Basics first. How to make your symbol from Flash library visible for Flex (see images on the bottom of the artice):

• 1. Create your symbol and linkage (library (Ctrl+L) / {your symbol} / Linkage…).
• 2. Linkage Properties, set your class name that will be used in [Embed] meta.
• 3. Export .swf file and make Assets.as.

It is very handy to use central assets class. This is how I make my assets accessible in Flex application:

package
{
    import mx.core.SpriteAsset;

    public class Assets extends Object
    {
        // change/to/your/uber/cool/path/and/filename.whatsoever
        // you can also embed graphic files (.jpeg, .png, )
        [Embed(source="../libs/assets.swf#symbol1")]
        public static const symbol1Class:Class;
        public static const symbol1SpriteAsset:SpriteAsset = new symbol1Class();

        [Embed(source="../libs/assets.swf", symbol="symbol2")]
        public static const symbol2Class:Class;

        // embedding Bitmap
        [Embed(source="../libs/image.png")]
        public static const imageClass:Class;
        public static const imageBitmap:Bitmap = new imageClass();

        public function Assets()
        {
            super();
        }
    }
}

There are two ways how to ask for your symbol from .swf library – 1. source=”…#symbol1″ or 2. source=”…” symbol=”symbol2″. Symbol name is whatever you set in Linkage Properties Class in Flash (not symbol name in library!).

Usage example:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="horizontal" applicationComplete="init()">
<mx:Script>
<![CDATA[
    import Assets;

    private function init():void
    {
        container1.setStyle("backgroundImage", Assets.symbol1Class);
        container2.setStyle("backgroundImage", Assets.symbol2Class);
        container3.addChild(Assets.symbol1SpriteAsset);
    }
]]>
</mx:Script>
<mx:Box id="container1" width="100" height="100"/>
<mx:Box id="container2" width="100" height="100"/>
<mx:UIComponent id="container3" width="100" height="100"/>
</mx:Application>

Embedding proccess and example result in images:

Flash linkage symbol

Flash linkage properties

Flex embedded symbols