fix: ignore dtx streams (#35)

Author: desher

src/detectors/FrozenVideoTrackDetector.ts

@@ -1,3 +1,4 @@
+import { isDtxLikeBehavior } from '../helpers/streams';
 import {
   IssueDetectorResult,
   IssueReason,
@@ -71,6 +72,12 @@ class FrozenVideoTrackDetector extends BaseIssueDetector {
           return undefined;
         }
 
+        const isDtx = isDtxLikeBehavior(videoStream.ssrc, allLastProcessedStats);
+        if (isDtx) {
+          // DTX-like behavior detected, ignoring freezes check
+          return undefined;
+        }
+
         const deltaFreezeCount = videoStream.freezeCount - (prevStat.freezeCount ?? 0);
         const deltaFreezesTimeMs = (videoStream.totalFreezesDuration - (prevStat.totalFreezesDuration ?? 0)) * 1000;
         const avgFreezeDurationMs = deltaFreezeCount > 0 ? deltaFreezesTimeMs / deltaFreezeCount : 0;

src/detectors/VideoDecoderIssueDetector.ts

@@ -1,4 +1,5 @@
 import { calculateVolatility } from '../helpers/calc';
+import { isDtxLikeBehavior } from '../helpers/streams';
 import {
   IssueDetectorResult,
   IssueReason,
@@ -84,6 +85,12 @@ class VideoDecoderIssueDetector extends BaseIssueDetector {
           return undefined;
         }
 
+        const isDtx = isDtxLikeBehavior(incomeVideoStream.ssrc, allProcessedStats);
+        if (isDtx) {
+          // DTX-like behavior detected, ignoring FPS volatility check
+          return undefined;
+        }
+
         const volatility = calculateVolatility(allFps);
 
         if (volatility > this.#volatilityThreshold) {

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

@@ -0,0 +1,42 @@
+import { WebRTCStatsParsedWithNetworkScores } from '../types';
+import { calculateStandardDeviation } from './calc';
+
+export const isDtxLikeBehavior = (
+  ssrc: number,
+  allProcessedStats: WebRTCStatsParsedWithNetworkScores[],
+  stdDevThreshold = 30,
+): boolean => {
+  const frameIntervals: number[] = [];
+  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,
+    );
+
+    if (!videoStreamStats || !previousVideoStreamStats) {
+      continue;
+    }
+
+    const deltaTime = videoStreamStats.timestamp - previousVideoStreamStats.timestamp;
+    const deltaFrames = videoStreamStats.framesDecoded - previousVideoStreamStats.framesDecoded;
+
+    if (deltaFrames > 0) {
+      const frameInterval = deltaTime / deltaFrames; // Average time per frame
+      frameIntervals.push(frameInterval);
+    }
+  }
+
+  if (frameIntervals.length <= 1) {
+    return false;
+  }
+
+  const stdDev = calculateStandardDeviation(frameIntervals);
+  return stdDev > stdDevThreshold;
+};