As you may already know, if not this is done , you can now embedded some HTML code on your SharePoint pages (available on SharePoint 2013 and SharePoint Online); especially on blog post.
To do so, just create a new blog post (or page) and use the Insert tab and Embed Code button.
However, there is some security settings associated with this option.
I ran onto an issue when I tried to embedded a Slideshare presentation I just uploaded earlier.
This HTML cannot be inserted because this type of content is not allowed.
After digging a little bit on this issue, the security settings associated with the embedded code option is available at the Site Settings\Site Collection Administration\HTML Field Security option
When you go there, you can allow/disallow embedded code and then if allowing, manage from which domain embedded code is allowed. By default, there is only YouTube, Bing, Skydrive and Office.