AS3 ExternalInterface.addCallback

1. In the Flash add the following method with to parameters.

ExternalInterface.addCallback(functionName, parameters)

functionName: this is the function name in the javascript.
parameters: parameters you might need for that function.

example:
ExternalInterface.addCallback('tellFlashToPlay','playVideo');
ExternalInterface.addCallback('tellFlashToPause','pauseVideo');

2. create the functions within Flash

private function playVideo():void
{
video.play();
}  


private function pauseVideo():void
{
video.pause();
} 

3. create functions in javascript to call Flash.

function getFlashMovie(movieName) {
  var isIE = navigator.appName.indexOf("Microsoft") != -1;
  return (isIE) ? window[movieName] : document[movieName];
}

4. on click call functions in flash:

getFlashMovie("nameOfFlashMovie").tellFlashToPlay();


getFlashMovie("nameOfFlashMovie").tellFlashToPause();

links:
http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/external/ExternalInterface.html#addCallback() 


http://www.viget.com/inspire/bi-directional-actionscript-javascript-communication/