Chris

Related YouTube Videos is a free WordPress plugin that embeds a number of, well, YouTube videos that are related to your content. The list is put together by using the YouTube search API. And you can specify the relation between the videos and your content by:
<ul>
<li>the title of your current post, page or custom post type.</li>
<li>the tags of your current post, page or custom post type.</li>
<li>the categories of your current post, page or custom post type.</li>
<li>any keywords you specify.</li>
</ul>
Also, this plugin offers you two ways to embed related videos:
<ol>
<li>by using the shortcode [relatedYouTubeVideos] somewhere in your post/page content.</li>
<li>by using the WordPress widget “Related YouTube Videos” in any of your widget areas (multiple instances are possible).</li>
</ol>
<h4>Disclaimer / Important</h4>
As of April 2015 the YouTube API can only be accessed when you have a valid key for the data API. Also, the number of free requests per day is limited!
There is a nice and short video tutorial (https://www.youtube.com/watch?v=zOYW7FO9rzA) on how to get such an API key. But it’s up to you to make sure your stay within the free limit or keep track of the costs when you need more than that!
Please read Youtube and Google’s terms and conditions for more details.
<h4>The Shortcode</h4>
I’m only going to explain the options/paramters for the shortcode but they work exactly the same for the widget, of course.
You can put the shortcode [relatedYouTubeVideos] anywhere you want inside the content of a page, post, or custom post type – as long as your WordPress theme is supporting shortcodes.
You can use the following options/parameters/attributes:
Appearance
<ul>
<li>id – You can specify the HTML id attribute for the wrapping <code><ul></code> element.</li>
<li>class – You can specify an additional HTML class name for the wrapping <code><ul></code> element</li>
<li>width – Width of the HTML video object</li>
<li>height – Height of the HTML video object</li>
<li>preview – “true” will only display the preview image and only load the video (via Javascript!) when this image has been clicked.</li>
<li>showVideoTitle – “true” if you want to show the video title right below the video itself. Can be styled via CSS class <code>.title</code></li>
<li>showVideoDescription – “true” if you want to show the video description below the video, respectively, when the video title is displayed right below the title. Can be styled via CSS class <code>.description</code> </li>
<li>autoplay – “true” if you want the video to automatically start playing when ready. This will obviously not work in preview mode!!</li>
<li>exclude – Comma separated list of post/page IDs where no videos shall be displayed.</li>
</ul>
Configuration
<ul>
<li>max – Number of videos (or search results) that will be returned. Can be any number between 1 and 10!</li>
<li>random – Select MAX number of videos out of RANDOM number of videos.</li>
<li>offset – START and OFFSET are interchangably the same and just other words for the same option.</li>
</ul>
YouTube
<ul>
<li>relation – Specify the kind of relation that shall be used for searching YouTube. Can either be ‘postTitle’, ‘postTags’, ‘postCategories’, or ‘keywords’ (in which case the attribute ‘terms’ will be used for the YouTube search).</li>
<li>terms – Search YouTube for these terms – no separating commas required.</li>
<li>exact – Set to ‘true’ will (try to) search for the exact phrase.</li>
<li>orderBy – Can either be ‘published’, ‘rating’, ‘viewCount’, (default) ‘relevance’.</li>
<li>lang – {2-letter-language-code} will show videos in that language.</li>
<li>region – {2-letter-country-code} will show videos that are actually viewable in that region/country.</li>
<li>author – Only show videos from a given YouTube User(name) .</li>
<li>filter – Add additional keywords or filtering search parameters. Those will always be added even when the relation is set to post title, tags, or so. You can also manually add post tags by adding ‘+postTags’, categories by adding ‘+postCategories’, the post title by adding ‘+postTitle’, post meta data by adding ‘+postMeta:key’ to the filter.</li>
<li>viewRelated – set to “no” or “false” will not show more related videos at the end of a clip.</li>
</ul>
I recommend always using the attributes ‘relation’, ‘max’, and if the relation shall be ‘keywords’ the ‘terms’ attribute. Depending on your design you might also set a custom width and height for the videos so they fit in properly.
Shortcode Example 1: [relatedYouTubeVideos relation=”postTags” max=”3″] Will show three videos coming back from the search YouTube for (all!) the tags you have assigned to this post or page.
Shortcode Example 2: [relatedYouTubeVideos relation=”keywords” terms=”monty python” max=”5″] Will show five Monty Python videos from YouTube.
Shortcode Example 3: [relatedYouTubeVideos relation=”keywords” terms=”real madrid” exact=”true” max=”2″] Will search for the exact phrase “Real Madrid” and (hopefully) not just anything “real”.
Shortcode Example 4: [relatedYouTubeVideos relation=”postTitle” max=”1″ orderBy=”viewCount” start=”1″] Will show the second most popular video (the first being skipped) relating to your post or page title.
