fix: review improvements

Author: desher

src/helpers/calc.ts

@@ -1,5 +1,14 @@
 export const calculateMean = (values: number[]) => values.reduce((acc, val) => acc + val, 0) / values.length;
 
+export const calculateVariance = (mean: number, values: number[]) => values
+  .reduce((sum, val) => sum + (val - mean) ** 2, 0) / values.length;
+
+export const calculateStandardDeviation = (values: number[]) => {
+  const mean = calculateMean(values);
+  const variance = calculateVariance(mean, values);
+  return Math.sqrt(variance);
+};
+
 export const calculateVolatility = (values: number[]) => {
   if (values.length === 0) {
     throw new Error('Cannot calculate volatility for empty array');

src/helpers/streams.ts

@@ -1,16 +1,21 @@
 import { WebRTCStatsParsedWithNetworkScores } from '../types';
+import { calculateStandardDeviation } from './calc';
 
 export const isDtxLikeBehavior = (
   ssrc: number,
   allProcessedStats: WebRTCStatsParsedWithNetworkScores[],
   stdDevThreshold = 30,
 ): boolean => {
   const frameIntervals: number[] = [];
-  for (let i = 0; i < allProcessedStats.length - 1; i += 1) {
-    const videoStreamStats = allProcessedStats[i].video.inbound.find(
+  for (let i = 1; i < allProcessedStats.length - 1; i += 1) {
+    const videoStreamStats = allProcessedStats[i]?.video?.inbound.find(
       (stream) => stream.ssrc === ssrc,
     );
 
+    if (!videoStreamStats) {
+      continue;
+    }
+
     const previousVideoStreamStats = allProcessedStats[i - 1]?.video?.inbound?.find(
       (stream) => stream.ssrc === ssrc,
     );
@@ -32,9 +37,6 @@ export const isDtxLikeBehavior = (
     return false;
   }
 
-  const mean = frameIntervals.reduce((a, b) => a + b, 0) / frameIntervals.length;
-  const variance = frameIntervals
-    .reduce((sum, val) => sum + (val - mean) ** 2, 0) / frameIntervals.length;
-  const stdDev = Math.sqrt(variance);
+  const stdDev = calculateStandardDeviation(frameIntervals);
   return stdDev > stdDevThreshold;
 };