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It’s the same oEmbed functionality you know and love from your WP 2.9 post editor, now enabled for comments!
Your comments can now embed content from the following sites:
<ul>
<li>YouTube</li>
<li>Blip.tv</li>
<li>Vimeo</li>
<li>DailyMotion</li>
<li>Flickr</li>
<li>Hulu</li>
<li>Viddler</li>
<li>Qik</li>
<li>Revision3</li>
<li>Photobucket</li>
<li>Scribd</li>
<li>WordPress.tv</li>
</ul>
How do you use the plugin? Simple! Input any URL from one of the listed sites above into a comment.
When the comment is posted and approved, the URL automagically transforms into the embedded content.
<h3>Blacklist feature</h3>
This feature allows you to blacklist websites from being processed by oEmbed.
For example, say I wanted to block YouTube links from being embedded.
Open <code>oembed-config.php</code> in a text editor and add the following line to the end:
<pre><code>$oembed_comments['blacklist'][] = 'youtube.com';
</code></pre>
This will blacklist all links from YouTube.com from being parsed.
<h3>Known issues</h3>
<ul>
<li>Hyperlinking an oEmbeddable link and inputting the same link in plain text will show the oEmbeddable item three times (two times if using anchor text) (not many people will do this)</li>
</ul>
<h3>Special thanks</h3>
<ul>
<li><a href="http://www.viper007bond.com/" rel="nofollow ugc">Viper007Bond</a> – for creating the WP_oEmbed class</li>
<li><a href="https://buddypress.org/developers/apeatling/" rel="nofollow ugc">apeatling</a> – for performance enhancements</li>
</ul>
<h3>Donate!</h3>
There are a couple of ways you can choose to support me:
<ul>
<li><a href="https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=V864MRMV6DTKN" rel="nofollow ugc">Fund my work soundtrack!</a> Music helps me help you! A dollar lets me buy a new tune off Amazon MP3, Amie Street or emusic.com! Or if you’re feeling generous, you can help me buy a whole CD! If you choose to donate, let me know what songs or which CD you want me to listen to! 🙂</li>
<li>Rate this plugin</li>
</ul>

oEmbed for Comments

Enable oEmbed support for comments.  Requires WP 2.9+.

Embedly

Enhance the default WordPress embedding to get previews for any article, 
including your own blog posts. You also get embeds for Gfycat, Twitch, Google 
Maps, and Embedly’s growing list of <a href="http://embed.ly/providers" rel="nofollow ugc">500+ supported 
providers</a>.
You can customize the style of the embeds, to optimize for darker WP themes, 
alignment, and width. In addition, social buttons can be added around the embeds 
to make it easier to share content from your blog posts.
If you have an Embedly Cards account, you can link it to the plugin with your Embedly API key. Not only does this remove branding from the cards, it also gives you access to analytics and viewer behaviors for most popular music and video player embeds (YouTube, Vimeo, Instagram, SoundCloud). Find out how many people viewed your embeds for how long. To learn more about Embedly Cards please visit <a href="http://embed.ly/cards" rel="nofollow ugc">our website</a>.
Using it is as simple as the default WordPress embedding. Embed media by pasting its URL in a single line when writing a post
The plugin automatically displays an embed of the media in the WordPress post 
editor (for WP 4.0+).
Fair Warning: This plugin generates static HTML content for your posts. After you deactivate 
the plugin, that HTML will still remain behind in all posts where the plugin was used to create 
embeds.

The Embedly Plugin extends Wordpress's auto-embed feature to give your blog more media types and style optons.

oEmbed for Comments vs Embedly