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- var probe = require("../lib/probe.js"),
- d3 = require("d3"),
- pcmStream = require("../lib/pcm.js");
-
- function getWaveform(filename, options, cb) {
-
- var stream = pcmStream(filename, {
- channels: options.channels
- }),
- samples = [];
-
- stream.on("data",function(sample, channel){
-
- // Average multiple channels
- if (channel > 0) {
- samples[samples.length - 1] = ((samples[samples.length - 1] * channel) + sample) / (channel + 1);
- } else {
- samples.push(sample);
- }
-
- });
-
- stream.on("error", cb);
-
- stream.on("end", function(output){
- var processed = processSamples(samples, options.numFrames, options.samplesPerFrame);
- return cb(null, processed);
- });
-
- }
-
- function processSamples(samples, numFrames, samplesPerFrame) {
-
- // TODO spread out slop across frames
- var perFrame = Math.floor(samples.length / numFrames),
- perPoint = Math.floor(perFrame / samplesPerFrame),
- range = d3.range(samplesPerFrame),
- maxFrame,
- maxMedian = max = 0;
-
- var unadjusted = d3.range(numFrames).map(function(frame){
-
- var frameSamples = samples.slice(frame * perFrame, (frame + 1) * perFrame),
- points = range.map(function(point){
-
- var pointSamples = frameSamples.slice(point * perPoint, (point + 1) * perPoint);
-
- var rms = Math.sqrt(d3.sum(pointSamples.map(function(d){
- return d * d;
- })) / perPoint);
-
- if (rms > max) {
- max = rms;
- }
-
- // Min value, max value, and midpoint value
- return [-rms, rms, pointSamples[Math.floor(pointSamples.length / 2)]];
-
- }),
- median = d3.median(points.map(function(point){
- return point[1];
- }));
-
- if (median > maxMedian) {
- maxMedian = median;
- maxFrame = frame;
- }
-
- return points;
-
- });
-
- // Scale up to -1 / 1
- var adjustment = 1 / max;
-
- var adjusted = unadjusted.map(function(frame){
- return frame.map(function(point){
- return point.map(function(p){ return adjustment * p; });
- });
- });
-
- // Make first and last frame peaky
- adjusted[0] = adjusted[numFrames - 1] = adjusted[maxFrame];
-
- return adjusted;
-
- }
-
- module.exports = getWaveform;
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