(AS3) playing multiple flv's/ resource management

programming flash
1

i have 3 flvs, that are rather big in dimension, that im using as backgrounds. when i use any of these flvs my movie works fine but when i switch to a new background my movie takes a big hit in performace. im guessing this has something to do with the garbage collection in as3 because i explicitly get rid of the old background. what is the best way to cycle through multiple flvs without loosing performance?

heres code im using to switch backgrounds

removeChild(theBackground);
				theBackground = null;
				
				theBackground = assetLoader.getBackground(level);
				addChildAt(theBackground,1);

and heres code im using to play flvs

public function populate():void{
			var nc:NetConnection = new NetConnection();
			nc.connect(null);
			 
			var ns:NetStream = new NetStream(nc);
			 
			var vid:Video = new Video(1224,840);
			this.addChild(vid);

			vid.attachNetStream(ns);
			
			ns.play("bg2Blue.flv");
			ns.addEventListener(NetStatusEvent.NET_STATUS, netstat);
			
			function netstat(stats:NetStatusEvent){
			        trace(stats.info.code);
			}
			 
			var netClient:Object = new Object();
			netClient.onMetaData = function(meta:Object){
			        trace(meta.duration);
			};
			ns.client = netClient;
			
			trace("populated.");
		}