How to add a typewriter text with Claude

Add a typewriter text effect to input.mp4: the line "3 reasons this serum sold out" types out from 0.3 seconds at 14 characters per second, white bold text with a black outline, left-aligned near the top, with a blinking cursor after the last letter. 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
"""Typewriter text: a line of text types itself out letter by letter, with a cursor at the end.

Usage: python3 typewriter-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, ImageFont

TEXT = "3 reasons this serum sold out"
START = 0.3      # second the typing starts
CPS = 14         # characters typed per second
SIZE = 0.075     # text height as a share of the frame width
TOP = 0.12       # top of the text block (0 = top of the frame)
MARGIN = 0.08    # left and right margin, as a share of the frame width
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 wrap(text, font, width):
    """Split text into lines that fit, decided once for the whole text so lines don't jump while typing."""
    lines, line = [], ""
    for word in text.split():
        trial = f"{line} {word}".strip()
        if font.getlength(trial) <= width or not line:
            line = trial
        else:
            lines.append(line)
            line = word
    return lines + [line]


def overlay(t):
    img = Image.new("RGBA", (w, h))
    draw = ImageDraw.Draw(img)
    shown = max(0, int((t - START) * CPS))
    y = h * TOP
    for line in lines:
        part = line[:max(shown, 0)]  # lines not reached yet stay empty
        shown -= len(line) + 1
        draw.text((w * MARGIN, y), part, font=font, fill="white", stroke_width=round(w * 0.008), stroke_fill="black")
        if 0 >= shown > -len(line) - 1 and int(t * 2) % 2 == 0 and t >= START:  # blinking cursor after the last letter
            x = w * MARGIN + font.getlength(part) + 4
            draw.rectangle([x, y + font.size * 0.1, x + font.size * 0.12, y + font.size * 1.05], fill="white")
        y += font.size * 1.25
    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)
font = ImageFont.truetype(FONT_FILE, round(w * SIZE))
lines = wrap(TEXT, font, w * (1 - 2 * MARGIN))
render(src, out)