So the simple ingredients are:
Flashplayer.swf – This is what plays the embedded FLV
dhflashplayer.php – The MediaWiki extension (gets place in the “extension” directory)
The LocalSettings.php then gets modified to point to the dhflashplayer extension and that’s it. Now you use some special code to embed your video in MediaWiki. Something like this:
You can see the demo and view some more detailed instructions on the new UMW New Media Wiki.
For even more detail, I’ve created a screencast entitled How to Embed FLV Video in MediaWiki.