---
title: "How to add a glow dissolve with Claude (tested prompt and ffmpeg command)"
description: "Clip A blooms into a soft, hazy glow that never quite turns white, and clip B emerges from it as the glow fades. Install one skill and ask Claude Code, or run the ffmpeg command we tested yourself."
url: https://www.recharm.com/effects/glow-dissolve
---

# How to add a glow dissolve with Claude

Clip A blooms into a soft, hazy glow that never quite turns white, and clip B emerges from it as the glow fades.

Made by the command on this page, from our own test clips.

## 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

   ```
   Join clipA.mp4 and clipB.mp4 with a glow dissolve
   Length of the transition in seconds; the glow peaks halfway through: 1.2
   Glow radius (Gaussian blur sigma, in pixels): 28
   ```

## 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.

Put a sale badge on **@clip1.mp4**, give **@clip2.mp4** a VHS look, then join them with a glow dissolve.

## 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                                                         |
| ------- | ------- | -------------------------------------------------------------------- |
| `D`     | `1.2`   | Length of the transition in seconds; the glow peaks halfway through. |
| `BLUR`  | `28`    | Glow radius (Gaussian blur sigma, in pixels).                        |
| `GLOW`  | `1.0`   | Glow strength at the peak, from 0 (none) to 1.                       |

## Without the skill

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

```
Join clipA.mp4 and clipB.mp4 with a 1.2 second glow dissolve, starting 1.2 seconds before the end of A. Give each clip a glow: a Gaussian-blurred copy of the frame (sigma 28 pixels) laid over it in screen blend mode, done in RGB. On A the glow strength ramps from 0 to full over the first 0.6 seconds of the transition; on B it ramps from full back to 0 over the second 0.6 seconds, so the glow peaks mid-transition. Dissolve A into B with a plain 1.2 second crossfade over the same window (ffmpeg xfade fade), and crossfade the audio over the same 1.2 seconds. Match B's size and frame rate to A, output 30fps H.264 yuv420p. Use ffmpeg and save it as output.mp4.
```

## Run it without Claude

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

```
sh glow-dissolve.sh clipA.mp4 clipB.mp4 output.mp4
```

```
#!/bin/sh
# Glow dissolve: clip A blooms into a soft glow, dissolves into clip B, and the glow fades off B, over 1.2s. The sound crossfades underneath.
# Usage: sh glow-dissolve.sh clipA.mp4 clipB.mp4 output.mp4  (both clips need an audio track)
set -e
A="$1"; B="$2"; OUT="$3"
D=1.2      # transition length in seconds: the glow peaks halfway through
BLUR=28    # glow radius (gblur sigma, in pixels)
GLOW=1.0   # glow strength at the peak, 0 to 1

LEN=$(ffprobe -v error -show_entries format=duration -of csv=p=0 "$A")
OFFSET=$(echo "$LEN - $D" | bc)
HALF=$(echo "$D / 2" | bc -l)
SIZE=$(ffprobe -v error -select_streams v:0 -show_entries stream=width,height -of csv=s=x:p=0 "$A")
FPS=$(ffprobe -v error -select_streams v:0 -show_entries stream=r_frame_rate -of csv=p=0 "$A")
W=${SIZE%x*}; H=${SIZE#*x}
# The glow is a blurred copy laid over the picture in screen mode. Its strength ramps up over A's last
# half-second of the transition and back down over B's first, so the peak lands mid-dissolve.
SCREEN="(255-(255-A)*(255-B)/255)"
RISE="$GLOW*clip((T-$OFFSET)/$HALF,0,1)"
FALL="$GLOW*clip(($D-T)/$HALF,0,1)"
ffmpeg -y -i "$A" -i "$B" -filter_complex "\
[0:v]fps=$FPS,format=gbrp,setsar=1,split[a0][a1];\
[a1]gblur=sigma=$BLUR[ablur];\
[a0][ablur]blend=all_expr='A+$RISE*($SCREEN-A)',format=yuv420p[a];\
[1:v]scale=$W:$H:force_original_aspect_ratio=increase,crop=$W:$H,fps=$FPS,format=gbrp,setsar=1,split[b0][b1];\
[b1]gblur=sigma=$BLUR[bblur];\
[b0][bblur]blend=all_expr='A+$FALL*($SCREEN-A)',format=yuv420p[b];\
[a][b]xfade=transition=fade:duration=$D:offset=$OFFSET[v];\
[0:a][1:a]acrossfade=d=$D[au]" \
  -map "[v]" -map "[au]" -r 30 -c:v libx264 -crf 18 -pix_fmt yuv420p -c:a aac "$OUT"
```

## More transitions

- [Barn door transition **Barn door transition**](https://www.recharm.com/effects/barn-door)
- [Blinds transition **Blinds transition**](https://www.recharm.com/effects/blinds-transition)
- [Block dissolve **Block dissolve**](https://www.recharm.com/effects/block-dissolve)
- [Blur transition **Blur transition**](https://www.recharm.com/effects/blur-transition)
- [Bounce transition **Bounce transition**](https://www.recharm.com/effects/bounce-transition)

## 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)