h * Y), TEXT, font=font, anchor="mm", fill=COLOR)
    return img


def opacity(t):
    """0 before START, up to 1 over FADE, 1 for HOLD, back down to 0 over FADE."""
    return min(max((t - START) / FADE, 0), 1, max((START + 2 * FADE + HOLD - t) / FADE, 0))


def overlay(t):
    a = opacity(t)
    if a <= 0:
        return blank
    img = text.copy()
    img.putalpha(text.getchannel("A").point(lambda v: round(v * a)))
    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 = headline()
blank = Image.new("RGBA", (w, h))
render(src, out)