AS3 Flash

Loop mp3 in Flash

Oke, here come my problem. I’m trying to create a sound looping engine in Flash, and because I don’t want files to be embedded in the FLA (in the library) I only can use MP3 as a sound file which I can load dynamically.

I didn’t know this, but mp3 has a silence at the end of the song, and sometimes also at the beginning of the song (and sometimes both).
Other file, files without compression like WAV, don’t have this problem.

I don’t want to get to deep into this problem, but if you’re interested in the problem and you need to read more about it: about gapless playback: Gapless playback and LAME tech FAQ.

I remember from AS2 the looping problem, but I hoped it was fixed in AS3.
So this is what I tried to do:

A colleague of mine (Boy Wonder) gave me a beat so I could go to work.

#1 – First try

First convert the beat from WAV to MP3: I used Audacity, an open source software for recording and editing sound.

Oke, the only thing I needed is to load the file (because it’s a local test, there is no loading) and hear if it worked:

// AS3
private var url:String = "MySound.mp3";
private var song:SoundChannel;
var request:URLRequest = new URLRequest(url);
var soundFactory:Sound = new Sound();
song =, int.MAX_VALUE); 

No, it didn’t loop correctly

#2 – Second try

Open the newly generated MP3, and there they are: the silence at the beginning and at the end of the song. I could use Audacity to remove it, but I use another program for that: mptrim.

mpTrim is a simple and easy to use MP3 editor.

  • mpTrim can trim MP3s – removing silent or unwanted parts.
  • mpTrim can adjust the volume of MP3s. Volume change can be manual or automatic (volume normalization).
  • mpTrim can fade-in/out MP3s (to fix abrupt beginning/ending).
  • mpTrim can clean-up MP3s and recover wasted disk space.
  • mpTrim keeps the music quality intact, no matter how many times you process an MP3, because it works directly in the MP3 format without having to decode/re-encode. That also makes it very fast.

mpTrim has an auto function for removing silent, so that’s very easy.

But after loading the new mp3 without silence, the hiccup was much smaller, but still there.

#3 – Third try (neeeh forget it)

The last try would be to fix it in code: I was thinking about a earlier starting a loop (0.02 second) but with a lot of tracks this would probably be very cpu intensive.
A quick search on the Internet, I couldn’t find a solution in code. It’s a bug in Flash and people that are more into sound then I am, are working hard to move Adobe to change some of the sound features in Flash:


Because I have a hard head, and I need to make the same mistakes everyone makes….
But after all I have to conclude: It can’t be done, you will eventually get a hiccup in the loop.
It’s impossible to fix this problem.

So a dynamically loaded MP3 loops in flash will never work. The only way to get good loops is with WAV imported in the FLA (library) and use linkage