---
title: "How to add light trails with Claude (tested prompt and ffmpeg command)"
description: "At 1 second the shot dims and the rainbow glints on the backdrop smear into long glowing streaks that hang in the air behind the moving camera. Install one skill and ask Claude Code, or run the ffmpeg command we tested yourself."
url: https://www.recharm.com/effects/light-trails
---

# How to add light trails with Claude

At 1 second the shot dims and the rainbow glints on the backdrop smear into long glowing streaks that hang in the air behind the moving camera.

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 light trails to input.mp4
   Brightness (0-1) where a highlight starts to leave a trail: 0.86
   Brightness where the trail is at full strength: 0.90
   ```

## 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 light trails 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                                                                          |
| ------- | ------- | ------------------------------------------------------------------------------------- |
| `LOW`   | `0.86`  | Brightness (0-1) where a highlight starts to leave a trail. Lower it for more trails. |
| `HIGH`  | `0.90`  | Brightness where the trail is at full strength.                                       |
| `DECAY` | `0.975` | Share of a trail that survives each frame. Closer to 1 gives longer streaks.          |
| `GLOW`  | `2.5`   | Blur sigma in pixels that softens the streaks.                                        |
| `DIM`   | `0.75`  | The picture's brightness under the trails, so they stand out. 1 turns dimming off.    |
| `START` | `1.0`   | Second the trails start.                                                              |

## Without the skill

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

```
Add a light trails (long-exposure) effect to input.mp4 with ffmpeg, starting at 1.0 seconds; the first second stays untouched. Convert to RGB and split the video into two copies. Copy 1, the base: from 1.0 seconds on, scale every channel down to 75% of its value (output max 0.75 on a 0-1 scale). Copy 2, the trails: per channel, map input levels 0.86-0.90 to 0-1 so only the brightest highlights survive and everything darker turns black; keep it black before 1.0 seconds (fade it in over 0.04 seconds), then run ffmpeg's lagfun filter with decay 0.975 so each highlight leaves a fading trail as it moves, and soften it with a Gaussian blur of sigma 2.5 pixels. Add copy 2 onto copy 1 with an additive blend. 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 `light-trails.sh` and run:

```
sh light-trails.sh input.mp4 output.mp4
```

```
#!/bin/sh
# Light trails: from 1s the shot dims and its brightest highlights drag long glowing streaks behind them.
# Usage: sh light-trails.sh input.mp4 output.mp4
# Needs ffmpeg.
set -e
IN="$1"; OUT="$2"
LOW=0.86      # brightness (0-1) where a highlight starts to leave a trail
HIGH=0.90     # brightness where the trail is at full strength
DECAY=0.975   # share of a trail that survives each frame (closer to 1 = longer streaks)
GLOW=2.5      # blur sigma in pixels that softens the streaks
DIM=0.75      # the picture's brightness under the trails, so they stand out (1 = no dimming)
START=1.0     # second the trails start

ffmpeg -y -v error -i "$IN" -filter_complex "
  [0:v]format=gbrp,split[base][hi];
  [base]colorlevels=romax=$DIM:gomax=$DIM:bomax=$DIM:enable='gte(t,$START)'[dimmed];
  [hi]colorlevels=rimin=$LOW:gimin=$LOW:bimin=$LOW:rimax=$HIGH:gimax=$HIGH:bimax=$HIGH,
      fade=t=in:st=$START:d=0.04,lagfun=decay=$DECAY,gblur=sigma=$GLOW[trails];
  [dimmed][trails]blend=all_mode=addition,format=yuv420p[v]" \
  -map "[v]" -map 0:a? -r 30 -c:v libx264 -crf 18 -c:a copy "$OUT"
```

## More motion and camera

- [2.5D parallax photo **2.5D parallax photo**](https://www.recharm.com/effects/2-5d-parallax-photo)
- [Back-and-forth loop **Back-and-forth loop**](https://www.recharm.com/effects/back-and-forth-loop)
- [Background blur **Background blur**](https://www.recharm.com/effects/background-blur)
- [Bullet time **Bullet time**](https://www.recharm.com/effects/bullet-time)
- [Cinemagraph **Cinemagraph**](https://www.recharm.com/effects/cinemagraph)

## 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)