Shortcode Example 5: [relatedYouTubeVideos relation=”keywords” terms=”monthy python” max=”1″ showVideoTitle=”true” showVideoDescription=”true”] Will show a Monty Python video, followed by the video title, followed by the video, followed by the video description.
Shortcode Example 6: [relatedYouTubeVideos relation=”keywords” terms=”monthy python” max=”1″ preview=”true”] Will show the thumbnail of a Monty Python video and load + play the video only when it’s being clicked.
Shortcode Example 7: [relatedYouTubeVideos relation=”postTitle” filter=”intitle:official -intitle:cover” max=”1″ preview=”true”] If the post title is about a music video (band and song title, for example) this will only show the official music video.
Shortcode Example 8: [relatedYouTubeVideos relation=”postTitle” filter=”+postCategories” max=”1″ preview=”true”] Will use the post title and a list of all categories the post is in to search YT.
<h4>The Widget</h4>
The widget almost works the same way. Or at least it has the same options for configuring the video request. If you log into your WordPress backend and go to the “Appearance > Widget” menu (given that your theme supports widgets) you can drag&drop a widget instance into the widget area of your choice.
The relatedYouTubeVideos widget allows multiple instances. So you can put as many widgets as you like into as many widget areas as you like.
The difference between the widget and the shortcode is not in terms of functionality but usually in the context they reside. Widgets usually go into sidebars or footers and alike and the same widget usually shows up for many, if not all pages, just the same. Shortcodes are placed inside the actual content and therefore will only show up when the page or post where they’re put is shown.
There is one functionality that only applies to widgets: In the options field “Hide on” you can set a list of comma separated, numerical post IDs on which the widget will not show up. This way you can easily exlude the widget on certain post. You can also use PAGE ids for that matter, since under the hood WordPress manages all “post type” IDs the same.
<h4>Randomize Results</h4>
The same keywords (or post title/tags) will ususally return the same video(s) for a period of time. Basically, that’s up to YouTube but in can take days, weeks or even months until fresh videos will show up.
When you set a numeric value for the RANDOM parameter/option you can get random videos from a pool of results. The MAX value plays along with the RANDOM value and both read like this: Show me {MAX} random videos out of {RANDOM} videos.
[relatedYouTubeVideos relation=”keywords” terms=”fast cars” max=”2″ random=”10″] will actually request 10 videos from YouTube but only show 2 random ones out of that 10.
So RANDOM will determine the size of the pool MAX videos will be chosen from.
<h4>System Requirements</h4>
In order to run this plugin you need the following components installed and enabled in your server and PHP environment:
<ul>
<li>PHP 5.1.2+</li>
<li>SimpleXML (usually is enabled by default anyways)</li>
<li>cURL (preferred) or fopen/fsockopen</li>
<li>OpenSSL + HTTPS wrapper (is only required if cURL is not available)</li>
<li>WordPress 3.0+</li>
</ul>
In general you should not have to worry about these things since they’re included in most web hosting packages nowadays. 
But to be sure you can download and install this plugin and then check the backend page. There is a “System Requirements” section that will show you exactly if you can good to go or if there is any problem.
In case you’re getting a “URL file-access is disabled in the server configuration” error you should make sure your PHP.ini file contains these two lines:
allow_url_include = on
allow_url_fopen = on
<h4>Available Languages:</h4>
<ul>
<li>English</li>
<li>German</li>
<li>
Serbo-Croatian – by Borisa Djuraskovic (<a href="http://www.webhostinghub.com/" rel="nofollow ugc">Webhostinghub</a>) 
Developers can also use the API class outside the plugin context, for example in a theme template file. All you have to do is include the class (if it doesn’t already exist) and create an object like this:
/* Load the “Related YouTube Videos” API class if it does not exist yet. */ 
if( !class_exists( ‘RelatedYouTubeVideos_API’ ) ) {
$file = str_replace( ‘/’, DIRECTORY_SEPARATOR, ABSPATH ) . ‘lib’ . DIRECTORY_SEPARATOR . ‘RelatedYouTubeVidoes’ . DIRECTORY_SEPARATOR . ‘API.php’;
if( file_exists( $file ) ) {
<pre><code>include_once $file;
</code></pre>
}
} 
/* Only continue if the API class could be loaded properly. */ 
if( class_exists( ‘RelatedYouTubeVideos_API’ ) ) {
$RytvAPI = new RelatedYouTubeVideos_API();
/* Do your configuration */ 
 $data = $RytvAPI->validateConfiguration( 
 array( 
 ‘relation’ => ‘postTitle’, 
 ‘max’ => ‘3’, 
 ‘width’ => 150, 
 ‘height’ => 150, 
 ‘lang’ => ‘en’, 
 ‘region’ => ‘de’, 
 ‘class’ => ‘left center inline bg-black’, 
 ‘preview’ => true 
 ) 
 );
/* Search YouTube. */ 
 $results = $RytvAPI->searchYouTube( $data );
/* Generate the unordered HTML list of videos according to the YouTube results and your configuration. */ 
 $html = $RytvAPI->displayResults( $results, $data );
echo $html; // Or do with it whatever you like 😉
}
</li>
</ul>

alphasis

This Plugin will display the related posts list via categories. 
