How to check in AS3 if embedded movie finished playing

I am writing an application in AS3. The application first plays an external intro swf file and then continues. I make the intro in Flash CS3.

The question is: how my AS3 application will know that the intro has finished? What is the correct way to do it?

One of my first ideas was to create a timer event in AS3 and start the timer and intro at the same moment. But in this case I would need to know the length of the intro, which is bad because intro is supposed to change.

Next idea is to make the intro to dispatch the event “intro_finished” which I could listen to in AS3 application and continue when received. But I have not found a way to make an event class in Flash authoring environment, seems that no class definition is allowed.

So… is it possible at all to check when the embedded movie finished?