Slide 32
Slide 32 text
JavaScript Audio Write Example
Hz
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function AudioDataDestination(sampleRate, readFn) {
// Initialize the audio output.
var audio = new Audio();
audio.mozSetup(1, sampleRate);
var currentWritePosition = 0;
var prebufferSize = sampleRate / 2; // buffer 500ms
var tail = null;
// The function called with regular interval to populate
// the audio output buffer.
setInterval(function() {
var written;
// Check if some data was not written in previous attempts.
if(tail) {
written = audio.mozWriteAudio(tail);
currentWritePosition += written;
if(written < tail.length) {
// Not all the data was written, saving the tail...
tail = tail.slice(written);
return; // ... and exit the function.
}
tail = null;
}
// Check if we need add some data to the audio output.
var currentPosition = audio.mozCurrentSampleOffset();
var available = currentPosition + prebufferSize - currentWritePosition;
if(available > 0) {
// Request some sound data from the callback function.
var soundData = new Float32Array(available);
readFn(soundData);
// Writting the data.
written = audio.mozWriteAudio(soundData);
if(written < soundData.length) {
// Not all the data was written, saving the tail.
tail = soundData.slice(written);
}
currentWritePosition += written;
}
}, 100);
}
// Control and generate the sound.
var frequency = 0, currentSoundSample;
var sampleRate = 44100;
function requestSoundData(soundData) {
if (!frequency) {
return; // no sound selected
}
var k = 2* Math.PI * frequency / sampleRate;
for (var i=0, size=soundData.length; i<size; i++) {
soundData[i] = Math.sin(k * currentSoundSample++);
}
}
var audioDestination = new AudioDataDestination(sampleRate, requestSoundData);
function start() {
currentSoundSample = 0;
frequency = parseFloat(document.getElementById("freq").value);
}
function stop() {
frequency = 0;
}