CongBom

To get meta value in front-end, use <code>get_post_meta()</code> with meta key is <code>youtube_id</code>.
Example:
Print YouTube video ID: 
 ID, ‘youtube_id’, true);?>
Thumbnails: 
 <img src="http://img.youtube.com/vi/ID, ‘youtube_id’, true);?>/mqdefault.jpg” alt=”” />
Video player:
<iframe src="http://www.youtube.com/embed/ID, ‘youtube_id’, true); ?>” width=”588″ height=”331″ frameborder=”0″ allowfullscreen>

YouTube metabox

Create YouTube meta-box for post with live preview

Yoren Chang

Thanks to <a href="https://github.com/WebDevStudios/Taxonomy_Single_Term" rel="nofollow ugc">Taxonomy_Single_Term</a>, a library created by <a href="http://webdevstudios.com/" rel="nofollow ugc">WebDevStudios</a>, it made my work much easier on creating this plugin.
With Categories Metabox Enhanced, you can:
<ul>
<li>Change the built-in Categories metabox/panel to a single term UI, which means replacing the checkboxes with radio buttons or a select drop-down.</li>
<li>Apply the single term UI to other hierarchical taxonomies in the plugin’s Settings page.</li>
<li>Customized the single term UI by setting these options:
<ul>
<li>Priority and position of the metabox placement.</li>
<li>Title of the metabox.</li>
<li>If child-terms should be indenting.</li>
<li>If adding of new terms from the metabox is enable.</li>
</ul>
</li>
</ul>

Categories Metabox Enhanced

Replace the checkboxes with radio buttons or a select drop-down in the built-in Categories metabox and Gutenberg sidebar panel.

YouTube metabox vs Categories Metabox Enhanced