March 20th, 2009
Second steps with Flash 10 audio programming
A while back I did some experimenting with the new Flash 10 audio features. Since then I’ve received a couple of emails from people who have noticed that the flash player can freeze up when the mp3 file is initially extracted with the Sound.extract command – especially with longer mp3 files.
The solution is to simply extract only as much of the sound as you need to work with on each sampleData callback. However, this can get confusing when you combine it with the speed changing code from my first example. So I’ve put together another example which uses this method:
The code is available for download here or you can see it below:
{
import flash.events.Event;
import flash.events.SampleDataEvent;
import flash.media.Sound;
import flash.media.SoundChannel;
import flash.net.URLRequest;
import flash.utils.ByteArray;
/**
* @author Kelvin Luck
*/
public class MP3Player
{
public static const BYTES_PER_CALLBACK:int = 4096; // Should be >= 2048 && < = 8192
private var _playbackSpeed:Number = 1;
public function set playbackSpeed(value:Number):void
{
if (value < 0) {
throw new Error('Playback speed must be positive!');
}
_playbackSpeed = value;
}
private var _mp3:Sound;
private var _dynamicSound:Sound;
private var _channel:SoundChannel;
private var _phase:Number;
private var _numSamples:int;
public function MP3Player()
{
}
public function loadAndPlay(request:URLRequest):void
{
_mp3 = new Sound();
_mp3.addEventListener(Event.COMPLETE, mp3Complete);
_mp3.load(request);
}
public function playLoadedSound(s:Sound):void
{
_mp3 = s;
play();
}
public function stop():void
{
if (_dynamicSound) {
_dynamicSound.removeEventListener(SampleDataEvent.SAMPLE_DATA, onSampleData);
_channel.removeEventListener(Event.SOUND_COMPLETE, onSoundFinished);
_dynamicSound = null;
_channel = null;
}
}
private function mp3Complete(event:Event):void
{
play();
}
private function play():void
{
stop();
_dynamicSound = new Sound();
_dynamicSound.addEventListener(SampleDataEvent.SAMPLE_DATA, onSampleData);
_numSamples = int(_mp3.length * 44.1);
_phase = 0;
_channel = _dynamicSound.play();
_channel.addEventListener(Event.SOUND_COMPLETE, onSoundFinished);
}
private function onSoundFinished(event:Event):void
{
_channel.removeEventListener(Event.SOUND_COMPLETE, onSoundFinished);
_channel = _dynamicSound.play();
_channel.addEventListener(Event.SOUND_COMPLETE, onSoundFinished);
}
private function onSampleData( event:SampleDataEvent ):void
{
var l:Number;
var r:Number;
var p:int;
var loadedSamples:ByteArray = new ByteArray();
var startPosition:int = int(_phase);
_mp3.extract(loadedSamples, BYTES_PER_CALLBACK * _playbackSpeed, startPosition);
loadedSamples.position = 0;
while (loadedSamples.bytesAvailable > 0) {
p = int(_phase - startPosition) * 8;
if (p < loadedSamples.length - 8 && event.data.length <= BYTES_PER_CALLBACK * 8) {
loadedSamples.position = p;
l = loadedSamples.readFloat();
r = loadedSamples.readFloat();
event.data.writeFloat(l);
event.data.writeFloat(r);
} else {
loadedSamples.position = loadedSamples.length;
}
_phase += _playbackSpeed;
// loop
if (_phase >= _numSamples) {
_phase -= _numSamples;
break;
}
}
}
}
}
You can compare it to the code in the original post to see the changes I made.
One thing to note is that there is still a delay when you load an MP3 in my example. This is because I am using the same FileReference.browse > Sound object hack as last time and this needs to loop over the entire loaded mp3 file while turning it into a Sound object. This wouldn’t be an issue in most use-cases where you have loaded the sound through Sound.load.
I also removed the option of playing the sound backwards in this example as that would have added further complexity to the code and hurt my head even more!
In: AS3, flash, flex | tags: AS3, audio, flash10, sourcecode. | #
49 Comments, Comment or Ping
1.
G thanks :)
2.
you calculate:
_numSamples = int(_mp3.length * 44.1);
on each sample-event - so it is pretty lousy for memory..
just do it once on the constructor (or the loadComplete handler..)
3.
another thanks..
April 5th, 2009
Hi,
1.
No worries :)
2.
Hmmm - no I don't! That line is in the play() method which is only called once - when the sound has completed loading... The onSampleData method is called on each SampleDataEvent... Also, calculating that number each time wouldn't effect memory usage, it would however be (slightly) detrimental to performance...
