---
title: "How to add a glow with Claude (tested prompt and ffmpeg command)"
description: "From half a second in, the shimmering backdrop and the highlights on the acrylic block flare into soft white halos that spill light over the darker dropper and bottle. Install one skill and ask Claude Code, or run the ffmpeg command we tested yourself."
url: https://www.recharm.com/effects/glow-bloom
---

# How to add a glow with Claude

From half a second in, the shimmering backdrop and the highlights on the acrylic block flare into soft white halos that spill light over the darker dropper and bottle.

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 glow to input.mp4
   Only brightness above this (0-1) glows: 0.78
   Blur sigma in pixels: how far the light spreads: 16
   ```

## 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 glow 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                                                    |
| ----------- | ------- | --------------------------------------------------------------- |
| `THRESHOLD` | `0.78`  | Only brightness above this (0-1) glows. Lower it for more glow. |
| `RADIUS`    | `16`    | Blur sigma in pixels: how far the light spreads.                |
| `STRENGTH`  | `0.7`   | How much of the halo is added back onto the picture (0-1).      |
| `START`     | `0.5`   | Second the glow starts fading up.                               |
| `RAMP`      | `1.0`   | Seconds it takes to reach full strength. 0 turns it on at once. |

## Without the skill

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

```
Add a glow (bloom) effect to input.mp4 with ffmpeg: convert to RGB, take a copy that keeps only brightness above 0.78 on a 0-1 scale (map 0.78-1.0 to 0-1, everything darker goes black), blur it with a Gaussian blur of sigma 16 pixels, and add it back onto the original frame (additive blend) at 70% strength. The glow is off for the first 0.5 seconds, then fades up linearly to full strength over 1 second and stays on to the end. Keep the size, the 30fps frame rate, the 6-second length and the audio, encode H.264 yuv420p, and save it as output.mp4.
```

## Run it without Claude

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

```
sh glow-bloom.sh input.mp4 output.mp4
```

```
#!/bin/sh
# Glow: the brightest parts of the picture spill a soft halo of light around them, fading up from 0.5s.
# Usage: sh glow-bloom.sh input.mp4 output.mp4
# Needs ffmpeg.
set -e
IN="$1"; OUT="$2"
THRESHOLD=0.78   # only brightness above this (0-1) glows
RADIUS=16        # blur sigma in pixels: how far the light spreads
STRENGTH=0.7     # how much of the halo is added back onto the picture (0-1)
START=0.5        # second the glow starts fading up
RAMP=1.0         # seconds it takes to reach full strength

ffmpeg -y -v error -i "$IN" -filter_complex "
  [0:v]format=gbrp,split[base][hi];
  [hi]colorlevels=rimin=$THRESHOLD:gimin=$THRESHOLD:bimin=$THRESHOLD,gblur=sigma=$RADIUS,fade=t=in:st=$START:d=$RAMP[glow];
  [base][glow]blend=all_mode=addition:all_opacity=$STRENGTH,format=yuv420p[v]" \
  -map "[v]" -map 0:a? -r 30 -c:v libx264 -crf 18 -c:a copy "$OUT"
```

## 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. 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)