Although easy media embeds (i.e. YouTube, Flickr, Vimeo, etc) has been available in WordPress since version 2.9, the June 2012 update to 3.4 focused a light on that capability by adding support for easily including Tweets in posts.
So (for instance) if you want to embed a YouTube video or a Tweet in your post, all you need to do is enter the specific URL for the item. This is much easier for most users than digging around in the HTML and pasting code. Also very helpful for folks emailing posts.
- Go to Settings: Media – and make sure the “AUTO EMBED” option is checked (see image).
- Then when writing your post, simply paste your URL into your content area. Make sure that the URL is on its own line and not hyperlinked (clickable when viewing the post).
- The most popular support sites include YouTube, Vimeo, Flickr, Scribd, Twitter, and Hulu.
Full details – including the list of supported sites – at: http://codex.wordpress.org/Embeds.