It is very easy!
First you need to find out the video ID (xxxxx) for Youtube, Soapbox and Google, then in your post, just type [PYoutube:xxxxx], or [PSoapbox:xxxxx], or [PGooglevideo:xxxxx] to embed videos from those sources in your post.
Note: You need to remove the "P" in the [ above because If I remove "P", it will display a video.
How to find Youtube ID?