WordPress plugin to fix oEmbed over HTTPS for services not embedding the correct schema (e.g. YouTube).

secure-oembed.php

<?php
/* 
Plugin Name: Secure oEmbed
Plugin URI: https://gist.github.com/goblindegook/9057159
Description: Ensure oEmbed over HTTPS.
Version: 1.0
Author: Luís Rodrigues
License: GPL 3.0
*/

/**
 * Replace http:// with https:// in the embed code (before caching).
 * 
 * @param string $data The returned oEmbed HTML.
 * @param string $url  URL of the content to be embedded.
 * @param array  $args Optional arguments, usually passed from a shortcode.
 */
function secure_oembed_result ($data, $url, $args)
{
    return preg_replace( '/http:\/\//', 'https://', $data );
}

/**
 * Replace http:// with https:// in the embed code (after caching).
 * 
 * @param mixed  $cache   The cached HTML result, stored in post meta.
 * @param string $url     The attempted embed URL.
 * @param array  $attr    An array of shortcode attributes.
 * @param int    $post_ID Post ID.
 */
function secure_embed_oembed_html ($cache, $url, $attr, $post_ID)
{
    return preg_replace( '/http:\/\//', 'https://', $cache );
}

if (is_ssl()) {
    add_filter( 'oembed_result'     , 'secure_oembed_result'    , 10, 3 );
    add_filter( 'embed_oembed_html' , 'secure_embed_oembed_html', 10, 4 );
}