Yeah, I will promise you that you will have a hell of a time isolating that part of the code from a full-blown CMS. Even if the code is in a plugin, the API that was used to create the plugin will cause you too to be familiar with phpmotions api. Unless you plan on switching your site over to phpmotion for everything, you may be in for a bumpy road.
Another important thing to note is that you will most likely have to transcode the video which is very CPU intensive and time consuming (convert that mpeg to flv.) Youtube seems to batch this on another server while you wait, so you may be looking at additional hardware. Also, video files are naturally much larger than images as you well know. You will have memory limits being hit. Scripts and database timeouts and possible other difficulties to contend with.
I don't mean to be discouraging but the issues I raise above are the reason I suggested the Youtube API in the first place.
Good luck!