Tighten MPEG classification and reduce false positives

src/AudioAnalyzer.cpp

@@ -529,9 +529,12 @@ AudioAnalysisReport AudioAnalyzer::analyzeFile(const QString &path) const {
     const double genuineRatio = static_cast<double>(report.genuineWindows) / report.informativeWindows;
 
     const bool hasStrongCdBoundary = report.cutoffKhz > 20.5 && report.rolloffKhz > 18.5 &&
-        report.spectralFlatness > 0.09 && report.suspectRatio <= 0.20;
+        report.spectralFlatness > 0.06 && report.suspectRatio <= 0.20;
     const bool hasCdTopBand = report.veryHighBandRatio > 0.0000005 && report.spectralFlatness > 0.09;
     const bool hasLossyFlatness = report.spectralFlatness < 0.075;
+    const bool hasLossyBoundary = report.cutoffKhz < 19.5 || report.rolloffKhz < 17.5;
+    const bool hasStrongLowpassSignature = hasLossyFlatness && hasLossyBoundary;
+    const bool hasSuspectEvidence = report.suspectWindows >= 2 && report.suspectRatio >= 0.45;
     const bool hasAacLikeLowpass = report.veryHighBandRatio <= 0.0000005 && report.spectralFlatness < 0.19 &&
         report.suspectRatio >= 0.55 && report.suspectWindows >= 2;
 
@@ -549,7 +552,8 @@ AudioAnalysisReport AudioAnalyzer::analyzeFile(const QString &path) const {
         report.conclusion = QString("CDDA %1").arg(QString::number(confidence) + "%");
         report.accuracy = QString::number(confidence) + "%";
         report.confidence = confidence;
-    } else if (hasLossyFlatness || hasAacLikeLowpass || (report.suspectRatio >= 0.72 && report.suspectWindows >= 4)) {
+    } else if (hasAacLikeLowpass || hasStrongLowpassSignature ||
+        (hasSuspectEvidence && (hasLossyFlatness || hasLossyBoundary || report.suspectRatio >= 0.72))) {
         const int confidence = std::clamp(static_cast<int>(std::round(55.0 + report.suspectRatio * 45.0)), 55, 100);
         report.conclusion = QString("MPEG %1").arg(QString::number(confidence) + "%");
         report.accuracy = QString::number(confidence) + "%";