Optimize Memory and Performance in waveform.js

audiogram/waveform.js

@@ -4,45 +4,45 @@ var probe = require("../lib/probe.js"),
 
 function getWaveform(filename, options, cb) {
 
+  // Pre-allocate samples array if possible
+  let expectedSize = 100000;  // Replace with an accurate estimate if possible
+  let samples = new Float64Array(expectedSize);
+  let sampleCount = 0;
+
   var stream = pcmStream(filename, {
-        channels: options.channels
-      }),
-      samples = [];
+    channels: options.channels
+  });
 
-  stream.on("data",function(sample, channel){
+  stream.on("data", function(sample, channel){
+    let lastSampleIndex = sampleCount - 1;
+    let nextChannel = channel + 1;
 
-    // Average multiple channels
     if (channel > 0) {
-      samples[samples.length - 1] = ((samples[samples.length - 1] * channel) + sample) / (channel + 1);
+      samples[lastSampleIndex] = ((samples[lastSampleIndex] * channel) + sample) / nextChannel;
     } else {
-      samples.push(sample);
+      samples[sampleCount] = sample;
+      sampleCount++;
     }
-
   });
 
   stream.on("error", cb);
 
-  stream.on("end", function(output){
-    var processed = processSamples(samples, options.numFrames, options.samplesPerFrame);
+  stream.on("end", function(){
+    // Trim the pre-allocated array to the actual size
+    let trimmedSamples = samples.subarray(0, sampleCount);
+    var processed = processSamples(trimmedSamples, 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,
       maxRms = maxMid = 0;
 
   var unadjusted = d3.range(numFrames).map(function(frame){
-
     var frameSamples = samples.slice(frame * perFrame, (frame + 1) * perFrame),
-        points = range.map(function(point){
-
+        points = d3.range(samplesPerFrame).map(function(point){
           var pointSamples = frameSamples.slice(point * perPoint, (point + 1) * perPoint),
               midpoint = pointSamples[Math.floor(pointSamples.length / 2)];
 
@@ -52,20 +52,16 @@ function processSamples(samples, numFrames, samplesPerFrame) {
 
           if (rms > maxRms) {
             maxRms = rms;
-            maxFrame = frame;
           }
 
           if (Math.abs(midpoint) > maxMid) {
             maxMid = Math.abs(midpoint);
           }
 
-          // Min value, max value, and midpoint value
           return [rms, midpoint];
-
         });
 
     return points;
-
   });
 
   var adjusted = unadjusted.map(function(frame){
@@ -78,10 +74,19 @@ function processSamples(samples, numFrames, samplesPerFrame) {
   });
 
   // Make first and last frame peaky
-  adjusted[0] = adjusted[numFrames - 1] = adjusted[maxFrame];
+  // adjusted[0] = adjusted[numFrames - 1] = adjusted[d3.maxIndex(unadjusted, d => d[0])];
+  let maxIndex = 0;
+  let maxValue = -Infinity;
+  for(let i = 0; i < unadjusted.length; i++) {
+      let currMax = Math.max(...unadjusted[i].map(d => d[0]));
+      if(currMax > maxValue) {
+          maxValue = currMax;
+          maxIndex = i;
+      }
+  }
+  adjusted[0] = adjusted[numFrames - 1] = adjusted[maxIndex];
 
   return adjusted;
-
 }
 
 module.exports = getWaveform;