oEmbed was designed to avoid making copy and paste HTML from the site hosting the media. It supports videos, images, text, and more.
WordPress will automatically turn that into a YouTube embed when the post is viewed. For enabling auto embed check the “Auto-embeds” check box in Dashboard->Settings->Media SubPanel.
You can also wrap URL in the shortcode. It accomplish same effect, but does not require the URL to be on its own line and the "Auto-embeds" setting to be enabled.</p>
<p style="text-align: justify">It allows you to set a maximum (but not fixed) width and height, For example:</p>
<p style="text-align: justify">…