RONALD WEASLEY!

What is a Howler?

In the Harry Potter universe, a Howler is a 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 mother¹ after he flies the family car (a Ford Anglia) to Hogwarts.

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:

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:

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! (Although this was circa eight years ago, so may no longer be the case.)