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@jussi-kalliokoski
Created October 6, 2011 11:47
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Methods for creating an audio tag filled with a specified time of silence.
(function(g){
var urlPath =
window.URL ? 'URL' :
window.webkitURL ? 'webkitURL' :
window.mozURL ? 'mozURL' :
window.msURL ? 'msURL' :
window.oURL ? 'oURL' : '';
var blobPath =
window.BlobBuilder ? 'BlobBuilder' :
window.WebKitBlobBuilder ? 'WebKitBlobBuilder' :
window.MozBlobBuilder ? 'MozBlobBuilder' :
window.MSBlobBuilder ? 'MSBlobBuilder' :
window.OBlobBuilder ? 'OBlobBuilder' : '';
var char = String.fromCharCode;
function dWord(w){
return char(0x000000FF & w) +
char((0x0000FF00 & w) >> 8) +
char((0x00FF0000 & w) >> 16) +
char((0xFF000000 & w) >> 24) ;
}
function sWord(w){
return char(0x00FF & w) +
char((0xFF00 & w) >> 8);
}
/**
* Creates a dynamic url of the supplied data, using Blob URLs where available, falling back to Data URLs.
*
* @param {String} data The data to create the dynamic URL from.
* @param {String} mime The mime type of the data (default: application/octet).
*/
function DynUrl(data, mime){
var bb;
this.mime = mime || this.mime;
/* Try to use Blob URLs */
if (/* OK, it's not working for some reason, <FIXME> */0&&/* /* </FIXME> */urlPath && blobPath){
bb = new window[blobPath]();
bb.append(data);
this.url = window[urlPath].createObjectURL(bb.getBlob());
this.type = 'blob';
/* Fall back to Data URLs */
} else {
this.url = 'data:' + mime + ';base64,' + btoa(data);
}
}
DynUrl.prototype = {
url: null,
mime: 'application/octet',
type: 'data',
revoke: function(){
switch (type){
case 'blob':
window[urlPath].revokeObjectURL(this.blob); break;
default:
/* Nothing to do here. */
}
},
toString: function(){
return this.url;
}
};
/**
* Generates an audio element of specified duration of silence.
*
* @param {Number} duration Duration of silence in seconds (default: 5).
* @return {Audio} The generated audio element.
*/
function Silence(duration){
this.duration = isNaN(duration) || duration === null ? this.duration : duration;
this.elem = document.createElement('audio');
var sr = 11025,
l = ~~(this.duration * sr),
data =
'WAVE' + // RIFF ID
'fmt ' + // Chunk ID
dWord(16) + // Chunk size
sWord(1) + // Format
sWord(1) + // Channels
dWord(sr) + // Sample rate
dWord(sr) + // Byte rate (8 bit audio)
sWord(1) + // Block align (8 bit audio)
sWord(8) + // Bits per sample
'data' + // Chunk ID
dWord(l) + // Chunk size
Array(l+1).join('\x7F') ; // Data
data =
'RIFF' + // Group ID
dWord(data.length) + // File Length
data;
this.url = new DynUrl(data, 'audio/wav');
this.elem.src = this.url;
}
Silence.prototype = {
elem: null,
url: null,
duration: 5,
/* Call this when discarding the audio to avoid memory leaks */
destroy: function(){
this.url.revoke();
}
};
g.DynUrl = DynUrl;
g.Silence = Silence;
}(this));
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