It can automatically display the related posts list after the content of any single post of selected post types by options. 
There are many options for the display, order, exclusion and post-type selection. 
This plugin works when viewing a post of selected post types by options. 
This plugin requires jQuery 1.6 or higher.
<h4>Official Page</h4>
<ul>
<li>Plugin’s Official Page : <a href="http://alphasis.info/developments/wordpress-plugins/related-posts-via-categories/" title="Plugin's Official Page in English" rel="nofollow ugc">English</a> / <a href="http://alphasis.info/kaihatu/wordpress-plugins/related-posts-via-categories/" title="Plugin's Official Page in Japanese" rel="nofollow ugc">Japanese</a></li>
<li>Author’s Website : <a href="http://alphasis.info/" title="alphasis.info" rel="nofollow ugc">alphasis.info</a> (Japanese) » <a href="http://alphasis.info/developments/wordpress-plugins/" title="WordPress Plugins" rel="nofollow ugc">WordPress Plugins</a> (English)</li>
</ul>
<h4>Related Posts via Categories – Options</h4>
‘Settings’ » ‘Related Posts via Categories’
<h4>Display</h4>
<ul>
<li>Auto display
<ul>
<li>This option automatically displays related posts after the content on the single post page.</li>
<li>If this option is off, you will need to manually insert <code>display_related_posts_via_categories()</code> into your theme files.</li>
</ul>
</li>
<li>Maximum number of related posts
<ul>
<li>If you do not enter anything: 10</li>
</ul>
</li>
<li>Related posts title
<ul>
<li>For example: Related Posts</li>
</ul>
</li>
<li>Before related posts title and related posts
<ul>
<li>For example: <code><div id="related-posts-via-categories"></code></li>
</ul>
</li>
<li>After related posts title and related posts
<ul>
<li>For example: <code></div></code></li>
</ul>
</li>
<li>Before related posts title
<ul>
<li>For example: <code><h2 id="related-posts-via-categories-title"></code></li>
</ul>
</li>
<li>After related posts title
<ul>
<li>For example: <code></h2></code></li>
</ul>
</li>
<li>Before related posts
<ul>
<li>For example: <code><ul id="related-posts-via-categories-list"></code></li>
</ul>
</li>
<li>After related posts
<ul>
<li>For example: <code></ul></code></li>
</ul>
</li>
<li>Before each related post
<ul>
<li>For example: <code><li class="related-posts-via-categories-item"></code></li>
</ul>
</li>
<li>After each related post
<ul>
<li>For example: <code></li></code></li>
</ul>
</li>
</ul>
<h4>Order</h4>
<ul>
<li>Order By
<ul>
<li>Related Scores : High ( Speedy ) </li>
<li>Related Scores : High / Date Published : New ( Default setting )</li>
<li>Related Scores : High / Date Published : Old</li>
<li>Related Scores : Low / Date Published : New</li>
<li>Related Scores : Low / Date Published : Old</li>
<li>Related Scores : High / Date Modified : New</li>
<li>Related Scores : High / Date Modified : Old</li>
<li>Related Scores : Low / Date Modified : New</li>
<li>Related Scores : Low / Date Modified : Old</li>
<li>Date Published : New</li>
<li>Date Published : Old</li>
<li>Date Modified : New</li>
<li>Date Modified : Old</li>
</ul>
</li>
</ul>
<h4>Exclude</h4>
<ul>
<li>Exclude (Posts)
<ul>
<li>The IDs of any posts you want to exclude, separated by commas.</li>
</ul>
</li>
<li>Exclude (Categories)
<ul>
<li>Select checkboxes of any categories you want to exclude.</li>
</ul>
</li>
</ul>
<h4>Post types</h4>
<ul>
<li>Select checkboxes of any post types you want to include in the list of Related Posts and display the list.</li>
<li>Displays checkboxes of them when there is any custom post types.</li>
</ul>
<h4>Localization</h4>
<ul>
<li>Japanese (ja) – <a href="http://alphasis.info/" title="alphasis.info" rel="nofollow ugc">alphasis</a> (plugin author)</li>
<li>Persian (fa_IR) – <a href="http://qanal.ir/" title="Omid Sheerkavand" rel="nofollow ugc">Omid Sheerkavand</a></li>
<li>Armenian (hy_AM) – <a href="http://ablog.gratun.am" title="Artak Kolyan" rel="nofollow ugc">Artak Kolyan</a></li>
<li>Current release supports English, Persian, Armenian and Japanese.</li>
</ul>

Related YouTube Videos vs Related Posts via Categories