---
title: "How to add a blur region with Claude (tested prompt and ffmpeg command)"
description: "At one second a box over the bottle's label turns into a heavy frosted blur that hides the text, while the backdrop, cap and stand stay sharp. Install one skill and ask Claude Code, or run the ffmpeg command we tested yourself."
url: https://www.recharm.com/effects/blur-region
---

# How to add a blur region with Claude

At one second a box over the bottle's label turns into a heavy frosted blur that hides the text, while the backdrop, cap and stand stay sharp.

Made by the command 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 blur region to input.mp4
   Top-left corner of the box, as shares of the frame width and height: 0.28, 0.48
   Box width and height as shares of the frame: 0.44, 0.26
   ```

## 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 blur region 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 command.

| Setting | Default      | What it does                                                         |
| ------- | ------------ | -------------------------------------------------------------------- |
| `X, Y`  | `0.28, 0.48` | Top-left corner of the box, as shares of the frame width and height. |
| `W, H`  | `0.44, 0.26` | Box width and height as shares of the frame.                         |
| `BLUR`  | `24`         | Blur radius in pixels. Higher hides more.                            |
| `START` | `1.0`        | Second the blur switches on. It stays to the end.                    |

## Without the skill

Don’t want to install the skill? Paste this prompt into Claude Code and Claude writes the command itself.

```
In input.mp4, blur one rectangle of the frame with ffmpeg. The box starts 28% across and 48% down from the top-left corner and is 44% of the frame wide and 26% of the frame tall (on a 540x960 frame: x 151 to 389, y 461 to 710), which covers the bottle's label. Before 1.0 seconds leave the video untouched; from 1.0 seconds to the end, replace that box with a heavily blurred copy of itself (boxblur with radius 24 and 3 passes) and leave everything outside the box exactly as it was. Keep the size, 30fps and the audio. There's no text to draw, but if you add any, draw it with Pillow, not ffmpeg's drawtext. Save it as output.mp4.
```

## Run it without Claude

This is the exact command we tested. Save it as `blur-region.sh` and run:

```
sh blur-region.sh input.mp4 output.mp4
```

```
#!/bin/sh
# Blur region: from 1s, a box over the bottle's label turns to a heavy blur while the rest stays sharp.
# Usage: sh blur-region.sh input.mp4 output.mp4
# Needs ffmpeg.
set -e
IN="$1"; OUT="$2"
X=0.28; Y=0.48     # top-left corner of the box (0-1 across and down the frame)
W=0.44; H=0.26     # box width and height as shares of the frame
BLUR=24            # blur radius in pixels (higher hides more)
START=1.0          # second the blur switches on; it stays to the end

ffmpeg -y -i "$IN" -filter_complex "[0:v]split[base][copy];\
[copy]crop=iw*$W:ih*$H:iw*$X:ih*$Y,boxblur=$BLUR:3[blurred];\
[base][blurred]overlay=W*$X:H*$Y:enable='gte(t,$START)',fps=30,format=yuv420p[v]" \
  -map "[v]" -map 0:a? -c:v libx264 -crf 18 -c:a copy "$OUT"
```

## More layouts and reframing

- [Background replacement **Background replacement**](https://www.recharm.com/effects/background-replacement)
- [Binocular view **Binocular view**](https://www.recharm.com/effects/binocular-view)
- [Cinematic bars **Cinematic bars**](https://www.recharm.com/effects/cinematic-bars)
- [Comic panel layout **Comic panel layout**](https://www.recharm.com/effects/comic-panel-layout)
- [Corner pin **Corner pin**](https://www.recharm.com/effects/corner-pin)

## 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)