Dynamically Generated Audio Garbling - actionscript-3

Question

I've created the standard player for dynamic sounds in a web app like so:
var _dynamicAudio:Vector.<Number> = new Vector.<Number>();
var _sampleIndex:uint = 0;
// ..Code to generate '_dynamicAudio' samples omitted
var _sound:Sound = new Sound();
_sound.addEventListener(SampleDataEvent.SAMPLE_DATA, onSampleDataEvent);
_sound.play();
function onSampleDataEvent(event:SampleDataEvent):void {
var samplesRead:int = 0;
while (samplesRead <= 8192 && _sampleIndex < _dynamicAudio.length) {
var sample:Number = _dynamicAudio[_sampleIndex];
event.data.writeFloat(sample);
event.data.writeFloat(sample);
_sampleIndex++;
_samplesRead++;
}
}
However, on slower computers (or if I stress my own by opening other applications) the audio tends to 'garble' occasionally. It sounds like it gets stuck looping over a block of the most recent samples. When this happens, I've noticed that event.position jumps by some multiple of 8192, which would also seem to imply that onSampleDataEvent isn't being called for a few consecutive chunks of samples. If that's true, it would seem this issue is unavoidable. What I'd like to know is if there's any way to detect the garbling before it happens so I can pause the audio in place of the awful noise? Thanks!

Answer 1

It might be that the while() loop is heavy and you don't always have the memory/CPU power to process it. So it freezes and gives you the effect you described.
It might be possible to break up the loop into smaller loops, thus evening out the CPU load. At the same time processing the event far ahead enough to seamlessly playback the audio.
The following code is not tested and is only an example of how breaking up a loop could look like:
var _dynamicAudio:Vector.<Number> = new Vector.<Number>();
var _sampleIndex:uint = 0;
// ..Code to generate '_dynamicAudio' samples omitted
var _sound:Sound = new Sound();
_sound.addEventListener(SampleDataEvent.SAMPLE_DATA, onSampleDataEvent);
_sound.play();
function onSampleDataEvent(event:SampleDataEvent):void {
var samplesRead:int = 0;
writeSamples(0, event);
}
function writeSamples(counter:int, eventReference:SampleDataEvent):void
{
var startTime:int = getTimer();
while (samplesRead <= (8192 - counter) && _sampleIndex < _dynamicAudio.length)
{
// check if the processing takes too long
if (getTimer() - startTime > 5)
{
writeSamples(counter, eventReference);
break;
}
counter++;
var sample:Number = _dynamicAudio[_sampleIndex];
event.data.writeFloat(sample);
event.data.writeFloat(sample);
_sampleIndex++;
_samplesRead++;
}
}
The main idea of the previewed code is to:
1) Check if the while loop is executed for too long. In my example 5ms is the limit
2) Break the loop if the execution is too long and start the loop again from the place it was stopped at.
If the whole process takes less than the limit, the loop will finish in one go.
You may want to refactor the code as it is not optimized and creates a lot of garbage instead of reusing objects.