Load an audio file into a Float32Array using Audio Data API

moz-load-file.js

function mozLoadFile (url, callback) {
	function throwAsync (err) {
		setTimeout(function () {
			callback(typeof err === 'string' ?
				Error(err) : err);
		}, 0);
	}

	function onaudioavailable (e) {
		loadedmetadata();

		var n, b, i, m;

		for (n=0; n<channelCount; n++) {
			b = new Float32Array(frameBufferLength / channelCount);
			buffers[n].push(b);

			for (i=n, m=0; i<frameBufferLength; i+=channelCount, m++) {
				b[m] = e.frameBuffer[i];
			}
		}

		length += frameBufferLength / channelCount;
	}

	function loadedmetadata () {
		if (isMetaDataLoaded) {
			return;
		}

		sampleRate = audio.mozSampleRate;
		channelCount = audio.mozChannels;
		frameBufferLength = audio.mozFrameBufferLength;

		for (var n=0; n<channelCount; n++) {
			buffers.push([]);
		}

		isMetaDataLoaded = true;
	}

	function onended () {
		var i, b, d, o;

		for (i=0; i<channelCount; i++) {
			b = new Float32Array(length);
			o = 0;

			while (d = buffers[i].shift()) {
				b.subarray(o, o + d.length).set(d);
				o += d.length;
			}

			buffers[i] = b;
		}

		callback(undefined, {
			sampleRate: sampleRate,
			samples: buffers
		});
	}

	var audio = document.createElement('audio');
	var length = 0;
	var buffers = [];
	var sampleRate = 0;
	var channelCount = 0;
	var isMetaDataLoaded = false;
	var frameBufferLength = 0;

	if (!audio.mozSetup) {
		throwAsync("No Audio Data API");
		return;
	}

	audio.addEventListener('MozAudioAvailable', onaudioavailable, false);
	audio.addEventListener('loadedmetadata', onloadedmetadata, false);
	audio.addEventListener('ended', onended, false);
	audio.addEventListener('error', throwAsync, false);

	audio.muted = true;
	audio.src = url;
	audio.play();
}

In onaudioavailable():

for (i=n; i<frameBufferLength; i+=channelCount) {
    b[Math.floor(i/channelCount)] = e.frameBuffer[i];
}

Ahhh, I shouldn't have tested with a mono file. Should be fixed now, but I'm not sure, because I optimized it a bit. :P

Yep, your code works fine. I knew mine was a hack.