feat: add FLAC/ALAC bidirectional lossless conversion support

- Add _convertToAlac() and _convertToFlac() in ffmpeg_service with
  single-pass FFmpeg encoding, metadata tags, and cover art embedding
- Wire lossless formats (ALAC, FLAC) into single-track convert sheet
  with dynamic format list based on source format, hidden bitrate for
  lossless targets, and lossless hint text
- Add lossless conversion to batch convert UI in downloaded_album,
  local_album, and queue_tab screens with lossy-source filtering
- Fix M4A quality probe in Go backend: increase audio sample entry
  buffer from 24 to 32 bytes, read sample rate from correct offset
  (bytes 28-29) and bit depth from samplesize field (bytes 22-23)
- Add l10n keys for lossless confirm dialogs and hints (en, id)

go_backend/metadata.go

@@ -743,15 +743,28 @@ func GetM4AQuality(filePath string) (AudioQuality, error) {
 		return AudioQuality{}, err
 	}
 
-	buf := make([]byte, 24)
+	buf := make([]byte, 32)
 	if _, err := f.ReadAt(buf, sampleOffset); err != nil {
 		return AudioQuality{}, fmt.Errorf("failed to read audio sample entry: %w", err)
 	}
 
-	sampleRate := int(buf[22])<<8 | int(buf[23])
-	bitDepth := 16
-	if atomType == "alac" {
-		bitDepth = 24
+	// AudioSampleEntry layout from the box type field:
+	//   [0:4]   type ("mp4a"/"alac")
+	//   [4:10]  SampleEntry.reserved
+	//   [10:12] data_reference_index
+	//   [12:20] reserved[8]
+	//   [20:22] channelcount
+	//   [22:24] samplesize (bit depth)
+	//   [24:26] pre_defined
+	//   [26:28] reserved
+	//   [28:32] samplerate (16.16 fixed-point)
+	sampleRate := int(buf[28])<<8 | int(buf[29])
+	bitDepth := int(buf[22])<<8 | int(buf[23])
+	if bitDepth <= 0 {
+		bitDepth = 16
+		if atomType == "alac" {
+			bitDepth = 24
+		}
 	}
 
 	return AudioQuality{BitDepth: bitDepth, SampleRate: sampleRate}, nil
@@ -874,7 +887,7 @@ func findAudioSampleEntry(f *os.File, start, end, fileSize int64) (int64, string
 
 		if bestIdx >= 0 {
 			absolute := readPos - int64(len(tail)) + int64(bestIdx)
-			if absolute+24 > fileSize {
+			if absolute+32 > fileSize {
 				return 0, "", fmt.Errorf("audio info not found in M4A file")
 			}
 			return absolute, bestType, nil

lib/l10n/app_localizations.dart

@@ -3883,7 +3883,7 @@ abstract class AppLocalizations {
   /// Subtitle for convert format menu item
   ///
   /// In en, this message translates to:
-  /// **'Convert to MP3 or Opus'**
+  /// **'Convert to MP3, Opus, ALAC, or FLAC'**
   String get trackConvertFormatSubtitle;
 
   /// Title of convert bottom sheet
@@ -3920,6 +3920,21 @@ abstract class AppLocalizations {
     String bitrate,
   );
 
+  /// Confirmation dialog message for lossless-to-lossless conversion
+  ///
+  /// In en, this message translates to:
+  /// **'Convert from {sourceFormat} to {targetFormat}? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.'**
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  );
+
+  /// Hint shown when converting between lossless formats
+  ///
+  /// In en, this message translates to:
+  /// **'Lossless conversion — no quality loss'**
+  String get trackConvertLosslessHint;
+
   /// Snackbar while converting
   ///
   /// In en, this message translates to:
@@ -4290,6 +4305,12 @@ abstract class AppLocalizations {
     String bitrate,
   );
 
