init.php

<?php
class YoutubeFrames extends Plugin {

	private $host;

	function about() {
		return array(1.0,
		"Embed Youtube videos using iframes",
		"dugite-code");
	}

	function init($host) {
		$this->host = $host;

		$host->add_hook($host::HOOK_ARTICLE_FILTER, $this);
		$host->add_hook($host::HOOK_IFRAME_WHITELISTED, $this);
	}

	function hook_iframe_whitelisted($src) {
		return in_array($src, ["www.youtube.com", "youtube.com", "youtu.be", "youtube-nocookie.com", "www.youtube-nocookie.com"]);
	}

	function hook_article_filter($article) {

		// Basic link matching
		if ( strpos($article["link"], "youtube.com") !==false ){
			$domDocument = new DOMDocument();
			$domElement = $domDocument->createElement("iframe","");
			$newnode = $domDocument->appendChild($domElement);

			// Get video ID from link
			$urlparts = explode("v=", $article["link"]);
			$embed_link = "https://www.youtube-nocookie.com/embed/".$urlparts[1];

			// Add src attribute
			$newnode->setAttribute("src", $embed_link);
			$newnode->setAttribute("frameborder", "0");
			// Save domDocument as html and replace article content
			$article["content"] = $domDocument->saveHTML();


		}

		// Return article
		return $article;
	}

	function api_version() {
		return 2;
	}

}