Save streamed MP3 file?

Unless you can find an MP3 encoding library that could take the extract() data and convert it back with minimal effort, I think your only option is to save the mp3 using the File and FileStream classes. One thing you could try is to use a File object to download the file, and while it is downloading, you have the sound object play the data contents of the File object downloading the mp3. I just tried a quick test locally and it worked on my desktop. You will have to try it from an actual server to know how well it can work in that environment, but it is at least worth a shot.

import flash.filesystem.File;
import flash.filesystem.FileMode;
import flash.filesystem.FileStream;
import flash.events.ProgressEvent;
import flash.events.Event;
import flash.media.Sound;
import flash.net.URLRequest;

var file:File = File.applicationDirectory.resolvePath("gravity.mp3");
file.addEventListener(ProgressEvent.PROGRESS, onProgressEvent);
file.addEventListener(Event.COMPLETE, onFileLoadComplete);
file.load();

var sound:Sound;

function onProgressEvent(e:ProgressEvent):void {
  if (sound == null) {
  file.removeEventListener(ProgressEvent.PROGRESS, onProgressEvent);
  sound = new Sound(new URLRequest(file.url))
  sound.play();
  }
}

function onFileLoadComplete(e:Event):void {
  file.removeEventListener(Event.COMPLETE, onFileLoadComplete);

  var saveFile:File = File.desktopDirectory.resolvePath("gravity2.mp3");
  var fs:FileStream = new FileStream();
  fs.open(saveFile, FileMode.WRITE);
  fs.writeBytes(file.data, 0, file.data.length);
  fs.close();
}

What this code is doing is creating a File object with, in this case, a path to an MP3 in the same folder as the test FLA I created. This would be a path to your server stored MP3. Then you setup the event listeners for progress and complete. I used progress to know that the file had actually started to be downloaded to then trigger the initialization of my Sound object. Depending on someones network connection and the size of the MP3, it could be a good idea to use progress to know that the file has gotten X percentage done before trying to play the file.

For testing purposes in my progress event, I just checked to see if the Sound object had been initialized yet, and if it hadn't then set sound equal to a new Sound object with the File.url property for the URLRequest() and then told it to play.

Once the File object dispatched the complete event to indicate that the download finished, I created a new File object for the purpose of saving it to the filesystem using the FileStream class. Using FileStream to save the file allows for no user interaction to save the MP3.

There may be better ways to handle my method, but I can't think of any at the moment. As far as I know, the second File object, which I named "saveFile", is required in order to actually save the downloaded MP3 object because Im not too familiar with File manipulation. The only downside I can think of is that you have a copy of the MP3 is memory and would need to null out the File object that loaded the MP3 to free up memory.