+  /// Confirmation dialog message for lossless batch conversion
+  ///
+  /// In en, this message translates to:
+  /// **'Convert {count} {count, plural, =1{track} other{tracks}} to {format}? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.'**
+  String selectionBatchConvertConfirmMessageLossless(int count, String format);
+
   /// Snackbar during batch conversion progress
   ///
   /// In en, this message translates to:

lib/l10n/app_localizations_de.dart

@@ -2226,6 +2226,18 @@ class AppLocalizationsDe extends AppLocalizations {
     return 'Konvertieren von $sourceFormat in $targetFormat bei $bitrate?\n\nDie Originaldatei wird nach der Konvertierung gelöscht.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Convert from $sourceFormat to $targetFormat? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Lossless conversion — no quality loss';
+
   @override
   String get trackConvertConverting => 'Konvertiere Audio...';
 
@@ -2480,6 +2492,17 @@ class AppLocalizationsDe extends AppLocalizations {
     return 'Konvertiere $count $format $_temp0 zu $bitrate?\n\nOriginaldateien werden nach der Konvertierung gelöscht.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Konvertiere $current von $total...';

lib/l10n/app_localizations_en.dart

@@ -2176,7 +2176,8 @@ class AppLocalizationsEn extends AppLocalizations {
   String get trackConvertFormat => 'Convert Format';
 
   @override
-  String get trackConvertFormatSubtitle => 'Convert to MP3 or Opus';
+  String get trackConvertFormatSubtitle =>
+      'Convert to MP3, Opus, ALAC, or FLAC';
 
   @override
   String get trackConvertTitle => 'Convert Audio';
@@ -2199,6 +2200,18 @@ class AppLocalizationsEn extends AppLocalizations {
     return 'Convert from $sourceFormat to $targetFormat at $bitrate?\n\nThe original file will be deleted after conversion.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Convert from $sourceFormat to $targetFormat? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Lossless conversion — no quality loss';
+
   @override
   String get trackConvertConverting => 'Converting audio...';
 
@@ -2452,6 +2465,17 @@ class AppLocalizationsEn extends AppLocalizations {
     return 'Convert $count $_temp0 to $format at $bitrate?\n\nOriginal files will be deleted after conversion.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Converting $current of $total...';

lib/l10n/app_localizations_es.dart

@@ -2176,7 +2176,8 @@ class AppLocalizationsEs extends AppLocalizations {
   String get trackConvertFormat => 'Convert Format';
 
   @override
-  String get trackConvertFormatSubtitle => 'Convert to MP3 or Opus';
+  String get trackConvertFormatSubtitle =>
+      'Convert to MP3, Opus, ALAC, or FLAC';
 
   @override
   String get trackConvertTitle => 'Convert Audio';
@@ -2199,6 +2200,18 @@ class AppLocalizationsEs extends AppLocalizations {
     return 'Convert from $sourceFormat to $targetFormat at $bitrate?\n\nThe original file will be deleted after conversion.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Convert from $sourceFormat to $targetFormat? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Lossless conversion — no quality loss';
+
   @override
   String get trackConvertConverting => 'Converting audio...';
 
@@ -2452,6 +2465,17 @@ class AppLocalizationsEs extends AppLocalizations {
     return 'Convert $count $_temp0 to $format at $bitrate?\n\nOriginal files will be deleted after conversion.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Converting $current of $total...';

lib/l10n/app_localizations_fr.dart

@@ -2201,6 +2201,18 @@ class AppLocalizationsFr extends AppLocalizations {
     return 'Convert from $sourceFormat to $targetFormat at $bitrate?\n\nThe original file will be deleted after conversion.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Convert from $sourceFormat to $targetFormat? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Lossless conversion — no quality loss';
+
   @override
   String get trackConvertConverting => 'Converting audio...';
 
