function calcBitrate(){
	var targetSize;
	/* time */
	var t;
	/* bitrate */
	var b;
	/* decimal places */
	var dec = 1;

	if (document.bitrate.length_h.value == "HH" || document.bitrate.length_h.value == "") document.bitrate.length_h.value = 0;
	if (document.bitrate.length_m.value == "MM" || document.bitrate.length_m.value == "") document.bitrate.length_m.value = 0;
	if (document.bitrate.length_s.value == "SS" || document.bitrate.length_s.value == "") document.bitrate.length_s.value = 0;
	var t = ((document.bitrate.length_h.value * 3600) + (document.bitrate.length_m.value * 60) + eval(document.bitrate.length_s.value));
	
	if (document.bitrate.size_value.value == "") document.bitrate.size_value.value = 0;
	var targetSize = (document.bitrate.size_value.value * document.bitrate.size_unit.value);
	
	var b = (targetSize / (t / 8));
	
	if (b < 1000) document.bitrate.bitrate_out.value = roundNumber(b, 0) + " bps";
	else if (b >= 1000 && b < 1000000) document.bitrate.bitrate_out.value = roundNumber((b / 1000), dec) + " kbps";
	else if (b >= 1000000 && b < 1000000000) document.bitrate.bitrate_out.value = roundNumber((b / 1000000), dec) + " mbps";
	else if (b >= 1000000000) document.bitrate.bitrate_out.value = roundNumber((b / 1000000000), dec) + " gbps";
	else document.bitrate.bitrate_out.value = "error";
}
function roundNumber(num, dec) {
	var result = Math.round( Math.round( num * Math.pow( 10, dec + 1 ) ) / Math.pow( 10, 1 ) ) / Math.pow(10,dec);
	return result;
}