watson-speech
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IBM Watson Speech to Text and Text to Speech SDK for web browsers.
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<h1 class="page-title">Source: media-element-audio-stream.js</h1>
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<pre class="prettyprint source linenums"><code>'use strict';
var Readable = require('stream').Readable;
var util = require('util');
/**
* Turns a MediaStream object (from getUserMedia) into a Node.js Readable stream and converts the audio to Buffers
*
* @see https://developer.mozilla.org/en-US/docs/Web/API/Navigator/getUserMedia
*
* @param {MediaStream|HTMLMediaElement} source - either https://developer.mozilla.org/en-US/docs/Web/API/MediaStream or https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaElement
* @param {Object} [opts] options
* @param {Number|null} [opts.bufferSize=null] https://developer.mozilla.org/en-US/docs/Web/API/AudioContext/createScriptProcessor
* @param {Boolean} [opts.muteSource=false] - If true, the audio will not be sent back to the source
*
* // todo: add option for whether to keep or destroy the context
*
* @constructor
*/
function MediaElementAudioStream(source, opts) {
opts = util._extend({
// "It is recommended for authors to not specify this buffer size and allow the implementation to pick a good
// buffer size to balance between latency and audio quality."
// https://developer.mozilla.org/en-US/docs/Web/API/AudioContext/createScriptProcessor
// Possible values: null, 256, 512, 1024, 2048, 4096, 8192, 16384
// however, webkitAudioContext (safari) requires it to be set
bufferSize: (typeof AudioContext != "undefined" ? null : 4096),
muteSource: false,
autoplay: true,
crossOrigin: "anonymous", // required for cross-domain audio playback
objectMode: true // true = emit AudioBuffers w/ audio + some metadata, false = emite node.js Buffers (with binary data only
}, opts);
// We can only emit one channel's worth of audio, so only one input. (Who has multiple microphones anyways?)
var inputChannels = 1;
// we shouldn't need any output channels (going back to the browser - that's what the gain node is for), but chrome is buggy and won't give us any audio without one
var outputChannels = 1;
Readable.call(this, opts);
var self = this;
var recording = true;
// I can't find much documentation for this for <audio> elements, but it seems to be required for cross-domain usage (in addition to CORS headers)
source.crossOrigin = opts.crossOrigin;
/**
* Convert and emit the raw audio data
* @see https://developer.mozilla.org/en-US/docs/Web/API/ScriptProcessorNode/onaudioprocess
* @param {AudioProcessingEvent} e https://developer.mozilla.org/en-US/docs/Web/API/AudioProcessingEvent
*/
function processAudio(e) {
// onaudioprocess can be called at least once after we've stopped
if (recording) {
// todo: interleave channels in binary mode
self.push( opts.objectMode ? e.inputBuffer : new Buffer(e.inputBuffer.getChannelData(0)) );
}
}
var AudioContext = window.AudioContext || window.webkitAudioContext;
// cache the source node & context since it's not possible to recreate it later
var context = source.context = source.context || new AudioContext();
var audioInput = source.node = source.node || context.createMediaElementSource(source);
var scriptProcessor = context.createScriptProcessor(opts.bufferSize, inputChannels, outputChannels);
scriptProcessor.onaudioprocess = processAudio;
if (!opts.muteSource) {
var gain = context.createGain();
audioInput.connect(gain);
gain.connect(context.destination);
}
/**
* Setup script processor to extract audio and also re-connect it via a no-op gain node if desired
*
* Delayed to avoid processing the stream of silence received before the file begins playing
*
*/
function connect() {
audioInput.connect(scriptProcessor);
// other half of workaround for chrome bugs
scriptProcessor.connect(context.destination);
source.removeEventListener("playing", connect);
}
source.addEventListener("playing", connect);
// https://developer.mozilla.org/en-US/docs/Web/Guide/Events/Media_events
// https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaElement/readyState
function start() {
source.play();
source.removeEventListener("canplaythrough", start);
}
if (opts.autoplay) {
// play immediately if we have enough data, otherwise wait for the canplaythrough event
if(source.readyState === source.HAVE_ENOUGH_DATA) {
source.play();
} else {
source.addEventListener("canplaythrough", start);
}
}
function end() {
recording = false;
scriptProcessor.disconnect();
audioInput.disconnect();
//context.close(); // this prevents us from re-using the same audio element until the page is refreshed
self.push(null);
self.emit('close');
}
source.addEventListener("ended", end);
this.stop = function() {
source.pause();
end();
};
source.addEventListener("error", this.emit.bind(this, 'error'));
process.nextTick(function() {
// this is more useful for binary mode than object mode, but it won't hurt either way
self.emit('format', {
channels: 1,
bitDepth: 32,
sampleRate: context.sampleRate,
signed: true,
float: true
});
});
}
util.inherits(MediaElementAudioStream, Readable);
MediaElementAudioStream.prototype._read = function(/* bytes */) {
// no-op, (back-pressure flow-control doesn't really work on sound)
};
/**
* Converts a Buffer back into the raw Float32Array format that browsers use.
* Note: this is just a new DataView for the same underlying buffer -
* the actual audio data is not copied or changed here.
*
* @param {Buffer} chunk node-style buffer of audio data from a 'data' event or read() call
* @return {Float32Array} raw 32-bit float data view of audio data
*/
MediaElementAudioStream.toRaw = function toFloat32(chunk) {
return new Float32Array(chunk.buffer);
};
module.exports = MediaElementAudioStream;
</code></pre>
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<h2><a href="index.html">Home</a></h2><h3>Classes</h3><ul><li><a href="FormatStream.html">FormatStream</a></li><li><a href="MediaElementAudioStream.html">MediaElementAudioStream</a></li><li><a href="RecognizeStream.html">RecognizeStream</a></li><li><a href="TimingStream.html">TimingStream</a></li><li><a href="WebAudioL16Stream.html">WebAudioL16Stream</a></li></ul><h3>Events</h3><ul><li><a href="RecognizeStream.html#event:connection-close">connection-close</a></li><li><a href="RecognizeStream.html#event:data">data</a></li><li><a href="RecognizeStream.html#event:error">error</a></li><li><a href="RecognizeStream.html#event:results">results</a></li></ul>
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