/
app-media-audio.js
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/
app-media-audio.js
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/**
@license
Copyright (c) 2017 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at
http://polymer.github.io/LICENSE.txt The complete set of authors may be found at
http://polymer.github.io/AUTHORS.txt The complete set of contributors may be
found at http://polymer.github.io/CONTRIBUTORS.txt Code distributed by Google as
part of the polymer project is also subject to an additional IP rights grant
found at http://polymer.github.io/PATENTS.txt
*/
import {Polymer} from '@polymer/polymer/polymer-legacy.js';
/**
`app-media-audio` is an element that converts an audio source to an audio
analyser suitable for generating audio visualizations such as the ones made by
`app-media-waveform`.
@demo demo/index.html
*/
Polymer({
is: 'app-media-audio',
/** @override */
_template: null,
properties: {
/**
* The input source for the element. This can be a Media Stream or a
* Media Element (such as an audio or video element).
*
* @type {MediaStream|HTMLMediaElement}
*/
source: {type: Object},
/**
* The audio context that the analyser is associated with.
*
* @type {AudioContext}
*/
context: {
type: Object,
readOnly: true,
value: function() {
if (window.AudioContext) {
// chrome requires class to be constructed directly
return new AudioContext();
} else if (window.webkitAudioContext) {
// prefix for safari
return new webkitAudioContext();
}
return null;
}
},
/**
* An AnalyserNode that is linked to the audio input source.
* https://developer.mozilla.org/en-US/docs/Web/API/AnalyserNode
*
* @type {AnalyserNode}
*/
analyser:
{type: Object, notify: true, computed: '_computeAnalyser(context)'},
/**
* An AudioNode that is associated with the audio source.
*
* @type {MediaStreamAudioSourceNode|MediaElementAudioSourceNode}
*/
sourceNode: {
type: Object,
notify: true,
computed: '_computeSourceNode(context, source, analyser)',
observer: '_sourceNodeChanged'
}
},
_computeSourceNode: function(context, source, analyser) {
if (context == null || source == null || analyser == null) {
return;
}
// NOTE(cdata): The source can be either an HTMLVideo element (that
// happens to have audio tracks) or a MediaStream.
if (source instanceof MediaStream) {
if (source.getAudioTracks().length === 0) {
this._warn(this._logf('Media Stream does not have any audio tracks!'));
}
return context.createMediaStreamSource(source);
} else {
return context.createMediaElementSource(source);
}
},
_computeAnalyser: function(context) {
var analyser = context.createAnalyser();
// NOTE(cdata): Size of the fast fourier transform that determines the
// frequency domain
analyser.fftSize = 2048;
return analyser;
},
_sourceNodeChanged: function(sourceNode, oldSourceNode) {
if (oldSourceNode != null) {
oldSourceNode.disconnect(this.analyser);
}
if (sourceNode != null) {
sourceNode.connect(this.analyser);
}
}
});