Code to generate SVG waveforms from mp3 files.

gistfile1.js

var lame = require('lame');
var through = require('through2');
var fs = require('fs');
var d3 = require('d3');

var file = fs.createReadStream('source.mp3');
var frames = [], frameBuffer = [];
var format;

var decoder = new lame.Decoder();

decoder.on('format', function (form) {
	format = form;
	switch (format.bitDepth) {
	case 8:
		format.readName = 'readInt8';
		format.increment = 1;
		break;
	case 16:
		format.readName = 'readInt16LE';
		format.increment = 2;
		break;
	case 32:
		format.readName = 'readInt32LE';
		format.increment = 4;
		break;
	default:
		console.error('Unsupported bitdepth: ', format.bitDepth);
		process.exit();
	}
	

	decoder.pipe(through(frameReader, process));
});

var max = 0;

function frameReader (chunk, enc, next) {
	var i = 0, c = chunk.length;
	var channel;
	var frame;
	while (i < c) {
		frame = [];
		for (channel=0;channel < format.channels;channel++) {
			frame[channel] = chunk[format.readName](i);
			i += format.increment;
			max = Math.max(max, Math.abs(frame[channel]));
		}
		frames.push(frame);
	}

	next();
}

file.pipe(decoder);

function reduce (frames) {
	var result = [], set, channel, sum, avg,
		offset = 0,
		len = frames.length,
		sampleSize = format.sampleRate / 100;

	while (offset < len) {
		set = frames.slice(offset, offset + sampleSize);
		offset += sampleSize;

		if (set.length) {
			sum = [];
			avg = [];
			for (channel=0;channel < format.channels;channel++) {
				sum[channel] = set.reduce(function(a, b) { return a + b[channel]; }, 0);
				avg[channel] = Math.round(sum[channel] / set.length);
			}

			result.push(avg);
		}
	}

	return result;
}

function process () {
	var reduction = reduce(frames);
	var height = 600;

	var y = d3.scale.linear()
		.domain([-max, max])
		.range([-height, height]);

	var svg = d3.select('body').append('svg')
		.attr('width', reduction.length)
		.attr('height', height)
		.append('g')
			.attr("transform", "translate(0," + (height / 2) + ")");

	var line = d3.svg.line()
		.x(function(d, i) { return i; })
		.y(function(d) { return y(d[0]); });

	svg.append('path')
		.datum(reduction)
		.style("fill:none;stroke:black;stroke-width: 0.5px;")
		.attr('d', line);

	var html = d3.select('body').node().innerHTML;

	fs.writeFileSync('waveform.html', html);
}