@@ -2454,6 +2466,17 @@ class AppLocalizationsFr extends AppLocalizations {
     return 'Convert $count $_temp0 to $format at $bitrate?\n\nOriginal files will be deleted after conversion.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Converting $current of $total...';

lib/l10n/app_localizations_hi.dart

@@ -2199,6 +2199,18 @@ class AppLocalizationsHi extends AppLocalizations {
     return 'Convert from $sourceFormat to $targetFormat at $bitrate?\n\nThe original file will be deleted after conversion.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Convert from $sourceFormat to $targetFormat? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Lossless conversion — no quality loss';
+
   @override
   String get trackConvertConverting => 'Converting audio...';
 
@@ -2452,6 +2464,17 @@ class AppLocalizationsHi extends AppLocalizations {
     return 'Convert $count $_temp0 to $format at $bitrate?\n\nOriginal files will be deleted after conversion.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Converting $current of $total...';

lib/l10n/app_localizations_id.dart

@@ -2183,7 +2183,8 @@ class AppLocalizationsId extends AppLocalizations {
   String get trackConvertFormat => 'Convert Format';
 
   @override
-  String get trackConvertFormatSubtitle => 'Convert to MP3 or Opus';
+  String get trackConvertFormatSubtitle =>
+      'Konversi ke MP3, Opus, ALAC, atau FLAC';
 
   @override
   String get trackConvertTitle => 'Convert Audio';
@@ -2206,6 +2207,18 @@ class AppLocalizationsId extends AppLocalizations {
     return 'Convert from $sourceFormat to $targetFormat at $bitrate?\n\nThe original file will be deleted after conversion.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Konversi dari $sourceFormat ke $targetFormat? (Lossless — tanpa kehilangan kualitas)\n\nFile asli akan dihapus setelah konversi.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Konversi lossless — tanpa kehilangan kualitas';
+
   @override
   String get trackConvertConverting => 'Converting audio...';
 
@@ -2459,6 +2472,17 @@ class AppLocalizationsId extends AppLocalizations {
     return 'Convert $count $_temp0 to $format at $bitrate?\n\nOriginal files will be deleted after conversion.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Converting $current of $total...';

lib/l10n/app_localizations_ja.dart

@@ -2186,6 +2186,18 @@ class AppLocalizationsJa extends AppLocalizations {
     return 'Convert from $sourceFormat to $targetFormat at $bitrate?\n\nThe original file will be deleted after conversion.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Convert from $sourceFormat to $targetFormat? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Lossless conversion — no quality loss';
+
   @override
   String get trackConvertConverting => 'オーディオを変換中...';
 
@@ -2439,6 +2451,17 @@ class AppLocalizationsJa extends AppLocalizations {
     return 'Convert $count $_temp0 to $format at $bitrate?\n\nOriginal files will be deleted after conversion.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Converting $current of $total...';

lib/l10n/app_localizations_ko.dart

@@ -2179,6 +2179,18 @@ class AppLocalizationsKo extends AppLocalizations {
     return 'Convert from $sourceFormat to $targetFormat at $bitrate?\n\nThe original file will be deleted after conversion.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Convert from $sourceFormat to $targetFormat? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Lossless conversion — no quality loss';
+
   @override
   String get trackConvertConverting => 'Converting audio...';
 
@@ -2432,6 +2444,17 @@ class AppLocalizationsKo extends AppLocalizations {
     return 'Convert $count $_temp0 to $format at $bitrate?\n\nOriginal files will be deleted after conversion.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Converting $current of $total...';

lib/l10n/app_localizations_nl.dart

@@ -2199,6 +2199,18 @@ class AppLocalizationsNl extends AppLocalizations {
     return 'Convert from $sourceFormat to $targetFormat at $bitrate?\n\nThe original file will be deleted after conversion.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Convert from $sourceFormat to $targetFormat? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Lossless conversion — no quality loss';
+
   @override
   String get trackConvertConverting => 'Converting audio...';
 
