Methods for creating an audio tag filled with a specified time of silence.

silence.js

(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));