To embed a YouTube video in a post, simply copy the URL of the video, or get the embed URL from YouTube, and place it in an embed code like this:
[youtube url="http://www.youtube.com/watch?v=07ds8iv1XPM"]
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The embed is responsive by default. It’ll appear like this:
You can specify the width and height if you'd like as well, as you can see below.
[youtube url="http://www.youtube.com/watch?v=TRmdXDH9b1s" width="100%" height="400"]