--- title: "How to add a slit-scan with Claude (tested prompt and script)" description: "As the camera pushes in, each lower row of the picture lags further behind in time, so the serum bottle stretches tall with a big cap over a narrow, tapering label, then eases back to normal. Install one skill and ask Claude Code, or run the Python script we tested yourself." url: https://www.recharm.com/effects/slit-scan --- # How to add a slit-scan with Claude As the camera pushes in, each lower row of the picture lags further behind in time, so the serum bottle stretches tall with a big cap over a narrow, tapering label, then eases back to normal. 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 slit-scan to input.mp4 Second the bend starts: 1.0 Second it is fully gone again: 5.5 ``` ## 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 slit-scan 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 | | ------- | ------- | -------------------------------------------------------------------------------------------------- | | `START` | `1.0` | Second the bend starts. | | `END` | `5.5` | Second it is fully gone again. | | `RAMP` | `1.0` | Seconds it takes to ease in, and to ease out. | | `DELAY` | `2.5` | Seconds the bottom row lags behind the top row at full strength. More bends moving things further. | ## Without the skill Don’t want to install the skill? Paste this prompt into Claude Code and Claude writes the script itself. ``` Add a slit-scan (time displacement) effect to input.mp4. Every output row comes from an earlier frame than the row above it: row y (0 at the top, h-1 at the bottom) of output frame i is row y of input frame i - round(L × y / (h - 1)), where L is the lag in frames, clamped so it never reaches before frame 0. L = 2.5 seconds × 30 fps × s(t), where s(t) is 0 before 1.0 seconds and after 5.5 seconds, eases up to 1 between 1.0 and 2.0 seconds and back down to 0 between 4.5 and 5.5 seconds, with the smoothstep curve u²(3 − 2u) for both ramps. So the top row is always the current frame, the bottom row is up to 2.5 seconds behind, and before 1.0 seconds and after 5.5 seconds the video is unchanged. Use Python with numpy and ffmpeg, keep the size (540x960), 30 fps and the audio, and save it as output.mp4. ``` ## Run it without Claude This is the exact script we tested. Save it as `slit-scan.py` and run: ``` python3 slit-scan.py input.mp4 output.mp4 ``` ``` #!/usr/bin/env python3 """Slit-scan: each row of the picture shows a slightly earlier moment than the row above, so anything moving bends and leans. Usage: python3 slit-scan.py input.mp4 output.mp4 Needs ffmpeg and numpy (pip install numpy). """ import json import subprocess import sys import numpy as np START = 1.0 # second the bend starts END = 5.5 # second it is fully gone again RAMP = 1.0 # seconds it takes to ease in and to ease out DELAY = 2.5 # seconds the bottom row lags behind the top row at full strength def strength(t): """0 outside START-END, easing up to 1 over RAMP seconds and back down before END.""" u = min(max(min(t - START, END - t) / RAMP, 0), 1) return u * u * (3 - 2 * u) def slit_scan(history, lag): """Build a frame row by row: row y comes from the frame lag * y / (h - 1) frames back.""" back = np.round(lag * np.arange(h) / (h - 1)).astype(int) back = np.minimum(back, len(history) - 1) frame = np.empty_like(history[-1]) for k in np.unique(back): rows = back == k frame[rows] = history[-1 - k][rows] return 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", "-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) src, out = sys.argv[1:3] w, h, rate, fps = probe(src) 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) keep = round(DELAY * fps) + 1 # frames of history the bottom row can reach back to history, i = [], 0 while raw := reader.stdout.read(w * h * 3): history = (history + [np.frombuffer(raw, np.uint8).reshape(h, w, 3)])[-keep:] lag = DELAY * fps * strength(i / fps) writer.stdin.write((slit_scan(history, lag) if lag > 0 else history[-1]).tobytes()) i += 1 writer.stdin.close() if reader.wait() or writer.wait(): sys.exit("ffmpeg failed") ``` ## More distortion and glitch - [Anaglyph 3D **Anaglyph 3D**](https://www.recharm.com/effects/anaglyph-3d) - [Black hole **Black hole**](https://www.recharm.com/effects/black-hole) - [Bulge and pinch **Bulge and pinch**](https://www.recharm.com/effects/bulge-pinch) - [Datamosh **Datamosh**](https://www.recharm.com/effects/datamosh) - [Disintegration **Disintegration**](https://www.recharm.com/effects/disintegration) ## 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)