But... Thanks for making me look at the code again... I just noticed that there was some redundant code in the playLoadedSound function which was slowing things down lots (I'd forgotten to remove the code which extracted the whole sound up-front). I've updated the code above and in the zip file. If you want to compare it to the broken code that was first on this post, that is still available here. The delay when you load an mp3 file is now very much reduced!
3.
No worries :) Thanks for making me look again and notice my glaring error!
April 5th, 2009
I use this class for play 32000Hz sound ,the speed is too fast.
April 6th, 2009
Hi Days,
I'm not sure of the solution for you. Did you try changing this line:
_numSamples = int(_mp3.length * 44.1);
To be * 32 instead?
The Adobe docs state: "The audio data is always exposed as 44100 Hz Stereo" so I guess it should already be 44.1kHz by the time it's extracted...
Hope that helps,
Kelvin :)
April 6th, 2009
Hi Kelvin,
Is it possible to slow down the playback without changing the pitch?
Cheers
April 22nd, 2009
Hey Daniel,
This is possible - but not without changing the code quite a bit. What you are after is called "time stretching" and is fairly complex to achieve. I did some research into it a while back but I never got around to implementing it in flash... If you google timestretching you should be able to find descriptions of the algorithms and some opensource code (in c and maybe java) - hopefully that will help.
Good luck!
Kelvin :)
April 22nd, 2009
Hey Kelvin:
This is suprer. I am working on an application that needs to vary the playback speed of an mp3 file but keep the pitch constant. Since I don't deal with mp3 everyday, I am really clueless on how to accomplish this. Do you have any thought you could pass along? Thanks
Chris
April 27th, 2009
Hi Chris,
You also need "time stretching" - see the comment directly above yours.
Cheers,
Kelvin :)
April 28th, 2009
Hi Kelvin. Your article has inspired the sound of my new flash game !
I have a motor loop sound of 2 seconds.
Using your class the loop never re-start because this conditional is never called:
if (phase >= numSamples) {
phase -= numSamples;
break;
}
When I trace the phase and numSamples, the last result is this:
91008, 92160
So I needed to add a line in your "onSoundFinished" method, to restart the phase.
private function OnSoundFinished(event:Event):void
{
phase = 0; channel.removeEventListener(Event.SOUND_COMPLETE, OnSoundFinished);
channel = dynamicSound.play();
channel.addEventListener(Event.SOUND_COMPLETE, OnSoundFinished);
}
It works that way, but I want to ask you if I´m doing anything wrong. Maybe the sound file has any problem? (it´s a 44100 hz mp3)
May 4th, 2009
Hi Xleon,
Sorry for the slow reply...
That's strange that I haven't run into that problem. Maybe it's to do with the specific length of your mp3 file? I've tried with a number of mp3 files and never had any problems... A 44.1 KHz mp3 should work fine...
Maybe you can email me your mp3 file and I'll test at my end?
May 17th, 2009
Kevin,
I believe you had code for working with mp3 and cue points. I can't seem to find it, can you bring it back?
June 12th, 2009
Hi Rick,
I'm afraid I'm not sure what you are talking about! It must have been someone else who had the code you are looking for?
June 12th, 2009
hello kevin,
is it possible to make your App to work with an ogg file format ?
chears !
:)
July 4th, 2009
Hi,
Unfortunately it won't work with the ogg file format as flash doesn't support it natively. This link may help you out though:
barelyfocused.net/blog/2008/10/03/flash-vorbis-player/
Cheers,
Kelvin :)
July 5th, 2009
Hi Kelvin,
sorry for bother you again,
like row sound we put buffer, like this
buffer = new SoundLoaderContext(65000);
_loop_snd = new Sound(new URLRequest(_mp3), buffer);
how can i put buffer in dynamic sound..as per your code where i can put buffer in below code..
any suggestion,
_dynamicSound = new Sound(); _dynamicSound.addEventListener(SampleDataEvent.SAMPLE_DATA, onSampleData);
thanks in advance, waiting for your reply..
July 14th, 2009
HI,
The buffer would make no sense in the context of my code because my code loads the entire mp3 before beginning the playback. I haven't investigated if it's possible to work with an incompletely loaded mp3 but I guess you could if you listen to the progress events as it loads and implement your own logic for tracking how much of the sound has loaded etc. It's not trivial though...
