Fai un trace per sapere quanti frames hanno gli swf
codice:
loadMovieNum("movie1.swf",1);
loadMovieNum("movie2.swf",2);
_root.onEnterFrame = function(){
  trace(_level1._currentframe)
  trace(_level2._currentframe)
}
Metti che ne abbiano 20
codice:
_root.onEnterFrame = function(){
  if(_level1._currentframe < 20){
  _level2.stop();
  }
  if(_level1._currentframe == 20){
  _level2.play();
  }
}