@@ -2452,6 +2464,17 @@ class AppLocalizationsNl extends AppLocalizations {
     return 'Convert $count $_temp0 to $format at $bitrate?\n\nOriginal files will be deleted after conversion.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Converting $current of $total...';

lib/l10n/app_localizations_pt.dart

@@ -2176,7 +2176,8 @@ class AppLocalizationsPt extends AppLocalizations {
   String get trackConvertFormat => 'Convert Format';
 
   @override
-  String get trackConvertFormatSubtitle => 'Convert to MP3 or Opus';
+  String get trackConvertFormatSubtitle =>
+      'Convert to MP3, Opus, ALAC, or FLAC';
 
   @override
   String get trackConvertTitle => 'Convert Audio';
@@ -2199,6 +2200,18 @@ class AppLocalizationsPt extends AppLocalizations {
     return 'Convert from $sourceFormat to $targetFormat at $bitrate?\n\nThe original file will be deleted after conversion.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Convert from $sourceFormat to $targetFormat? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Lossless conversion — no quality loss';
+
   @override
   String get trackConvertConverting => 'Converting audio...';
 
@@ -2452,6 +2465,17 @@ class AppLocalizationsPt extends AppLocalizations {
     return 'Convert $count $_temp0 to $format at $bitrate?\n\nOriginal files will be deleted after conversion.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Converting $current of $total...';

lib/l10n/app_localizations_ru.dart

@@ -2252,6 +2252,18 @@ class AppLocalizationsRu extends AppLocalizations {
     return 'Конвертировать из $sourceFormat в $targetFormat $bitrate?\n\nОригинальный файл будет удален после конвертации.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Convert from $sourceFormat to $targetFormat? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Lossless conversion — no quality loss';
+
   @override
   String get trackConvertConverting => 'Конвертация аудио...';
 
@@ -2511,6 +2523,17 @@ class AppLocalizationsRu extends AppLocalizations {
     return 'Convert $count $_temp0 to $format at $bitrate?\n\nOriginal files will be deleted after conversion.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Конвертация $current из $total...';

lib/l10n/app_localizations_tr.dart

@@ -2211,6 +2211,18 @@ class AppLocalizationsTr extends AppLocalizations {
     return 'Convert from $sourceFormat to $targetFormat at $bitrate?\n\nThe original file will be deleted after conversion.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Convert from $sourceFormat to $targetFormat? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Lossless conversion — no quality loss';
+
   @override
   String get trackConvertConverting => 'Converting audio...';
 
@@ -2464,6 +2476,17 @@ class AppLocalizationsTr extends AppLocalizations {
     return 'Convert $count $_temp0 to $format at $bitrate?\n\nOriginal files will be deleted after conversion.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Converting $current of $total...';

lib/l10n/app_localizations_zh.dart

@@ -2176,7 +2176,8 @@ class AppLocalizationsZh extends AppLocalizations {
   String get trackConvertFormat => 'Convert Format';
 
   @override
-  String get trackConvertFormatSubtitle => 'Convert to MP3 or Opus';
+  String get trackConvertFormatSubtitle =>
+      'Convert to MP3, Opus, ALAC, or FLAC';
 
   @override
   String get trackConvertTitle => 'Convert Audio';
@@ -2199,6 +2200,18 @@ class AppLocalizationsZh extends AppLocalizations {
     return 'Convert from $sourceFormat to $targetFormat at $bitrate?\n\nThe original file will be deleted after conversion.';
   }
 
+  @override
+  String trackConvertConfirmMessageLossless(
+    String sourceFormat,
+    String targetFormat,
+  ) {
+    return 'Convert from $sourceFormat to $targetFormat? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.';
+  }
+
+  @override
+  String get trackConvertLosslessHint =>
+      'Lossless conversion — no quality loss';
+
   @override
   String get trackConvertConverting => 'Converting audio...';
 
@@ -2452,6 +2465,17 @@ class AppLocalizationsZh extends AppLocalizations {
     return 'Convert $count $_temp0 to $format at $bitrate?\n\nOriginal files will be deleted after conversion.';
   }
 
