The Fediverse Autoembedding Mystery Untangled

Testing some fediversal URL auto embeds for WordPress happening in this here blog, now with slapping a naked URL on its own line:

https://cosocial.ca/@cogdog/115613213272065972

which embeds beautifully just like this- SHAZAM!~

Alan is @cogdog

@cogdog@cosocial.ca

For the Love of Carnegie Libraries https://carnegielibraries.org/

November 26, 2025, 12:40 am 0 boosts 0 favorites

Can we go beyond mastodon? What about a pixelfed URL?

https://pixelfed.social/p/cogdog/873949556324687103

and yup. I am seeing an embedded pixelfed photo here. WINNING!

CogDog FediPix

@cogdog@pixelfed.social

Harvesting Sun

September 17, 2025, 3:23 pm

As it turns out I have been wrong about how this is working. I had been using some code I have stuffed in a Cogdog Auto Embed Extras WordPress Plugin I have for a variety of extra auto embeds, used elsewhere in SPLOTbox theme. Typically these are set up because the URL patterns are pretty easy to match, but with fedistuff, the domains are not known in advance,

The relevant code for Mastodon and Pixelfeed is a regex search that looks for URLs like:

https://any.instance.blah/@[username_string]/string_of_digits0-9/

It seems to match all fediverse URLs, I guess it could barf on something else. For the maybe one reader who might follow along,these are set up be registering the embed patterns.

add_action( 'init', 'cdb_register_embeds' );

function cdb_register_embeds() {
	// handler for mastodon		
	wp_embed_register_handler(
		'mastodon',
		'#^https?:\/\/((?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9])\/@([a-zA-Z0-9\_]+)\/(\d+)$#i',
		'cdb_handler_mastodon'
	);
	
	
	// handler for pixelfed
	wp_embed_register_handler(
		'pixelfed',
		'#^https?:\/\/((?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9])\/p\/[a-zA-Z0-9\_]+\/(\d+)$#i',
		'cdb_handler_pixelfed'
	);

}

And these each reference a function called to embed them as iframes:

function cdb_handler_mastodon( $matches, $attr, $url, $rawattr ) {
	// handler for mastodon embeds
	$embed = '<iframe src="https://' . esc_attr($matches[1]) . '/@' . esc_attr($matches[2]) . '/' . esc_attr($matches[3]) . '/embed" class="mastodon-embed" style="max-width: 100%; border: 0" width="800" allowfullscreen="allowfullscreen"></iframe><script src="https://' . esc_attr($matches[1]) . '/embed.js" async="async"></script>';

	return $embed;
}

function cdb_handler_pixelfed( $matches, $attr, $url, $rawattr ) {
	// handler for pixelfed embeds
	$embed = '<iframe src="' . esc_attr($matches[0]) .  '/embed?caption=false&likes=false&layout=compact" class="pixelfed__embed" style="max-width:100%; min-height:600px; border:0" width="600" allowfullscreen="allowfullscreen"></iframe><script async defer src="https:/' . esc_attr($matches[1]) . '/embed.js" async="async"></script>';

	return $embed;
}

But then, while testing the ActivityPub setup I had toyed with on WordPress.com when it first came out. In writing that post, I could see WordPress was autoembedding a Mastodon URL — how was it doing that?

This is on?

First I commented out my crufty duct tape code above, and redid the two embeds at the top of the post- the pixelfed one is much better than what I had before.

So I started testing on a few other websites and discovered:

• I do not get fediverse autoembeds on many sites (It renders the naked URL)
• It does work only on sites with the ActivtyPub plugin enabled, I get a embed,

What to do? I download the ActivityPub plugin, poke around the include directory, and find a file class-embed.php which indicates at the top:

<?php
/**
 * ActivityPub Embed Handler.
 *
 * @package Activitypub
 */

namespace Activitypub;

/**
 * Class to handle embedding ActivityPub content.
 */
class Embed {

:
:

I am not sure I understand everything, but I am sure that enabling the ActivtyPub plugin on a WordPress sites gives as a bonus the autoembeds of fediverse URLs. I can’t find this mentioned anywhere I have looked so far.

With this I live up to the spirit of my pinned Mastodon post, which I can embed with just pasting its URL in here every so seriously:

Alan is @cogdog

@cogdog@cosocial.ca

@tdc #dailycreate #tdc4330 #ds106 Voltaire had an unsaid but well known life summary. I take mine seriously, inevitable SERIOUSNESS .

January 23, 2024, 9:36 pm 1 boosts 10 favorites

Expect a lot more of these!

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Featured Image: 2013/365/52 The Potter Box flickr photo by cogdogblog shared under a Creative Commons (BY 2.0) license A mystery box of electronics sent to me by Grant Potter — hey man, it still works!