--- title: "How to add a handwriting animation with Claude (tested prompt and script)" description: "\"Pure glow\" writes itself across the top in deep violet handwriting, letter by letter from left to right, as if an unseen pen were inking it. Install one skill and ask Claude Code, or run the Python script we tested yourself." url: https://www.recharm.com/effects/handwriting-animation --- # How to add a handwriting animation with Claude "Pure glow" writes itself across the top in deep violet handwriting, letter by letter from left to right, as if an unseen pen were inking it. Made by the script on this page, from our own test clip. ## Get this effect 1. ### Switch to Code in your [Claude Desktop App](https://claude.com/download) 2. ### Install the skill (once) ``` Install the Recharm video effects skill: download https://recharm-growth-staging.s3.us-east-2.amazonaws.com/website/downloads/recharm-video-effects.zip and unzip it into ~/.claude/skills ``` 3. ### Ask for the effect ``` Add a handwriting animation to input.mp4 Text: Pure glow ``` ## Several videos, several effects, one ask Put your clips in the folder, mention them with @, and ask for everything at once. Claude runs one tested script after another on each clip, then joins them. Add a handwriting animation to **@clip1.mp4**, put a sale badge on **@clip2.mp4**, give **@clip3.mp4** a VHS look, then join all three with crossfades. ## Settings you can change Ask Claude to change any of these, or edit them at the top of the script. | Setting | Default | What it does | | ------- | -------------- | -------------------------------------------------------------------------- | | `TEXT` | `Pure glow` | What gets written. | | `START` | `0.5` | Second the pen starts writing. | | `WRITE` | `2.0` | Seconds the whole line takes to write. | | `SIZE` | `0.20` | Font size as a share of the frame width. | | `Y` | `0.12` | Where the line's center sits (0 = top, 1 = bottom). | | `COLOR` | `(35, 20, 75)` | Ink color. | | `SLANT` | `0.3` | Lean of the pen's leading edge, to match the font's slant. | | `LIFT` | `0.1` | Time to cross a gap between letters, as a share of writing the same width. | ## Without the skill Don’t want to install the skill? Paste this prompt into Claude Code and Claude writes the script itself. ``` Add a handwriting animation to input.mp4: the words "Pure glow" in Bradley Hand Bold (or any handwriting font), font size 20% of the frame width, deep violet ink (35, 20, 75), centered across with the line's center 12% of the way down. The text writes itself on from left to right as if an unseen pen were drawing it, starting at 0.5 seconds and finishing at 2.5 seconds: reveal it with a mask whose leading edge leans to the right like the handwriting (0.3 pixels across per pixel up) and is softened over 3% of the line's width, moving at a steady pace through the letters and crossing the gap between the words in a tenth of the time. Nothing shows before 0.5 seconds, and the finished words stay to the end. Use Python with Pillow to draw the text 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. ``` ## Run it without Claude This is the exact script we tested. Save it as `handwriting-animation.py` and run: ``` python3 handwriting-animation.py input.mp4 output.mp4 ``` ``` #!/usr/bin/env python3 """Handwriting animation: a line of script writes itself on, left to right, as if an unseen pen were drawing it. Usage: python3 handwriting-animation.py input.mp4 output.mp4 Needs ffmpeg, Pillow and numpy (pip install pillow numpy). """ import json import math import subprocess import sys from pathlib import Path import numpy as np from PIL import Image, ImageDraw, ImageFont TEXT = "Pure glow" # what gets written START = 0.5 # second the pen starts writing WRITE = 2.0 # seconds the whole line takes to write SIZE = 0.20 # font size as a share of the frame width Y = 0.12 # where the line's center sits (0 = top, 1 = bottom) COLOR = (35, 20, 75) # ink color, a deep violet SLANT = 0.3 # lean of the pen's leading edge, matching the script's slant LIFT = 0.1 # time to cross a gap between letters, as a share of writing the same width EDGE = 0.03 # soft edge where the ink is still going on, as a share of the line FONTS = ["/System/Library/Fonts/Supplemental/Bradley Hand Bold.ttf", # macOS "/usr/share/fonts/truetype/dejavu/DejaVuSerif-BoldItalic.ttf", # Linux "C:/Windows/Fonts/segoesc.ttf"] # Windows (Segoe Script) FONT_FILE = next((f for f in FONTS if Path(f).exists()), None) or sys.exit("No script font found: add one to FONTS") def written_line(): """The finished line in full, centered across the frame.""" img = Image.new("RGBA", (w, h)) ImageDraw.Draw(img).text((w / 2, h * Y), TEXT, font=ImageFont.truetype(FONT_FILE, round(w * SIZE)), anchor="mm", fill=COLOR) return img def pen_order(line): """When the pen reaches each pixel, 0 at the first stroke to 1 at the last. It moves left to right with its leading edge leaned like the handwriting, slows where there's ink and hops across the gaps between letters.""" ys, xs = np.mgrid[0:h, 0:w] u = np.round(xs + (h * Y - ys) * SLANT).astype(int) u -= u.min() ink = np.bincount(u[np.array(line.getchannel("A")) > 0], minlength=u.max() + 1) effort = np.where(ink > 0, 1.0, LIFT) effort[:np.argmax(ink > 0)] = 0 # nothing to write before the first stroke path = np.cumsum(effort) return path[u] / path[-1] def overlay(t): p = min(max((t - START) / WRITE, 0), 1) if p == 0: return blank reveal = np.clip((p * (1 + EDGE) - order) / EDGE, 0, 1) frame = line_rgba.copy() frame[..., 3] = (frame[..., 3] * reveal).astype(np.uint8) return Image.fromarray(frame) 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) line = written_line() line_rgba = np.array(line) order = pen_order(line) blank = Image.new("RGBA", (w, h)) render(src, out) ``` ## More captions and text - [AI chat reply animation **AI chat reply animation**](https://www.recharm.com/effects/ai-chat-typing) - [Animated bar chart **Animated bar chart**](https://www.recharm.com/effects/animated-bar-chart) - [Animated checklist **Animated checklist**](https://www.recharm.com/effects/animated-checklist) - [Animated line graph **Animated line graph**](https://www.recharm.com/effects/animated-line-graph) - [Animated pie chart **Animated pie chart**](https://www.recharm.com/effects/animated-pie-chart) ## Find 3x _winning ads_ Recharm cuts your ad footage into tagged, searchable clips: hooks, testimonials, product shots. Find the shots that win, add the effect with Claude, and ship 3x more ad edits. [Start 14-day free trial](https://www.recharm.com/get-started)