Add audio quality check script with delta ratio analysis

This script calculates the Maximum delta / Mean delta ratio to detect
clicks in FLAC files. A ratio > 10 indicates audio discontinuities caused
by buffer underruns during encoding.

Usage: ./check_audio_quality.sh [cache_directory]

The script helps verify that the PCM buffer fix (256 instead of 8) has
eliminated the clicks.

check_audio_quality.sh

@@ -0,0 +1,90 @@
+#!/bin/bash
+# Script pour vérifier la qualité audio (détection de clics via le ratio delta)
+
+CACHE_DIR="${1:-/tmp/pmomusic_test/audio_cache}"
+THRESHOLD=10.0  # Ratio Maximum delta / Mean delta acceptable
+
+if [ ! -d "$CACHE_DIR" ]; then
+    echo "Error: Cache directory not found: $CACHE_DIR"
+    exit 1
+fi
+
+echo "=== Audio Quality Check ==="
+echo "Scanning: $CACHE_DIR"
+echo "Threshold: Maximum/Mean delta ratio < $THRESHOLD"
+echo ""
+
+# Vérifier que sox est installé
+if ! command -v sox &> /dev/null; then
+    echo "Error: sox is not installed. Install it with: sudo apt install sox"
+    exit 1
+fi
+
+count=0
+suspicious=0
+good=0
+
+for file in "$CACHE_DIR"/*.orig.flac; do
+    if [ ! -f "$file" ]; then
+        echo "No FLAC files found in $CACHE_DIR"
+        exit 0
+    fi
+
+    filename=$(basename "$file")
+
+    # Obtenir les stats delta
+    stats=$(sox "$file" -n stat 2>&1)
+
+    max_delta=$(echo "$stats" | grep "Maximum delta" | awk '{print $3}')
+    mean_delta=$(echo "$stats" | grep "Mean    delta" | awk '{print $3}')
+
+    if [ -z "$max_delta" ] || [ -z "$mean_delta" ]; then
+        echo "❌ $filename - Cannot parse stats"
+        suspicious=$((suspicious + 1))
+        count=$((count + 1))
+        continue
+    fi
+
+    # Éviter division par zéro
+    if (( $(echo "$mean_delta == 0" | bc -l) )); then
+        echo "❌ $filename - Invalid mean delta (0)"
+        suspicious=$((suspicious + 1))
+        count=$((count + 1))
+        continue
+    fi
+
+    # Calculer le ratio
+    ratio=$(echo "scale=2; $max_delta / $mean_delta" | bc -l)
+
+    # Comparer au seuil
+    is_bad=$(echo "$ratio > $THRESHOLD" | bc -l)
+
+    if [ "$is_bad" = "1" ]; then
+        echo "⚠️  CLICKS DETECTED: $filename"
+        echo "    Max delta: $max_delta, Mean delta: $mean_delta, Ratio: ${ratio}x (threshold: ${THRESHOLD}x)"
+        suspicious=$((suspicious + 1))
+    else
+        echo "✓  OK: $filename (ratio: ${ratio}x)"
+        good=$((good + 1))
+    fi
+
+    count=$((count + 1))
+done
+
+echo ""
+echo "=== Summary ==="
+echo "Total files scanned: $count"
+echo "✓ Good quality: $good"
+echo "⚠️  Clicks detected: $suspicious"
+
+if [ $suspicious -gt 0 ]; then
+    echo ""
+    echo "⚠️  Warning: $suspicious file(s) have clicks."
+    echo "These files were likely encoded with the old buffer size (8)."
+    echo "Delete the cache and re-download to fix: rm -rf $CACHE_DIR/*.flac"
+    exit 1
+fi
+
+echo ""
+echo "✓ All files are good quality!"
+exit 0