Hope that helps,
Kelvin :)
July 15th, 2009
Hi Kelvin
Thanks for the prompt reply,
i already wrote some logic of play buffered mp3 with dynamic sound, but in that one problem is occur if mp3 files bytes loaded 5000 and my trackBarKnob reach at 5000 bytes and again for downloading bytes it's take some seconds in that time it's play song from stating.(if Internet connection is very slow than this problem occurs).
Sorry for my the English, hope you understand
Thanks
Bechar
July 16th, 2009
Hi Bechar,
It sounds like one of two things is going wrong. Either the Event.SOUND_COMPLETE is firing when the buffer is empty (and this would cause the sound to loop). Or the calculation of _numSamples is incorrect because the .length of the mp3 isn't correct until the mp3 is fully loaded. To start debugging you will first need to figure out which of these things is causing the problem,
Hope that helps,
Kelvin :)
July 19th, 2009
Hi Kelvin,
Thanks for your reply, i will try for the same you explaine in the blog and let you know, how it's figure it out, thanks for your support.
Thanks
Bechar Kanjariya
July 20th, 2009
Hi there!
I've been trying to understand what's been said in the last few comments to figure out if they relate to my question, but I'm still not sure.
I have a question about the inital playback of a sound when using sampleDataEvent.
Let me explain..
I've started developing games for flash. I made this game, for example:
www.kongregate.com/games/TackleMcClean/memory-mayhem
A somewhat simple card matching game, but I've strived for perfection in it. One huge pain was handling audio. During development I had sessions where I would click the cards, and they would play the "card folding" sound. Problem was that it was off, timewise. If I clicked two cards quickly after each other, the first sound was delayed, but the second was usually spot on.
This led to some extensive testing on my end:
Using setInterval on a function that simply plays a short sound gave VERY unpleasant results. It is VERY uneven and jumps back and forth in time, usually ending up in a "shuffling" (in drumming) kind of playback.
Comparing this to just calling play() and having it loop (with the second parameter), it's night and day. Looping by play() is supertight.
Today I finally got around testing things with your approach, MINUS the time-control. Just play a sound and then loop back. So in essence, reinvent the wheel that is the play function, or at least complicating it. I didn't give me anything tangible other than more understanding on how the sound playback works in flash.
The results were that if I looped the sound when playing back by writing directly to the data of the SampleDataEvent, it was silky smooth just like the play() looping. Kind of expected.
EXCEPT... it was NOT smooth just when the looping started. It makes a short stuttering.
So here's the question:
Do you know any way to put a very short sound in a buffer so it can be instantly played?
If that could be achieved, then having a custom play method that plays a sound using that method, should theoretically survive being used by the setInterval method. If it doesn't, it doesn't really matter since the main application for this is game development use.
I've seen this issue coming and going but never solved. People having trouble with simple interfaces; a sound plays when mouse rolls over a button for example, but it doesn't sync up with that the user is actually doing on screen (not until the second time the sound plays at least).
It would be of great use, and if you have just the littlest bit of insight that could push me in the right direction I'll whip up something easy to understand for the average joe and post wherever people have the problem :D
If you've read this whole message then you deserve a beer.
July 21st, 2009
Hi Karl,
Wow - that's a coincidence! Last year I wrote a game called Multiplayer Memory Mayhem!
www.kelvinluck.com/2008/10/new-multiplayer-papervision-game/
Re. delays in triggering sounds for interface variations, I can't say I have ever run into this problem. I presume that you are calling load on the sound up front and then just calling play when your UI interaction happens? And there is a delay first time it's played? You could maybe play it once with the volume set to 0 after loading it (if it is always the first time that causes problems). Then the first time the UI triggered it it would already have played once so would come quicker?
Alternatively you could have a sound constantly playing with a SampleDataEvent callback like my examples above. You would fill the data with zeros (for silence) until the UI interaction happened and then that could set a flag to use something other than zeros. Does that make sense? Then there would be no "startup" delay cos the sound would already be playing...
Hope that helps,
Kelvin :)
July 30th, 2009
Hey Kelvin!
I've even been to your blog before sometimes, but I didn't know you made that game.
Last week I was googling to see if I could find my own game (which btw is taken off from Kongregate.com at the moment due to upcoming licensing and whatnot).
I found your game then, and I was thinking about making a multiplayer version of my game, which I would incidentally call "Multiplayer Memory Mayhem". I suppose we both chose a name that should appease to the public :)
What's even more fun is that I remember reading your blog post about the game and looking at the 3d transitions for the score, but I took no (concious, at least) note of the name of the game.
Anyways,
to best see