Hey Andrew,
You're welcome.
I already consult with our developer regarding this. In Easyblog 5 already took out this video embed for legacy post (3.9 old post/create post in Joomla default editor) is because Joomla default editor itself already got their own video embed feature.
If they use tinymce, they can select this option to embed the video link :
http://screencast.com/t/5UmReKfRSSw
If they use JCE, they can copy the youtube embed code then paste in blog content. Check my screenshot below.
// embed code
<iframe width="560" height="315" src="https://www.youtube.com/embed/O4IRqFee7k4" frameborder="0" allowfullscreen></iframe>