--- title: "How to add a laser beam with Claude (tested prompt and script)" description: "A red laser fires in from the left edge, its glowing tip racing across the frame past the bottle's neck in a quarter second, then the white-hot beam hangs there flickering before it fades. Install one skill and ask Claude Code, or run the Python script we tested yourself." url: https://www.recharm.com/effects/laser-beam --- # How to add a laser beam with Claude A red laser fires in from the left edge, its glowing tip racing across the frame past the bottle's neck in a quarter second, then the white-hot beam hangs there flickering before it fades. 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 laser beam to input.mp4 Where the beam enters and leaves, as shares across and down the frame: (0.0, 0.30), (1.0, 0.42) Second the beam fires, and how many seconds its tip takes to cross the frame: 1.0, 0.25 ``` ## 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 laser beam 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 | | ------------------------ | -------------------------------- | ----------------------------------------------------------------------------- | | `FROM, TO` | `(0.0, 0.30), (1.0, 0.42)` | Where the beam enters and leaves, as shares across and down the frame. | | `START, SHOOT` | `1.0, 0.25` | Second the beam fires, and how many seconds its tip takes to cross the frame. | | `END, FADE` | `3.0, 0.4` | Second it has faded out by, and how many seconds the fade takes. | | `CORE, HALO` | `2.5, 14` | Half-widths in pixels of the white-hot core and the red glow around it. | | `CORE_COLOR, HALO_COLOR` | `(255, 240, 240), (255, 30, 50)` | Colors of the core and the glow. | ## Without the skill Don’t want to install the skill? Paste this prompt into Claude Code and Claude writes the script itself. ``` Add a laser beam to input.mp4. The beam is a straight line from the left edge 30% down the frame to the right edge 42% down. With d the distance in pixels from that line, draw a red (255, 30, 50) glow of strength 0.85*exp(-(d/14)^2) and, over it, a near-white (255, 240, 240) core of strength exp(-(d/2.5)^2); blend each over the frame as frame*(1-a) + color*a. Timing: every frame before 1.0 seconds is untouched. At 1.0 seconds the beam fires: its tip travels from the left edge to the right edge along the line over 0.25 seconds at constant speed, with nothing drawn past the tip (a soft 4-pixel end), and a round hot spot (Gaussian, sigma 10 pixels, same core and glow colors) rides on the tip while it moves. Once across, the beam holds, flickering by multiplying its strength by 1 - 0.08*sin(2*pi*15*t), and fades out linearly from 2.6 to 3.0 seconds; every frame from 3.0 seconds on is untouched. Use Python with numpy to draw and blend the beam and ffmpeg to read and write the video (no drawtext), keep the size, 30fps, length and audio, and save it as output.mp4. ``` ## Run it without Claude This is the exact script we tested. Save it as `laser-beam.py` and run: ``` python3 laser-beam.py input.mp4 output.mp4 ``` ``` #!/usr/bin/env python3 """Laser beam: a thin red beam with a white-hot core shoots across the frame from the left edge, holds, then fades. Usage: python3 laser-beam.py input.mp4 output.mp4 Needs ffmpeg and numpy (pip install numpy). """ import json import subprocess import sys import numpy as np FROM = (0.0, 0.30) # where the beam enters (0-1 across and down the frame) TO = (1.0, 0.42) # where it leaves START = 1.0 # second the beam fires SHOOT = 0.25 # seconds the beam's tip takes to cross the frame END = 3.0 # second it has faded out by FADE = 0.4 # seconds the fade-out takes CORE = 2.5 # half-width of the white-hot core, in pixels HALO = 14 # half-width of the red glow around it, in pixels CORE_COLOR = (255, 240, 240) # the core: near white with a touch of red HALO_COLOR = (255, 30, 50) # the glow: laser red def probe(path): info = json.loads(subprocess.check_output(["ffprobe", "-v", "error", "-select_streams", "v:0", "-show_entries", "stream=width,height,r_frame_rate", "-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) def strength(t): """0-1: how bright the beam is at time t, with a fast laser flicker.""" if t < START or t >= END: return 0.0 fade = min((END - t) / FADE, 1) return fade * (1 - 0.08 * np.sin(t * 2 * np.pi * 15)) def beam(t): """Two masks (0-1) for time t: the core and the glow, cut off past the beam's tip, plus a hot spot at the tip.""" tip = min((t - START) / SHOOT, 1) reached = np.clip((tip - along) * length / 4, 0, 1) # soft 4-pixel end at the tip core = np.exp(-(across / CORE) ** 2) * reached glow = 0.85 * np.exp(-(across / HALO) ** 2) * reached if tip < 1: # a flare rides on the tip while it travels spot = np.exp(-((along - tip) * length) ** 2 / (2 * 10 ** 2) - across ** 2 / (2 * 10 ** 2)) core, glow = np.maximum(core, spot), np.maximum(glow, np.minimum(spot * 3, 0.85)) return core[..., None], glow[..., None] src, out = sys.argv[1:3] w, h, rate, fps = probe(src) y, x = np.mgrid[0:h, 0:w].astype(np.float32) (ax, ay), (bx, by) = (FROM[0] * w, FROM[1] * h), (TO[0] * w, TO[1] * h) length = np.hypot(bx - ax, by - ay) along = ((x - ax) * (bx - ax) + (y - ay) * (by - ay)) / length ** 2 # 0 at the entry point, 1 at the exit across = np.abs((x - ax) * (by - ay) - (y - ay) * (bx - ax)) / length # pixels from the beam's center line core_rgb, halo_rgb = np.array(CORE_COLOR, np.float32), np.array(HALO_COLOR, np.float32) reader = subprocess.Popen(["ffmpeg", "-v", "error", "-i", src, "-f", "rawvideo", "-pix_fmt", "rgb24", "-"], stdout=subprocess.PIPE) writer = subprocess.Popen(["ffmpeg", "-y", "-v", "error", "-f", "rawvideo", "-pix_fmt", "rgb24", "-s", f"{w}x{h}", "-r", rate, "-i", "-", "-i", src, "-map", "0:v", "-map", "1:a?", "-c:v", "libx264", "-crf", "18", "-pix_fmt", "yuv420p", "-c:a", "copy", "-shortest", out], stdin=subprocess.PIPE) i = 0 while raw := reader.stdout.read(w * h * 3): img = np.frombuffer(raw, np.uint8).reshape(h, w, 3) t = i / fps s = strength(t) if s > 0: core, glow = beam(t) frame = img * (1 - glow * s) + halo_rgb * glow * s # red glow frame = frame * (1 - core * s) + core_rgb * core * s # white-hot core on top img = np.clip(frame, 0, 255).astype(np.uint8) writer.stdin.write(img.tobytes()) i += 1 writer.stdin.close() if reader.wait() or writer.wait(): sys.exit("ffmpeg failed") ``` ## More overlays and light - [Anamorphic streak **Anamorphic streak**](https://www.recharm.com/effects/anamorphic-streak) - [Aurora **Aurora**](https://www.recharm.com/effects/aurora) - [Blood splatter **Blood splatter**](https://www.recharm.com/effects/blood-splatter) - [Bokeh lights **Bokeh lights**](https://www.recharm.com/effects/bokeh-lights) - [Camera flash **Camera flash**](https://www.recharm.com/effects/camera-flash) ## Find 3x _winning ads_ Recharm cuts your ad footage into tagged, searchable clips: hooks, testimonials, product shots. 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