For post a video, you needn't to enable HTML.
Go in your ACP
> Configuration > Icy Phoenix > Posting & Messages
And there, enable " Allow BBCode for Active Content in posts ". It will allow your users to link and stream videos on your site. If you want to ALLOW them to upload themselves the video they want to display, you will need to install Media Mod
made by DWho.
I hope that's what you asked for.