+  @override
+  String selectionBatchConvertConfirmMessageLossless(int count, String format) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'tracks',
+      one: 'track',
+    );
+    return 'Convert $count $_temp0 to $format? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.';
+  }
+
   @override
   String selectionBatchConvertProgress(int current, int total) {
     return 'Converting $current of $total...';

lib/l10n/arb/app_en.arb

@@ -2873,7 +2873,7 @@
   "@trackConvertFormat": {
     "description": "Menu item - convert audio format"
   },
-  "trackConvertFormatSubtitle": "Convert to MP3 or Opus",
+  "trackConvertFormatSubtitle": "Convert to MP3, Opus, ALAC, or FLAC",
   "@trackConvertFormatSubtitle": {
     "description": "Subtitle for convert format menu item"
   },
@@ -2908,6 +2908,22 @@
       }
     }
   },
+  "trackConvertConfirmMessageLossless": "Convert from {sourceFormat} to {targetFormat}? (Lossless — no quality loss)\n\nThe original file will be deleted after conversion.",
+  "@trackConvertConfirmMessageLossless": {
+    "description": "Confirmation dialog message for lossless-to-lossless conversion",
+    "placeholders": {
+      "sourceFormat": {
+        "type": "String"
+      },
+      "targetFormat": {
+        "type": "String"
+      }
+    }
+  },
+  "trackConvertLosslessHint": "Lossless conversion — no quality loss",
+  "@trackConvertLosslessHint": {
+    "description": "Hint shown when converting between lossless formats"
+  },
   "trackConvertConverting": "Converting audio...",
   "@trackConvertConverting": {
     "description": "Snackbar while converting"
@@ -3259,6 +3275,18 @@
       }
     }
   },
+  "selectionBatchConvertConfirmMessageLossless": "Convert {count} {count, plural, =1{track} other{tracks}} to {format}? (Lossless — no quality loss)\n\nOriginal files will be deleted after conversion.",
+  "@selectionBatchConvertConfirmMessageLossless": {
+    "description": "Confirmation dialog message for lossless batch conversion",
+    "placeholders": {
+      "count": {
+        "type": "int"
+      },
+      "format": {
+        "type": "String"
+      }
+    }
+  },
   "selectionBatchConvertProgress": "Converting {current} of {total}...",
   "@selectionBatchConvertProgress": {
     "description": "Snackbar during batch conversion progress",

lib/l10n/arb/app_id.arb

@@ -2809,7 +2809,7 @@
   "@trackConvertFormat": {
     "description": "Menu item - convert audio format"
   },
-  "trackConvertFormatSubtitle": "Convert to MP3 or Opus",
+  "trackConvertFormatSubtitle": "Konversi ke MP3, Opus, ALAC, atau FLAC",
   "@trackConvertFormatSubtitle": {
     "description": "Subtitle for convert format menu item"
   },
@@ -2844,6 +2844,22 @@
       }
     }
   },
+  "trackConvertConfirmMessageLossless": "Konversi dari {sourceFormat} ke {targetFormat}? (Lossless — tanpa kehilangan kualitas)\n\nFile asli akan dihapus setelah konversi.",
+  "@trackConvertConfirmMessageLossless": {
+    "description": "Confirmation dialog message for lossless-to-lossless conversion",
+    "placeholders": {
+      "sourceFormat": {
+        "type": "String"
+      },
+      "targetFormat": {
+        "type": "String"
+      }
+    }
+  },
+  "trackConvertLosslessHint": "Konversi lossless — tanpa kehilangan kualitas",
+  "@trackConvertLosslessHint": {
+    "description": "Hint shown when converting between lossless formats"
+  },
   "trackConvertConverting": "Converting audio...",
   "@trackConvertConverting": {
     "description": "Snackbar while converting"

lib/screens/downloaded_album_screen.dart

@@ -912,6 +912,7 @@ class _DownloadedAlbumScreenState extends ConsumerState<DownloadedAlbumScreen> {
   ) {
     String selectedFormat = 'MP3';
     String selectedBitrate = '320k';
+    bool isLosslessTarget = false;
 
