diff --git a/modules/yt-dlp.nix b/modules/yt-dlp.nix
index 2e42ee6..fc1458b 100644
--- a/modules/yt-dlp.nix
+++ b/modules/yt-dlp.nix
@@ -43,6 +43,42 @@ in
       source = ../config/yt-dlp/cookies-bilibili.txt;
     };
 
+    # Audio normalization post-processing script
+    home.file.".config/yt-dlp/normalize-audio.sh" = {
+      text = ''
+        # Post-processing script to add normalized audio track
+        # Usage: normalize-audio.sh <video-file>
+
+        file="$1"
+
+        # Only process MP4 files
+        if [[ "$file" != *.mp4 ]]; then
+          exit 0
+        fi
+
+        echo "Adding normalized audio track..."
+        temp="''${file}.temp.mp4"
+
+        # Add normalized audio track alongside original
+        # Track 0: Original audio
+        # Track 1: Normalized audio (lower volume, -27 LUFS) with metadata name
+        if ffmpeg -loglevel error -i "$file" \
+          -map 0:v -c:v copy \
+          -map 0:a:0 -c:a:0 copy \
+          -map 0:a:0 -filter:a:1 "loudnorm=I=-27:TP=-2:LRA=7" -c:a:1 aac -b:a:1 128k \
+          -metadata:s:a:1 title="dlv-normalized" \
+          -y "$temp"; then
+          mv "$temp" "$file"
+          echo "✓ Normalized audio track added"
+        else
+          echo "✗ Failed to add normalized audio track"
+          rm -f "$temp"
+          exit 1
+        fi
+      '';
+      executable = true;
+    };
+
     # Create yt-dlp configuration file
     home.file.".config/yt-dlp/config".text = ''
       # Quality settings
@@ -71,6 +107,9 @@ in
       # SponsorBlock for YouTube
       --sponsorblock-mark all
 
+      # Audio normalization post-processing
+      --exec after_move:~/.config/yt-dlp/normalize-audio.sh
+
       # User agent
       --user-agent "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36"
     '';
@@ -345,6 +384,68 @@ in
       
       # Alias for backward compatibility
       alias dlv-clear-archive='dl-clear-archive'
+
+      # Function to retrospectively normalize audio for all videos in a directory
+      dlv-normalize-dir() {
+        local target_dir="''${1:-.}"
+
+        # Normalize path and expand tilde
+        target_dir="''${target_dir/#\~/$HOME}"
+
+        if [[ ! -d "$target_dir" ]]; then
+          echo "✗ Error: Directory not found: $target_dir"
+          return 1
+        fi
+
+        echo "Scanning for MP4 files in: $target_dir"
+
+        # Find all MP4 files
+        local files=()
+        while IFS= read -r -d $'\0' file; do
+          files+=("$file")
+        done < <(find "$target_dir" -type f -name "*.mp4" -print0)
+
+        if [[ ''${#files[@]} -eq 0 ]]; then
+          echo "No MP4 files found in directory"
+          return 0
+        fi
+
+        echo "Found ''${#files[@]} MP4 file(s)"
+        echo ""
+
+        local processed=0
+        local skipped=0
+        local failed=0
+        local current=0
+
+        for file in "''${files[@]}"; do
+          ((current++))
+          echo "[$current/''${#files[@]}] Processing: $(basename "$file")"
+
+          # Check if file already has multiple audio tracks (already processed)
+          local audio_count=$(ffprobe -v error -select_streams a -show_entries stream=index -of csv=p=0 "$file" 2>/dev/null | wc -l)
+
+          if [[ $audio_count -ge 2 ]]; then
+            echo "  ⊙ Skipped (already has $audio_count audio tracks)"
+            ((skipped++))
+          else
+            # Run the normalization script
+            if ~/.config/yt-dlp/normalize-audio.sh "$file"; then
+              ((processed++))
+            else
+              ((failed++))
+            fi
+          fi
+          echo ""
+        done
+
+        echo "════════════════════════════════════════"
+        echo "Summary:"
+        echo "  ✓ Processed: $processed"
+        echo "  ⊙ Skipped:   $skipped"
+        [[ $failed -gt 0 ]] && echo "  ✗ Failed:    $failed"
+        echo "════════════════════════════════════════"
+      }
     '';
   };
 }