---
title: "Making Howler Emails"
date: 2025-08-09T00:00:00+00:00
draft: false
category: project
excerpt: "Harry Potter and the Chamber of Secrets has a fun form of letter called a 'howler' that shouts at the recipient. By abusing what is possible in HTML email, we can recreate this effect digitally."
---

# RONALD WEASLEY!

## What is a Howler?

In the Harry Potter universe, a Howler is a ~wave:magical letter~ that shouts its message aloud when opened.
It's typically used to deliver angry or urgent messages, often in a very dramatic fashion.
The Howler is known for its loud and booming voice, which can be quite startling for the recipient.

A prime example of a Howler can be seen in the film adaptation of "Harry Potter and the Chamber of Secrets," where Ron Weasley receives a Howler from his mother[^1] after he flies the family car (a [Ford Anglia](https://en.wikipedia.org/wiki/Ford_Anglia)) to Hogwarts.

[^1]: In the film, actress Julie Walters reportedly had to scream so loudly while recording Mrs Weasley’s Howler that she almost lost her voice by the end of the day.

<iframe width="560" height="315" src="https://www.youtube.com/embed/fBziSx7RtqY?si=6FB6ozgPAL8YzOAf" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>

## Creating a Howler Email

I extracted the audio from this clip and converted it to a more email-friendly format (OGG Vorbis) using ~the extracto charm~ [FFmpeg](https://ffmpeg.org/):

```bash
ffmpeg -i howler.mp4 -c:a libvorbis -q:a 5 howler.ogg
```

We then embed this audio file into an HTML email using the `<audio>` tag with the `autoplay` and `controls` attributes.
To ensure maximum compatibility, we base64 encode the audio file and embed it directly into the email.
To base64 encode the audio file, we can use the `base64` command-line utility.

A complete example of making an audio tag with base64 encoded audio looks like this:

```bash
cat > payload.html << EOF
'<audio autoplay controls>
  <source
    src="data:audio/ogg;base64,'$(base64 -w 0 howler.ogg)'"
    type="audio/ogg"
  />
  Your browser fortunately does not support the audio element.</audio>'
EOF
```

The resulting HTML can then be sent as an email using any email client that supports HTML emails.
Each client has different responses to incoming HTML emails, so your mileage may vary.
The most humorous response I've seen was Apple Mail automatically playing the audio _when the email arrived_, without me opening it! :blinkingguy: (Although this was circa eight years ago, so may no longer be the case.)