---
title: "How to add a strobe with Claude (tested prompt and ffmpeg command)"
description: "From 1 to 3 seconds the shot blinks between a brightened picture and solid black every two frames, like it's lit by a strobe light. Install one skill and ask Claude Code, or run the ffmpeg command we tested yourself."
url: https://www.recharm.com/effects/strobe
---

# How to add a strobe with Claude

From 1 to 3 seconds the shot blinks between a brightened picture and solid black every two frames, like it's lit by a strobe light.

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 strobe to input.mp4
   Second the strobe starts: 1.0
   Seconds it runs: 2.0
   ```

## 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 strobe 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                                                                                               |
| ------- | ------- | ---------------------------------------------------------------------------------------------------------- |
| `AT`    | `1.0`   | Second the strobe starts.                                                                                  |
| `DUR`   | `2.0`   | Seconds it runs.                                                                                           |
| `ON`    | `2`     | Frames each flash and each black gap lasts. 2 at 30fps is 7.5 flashes a second; 1 is the fastest possible. |
| `BOOST` | `0.12`  | How much brighter the flashes are than the normal picture. 0 leaves them unchanged.                        |

## 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, add a strobe from 1.0 to 3.0 seconds. Work at 30fps and count frames from 1.0s (frame 30 of the video is strobe frame 0). Split the strobe into runs of 2 frames: runs 0, 2, 4... (strobe frames 0-1, 4-5, 8-9 and so on) are flashes, where the picture is brightened with ffmpeg's eq filter at brightness=0.12 and contrast=1.2; runs 1, 3, 5... (strobe frames 2-3, 6-7 and so on) are solid black (0, 0, 0) over the whole frame. That gives 7.5 flashes a second for 60 frames, ending on black at frame 89. Before 1.0s and from 3.0s on, the video must be unchanged. Keep the size, 30fps, 6 second length and audio the same. Use ffmpeg and save it as output.mp4 (H.264, yuv420p).
```

## Run it without Claude

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

```
sh strobe.sh input.mp4 output.mp4
```

```
#!/bin/sh
# Strobe: for two seconds the picture flashes on, brighter than normal, and cuts to black, a few times a second.
# Usage: sh strobe.sh input.mp4 output.mp4
set -e
IN="$1"; OUT="$2"
AT=1.0     # second the strobe starts
DUR=2.0    # seconds it runs
ON=2       # frames each flash and each black gap lasts (2 at 30fps = 7.5 flashes a second)
BOOST=0.12 # how much brighter the flashes are than the normal picture (0 = unchanged)

END=$(echo "$AT + $DUR" | bc)
# while the strobe is live (AT up to END), frames since AT go in runs of ON: even runs are a
# brightened flash, odd runs are covered in black
RUN="floor(((t-$AT)*30+0.5)/$ON)"
LIVE="gte(t,$AT)*lt(t,$END-0.01)"
ffmpeg -y -i "$IN" -vf "fps=30,\
eq=brightness=$BOOST:contrast=1.2:enable='$LIVE',\
drawbox=x=0:y=0:w=iw:h=ih:c=black:t=fill:enable='$LIVE*mod($RUN,2)'" \
  -c:v libx264 -crf 18 -pix_fmt yuv420p -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)