WordPress version 3.5 removed few settings like using custom uploads folder and configuring auto-embeds (oEmbed) options. Now from WordPress 3.5 onwards, the auto-embed feature is automatically enabled by default. This means, if you paste URL of any Tweet, Youtube video, Flickr image – it will show actual embeded content in your WordPress post as against simple text based URL.
Disable auto-embeds (oEmbed) setting in WordPress
Previously, we could easily disable and stop auto emebdedding of media content from Youtube, Twitter, Flickr and so on by going to Media Settings. However, this option has been removed in new version of WordPress.
To successfully disable auto-emebds in new WordPress, you can use plugin Auto-embeds Disabler. Just copy the code and save auto-embeds-disabler.php file. Then copy this file to your plugins folder [wp-content/plugins], activate the plugin and auto-embeds feature should stop working.
Customize & change auto-embed width in WordPress
If you like to keep auto-embed feature enabled (like majority of WordPress users), then you can customize its display according to your theme layout. Previously, we had settings to enter custom width and height for auto emebds. Since that option is removed now, you can configure the same using manual code method. Just add following code to functions.php file
if ( ! isset( $content_width ) ) $content_width = 450;
Above 450 is maximum width for auto emebd media that is displayed in content section of your WordPress blog. You can increase or decrease it depending on the default width of content area on your blog. [via WP Beginner]