fix copy tag in reduce-bitrate by id3lib app

reduce_bitrate.sh

@@ -52,6 +52,14 @@ get_bitrate_kbps() {
     return 1
 }
 
+restore_metadata() {
+    local source_file="$1"
+    local target_file="$2"
+
+    id3cp "$source_file" "$target_file" >/dev/null 2>&1
+    return $?
+}
+
 process_file() {
     local file="$1"
     local current_bitrate
@@ -85,8 +93,18 @@ process_file() {
     temp_file="${file%.mp3}_temp_$$.mp3"
     if ffmpeg -nostdin -y -i "$file" -b:a "${TARGET_BITRATE}" -id3v2_version 3 "$temp_file" > /dev/null 2>&1; then
         mv "$temp_file" "$file"
-        log_success "Converted: ${file} (${current_bitrate} kbps ➜ ${TARGET_BITRATE}) ✅"
-        ((converted_count++))
+
+        # Restore all metadata from backup file
+        if restore_metadata "$backup_file" "$file"; then
+            log_success "Converted: ${file} (${current_bitrate} kbps ➜ ${TARGET_BITRATE}) ✅"
+            ((converted_count++))
+        else
+            log_error "Metadata restoration failed: ${file}"
+            # Revert to backup since metadata restoration failed
+            cp "$backup_file" "$file"
+            log_warn "Reverted to backup (conversion skipped due to metadata error)"
+            ((error_count++))
+        fi
     else
         rm -f "$temp_file"
         log_error "ffmpeg failed: ${file}"
@@ -117,6 +135,11 @@ if ! command -v ffprobe >/dev/null 2>&1 || ! command -v ffmpeg >/dev/null 2>&1;
     exit 1
 fi
 
+if ! command -v id3cp >/dev/null 2>&1; then
+    log_error "id3cp not found. Please install id3lib (Arch: id3lib, Debian/Ubuntu: libid3-tools)."
+    exit 1
+fi
+
 if [ ! -d "$ROOT_DIR" ]; then
     log_error "Directory not found: ${ROOT_DIR}"
     exit 1