     showModalBottomSheet(
       context: context,
@@ -923,7 +924,7 @@ class _DownloadedAlbumScreenState extends ConsumerState<DownloadedAlbumScreen> {
         return StatefulBuilder(
           builder: (context, setSheetState) {
             final colorScheme = Theme.of(context).colorScheme;
-            final formats = ['MP3', 'Opus'];
+            final formats = ['ALAC', 'FLAC', 'MP3', 'Opus'];
             final bitrates = ['128k', '192k', '256k', '320k'];
 
             return SafeArea(
@@ -960,51 +961,75 @@ class _DownloadedAlbumScreenState extends ConsumerState<DownloadedAlbumScreen> {
                       ),
                     ),
                     const SizedBox(height: 8),
-                    Row(
-                      children: formats.map((format) {
-                        final isSelected = format == selectedFormat;
-                        return Padding(
-                          padding: const EdgeInsets.only(right: 8),
-                          child: ChoiceChip(
-                            label: Text(format),
-                            selected: isSelected,
-                            onSelected: (selected) {
-                              if (selected) {
-                                setSheetState(() {
-                                  selectedFormat = format;
-                                  selectedBitrate = format == 'Opus'
-                                      ? '128k'
-                                      : '320k';
-                                });
-                              }
-                            },
-                          ),
-                        );
-                      }).toList(),
-                    ),
-                    const SizedBox(height: 16),
-                    Text(
-                      context.l10n.trackConvertBitrate,
-                      style: Theme.of(context).textTheme.titleSmall?.copyWith(
-                        color: colorScheme.onSurfaceVariant,
-                      ),
-                    ),
-                    const SizedBox(height: 8),
                     Wrap(
                       spacing: 8,
-                      children: bitrates.map((br) {
-                        final isSelected = br == selectedBitrate;
+                      children: formats.map((format) {
+                        final isSelected = format == selectedFormat;
                         return ChoiceChip(
-                          label: Text(br),
+                          label: Text(format),
                           selected: isSelected,
                           onSelected: (selected) {
                             if (selected) {
-                              setSheetState(() => selectedBitrate = br);
+                              setSheetState(() {
+                                selectedFormat = format;
+                                isLosslessTarget =
+                                    format == 'ALAC' || format == 'FLAC';
+                                if (!isLosslessTarget) {
+                                  selectedBitrate =
+                                      format == 'Opus' ? '128k' : '320k';
+                                }
+                              });
                             }
                           },
                         );
                       }).toList(),
                     ),
+                    if (!isLosslessTarget) ...[
+                      const SizedBox(height: 16),
+                      Text(
+                        context.l10n.trackConvertBitrate,
+                        style: Theme.of(context).textTheme.titleSmall?.copyWith(
+                          color: colorScheme.onSurfaceVariant,
+                        ),
+                      ),
+                      const SizedBox(height: 8),
+                      Wrap(
+                        spacing: 8,
+                        children: bitrates.map((br) {
+                          final isSelected = br == selectedBitrate;
+                          return ChoiceChip(
+                            label: Text(br),
+                            selected: isSelected,
+                            onSelected: (selected) {
+                              if (selected) {
+                                setSheetState(() => selectedBitrate = br);
+                              }
+                            },
+                          );
+                        }).toList(),
+                      ),
+                    ],
+                    if (isLosslessTarget) ...[
+                      const SizedBox(height: 16),
+                      Row(
+                        children: [
+                          Icon(
+                            Icons.verified,
+                            size: 16,
+                            color: colorScheme.primary,
+                          ),
+                          const SizedBox(width: 6),
+                          Text(
+                            context.l10n.trackConvertLosslessHint,
+                            style: Theme.of(
+                              context,
+                            ).textTheme.bodySmall?.copyWith(
+                              color: colorScheme.primary,
+                            ),
+                          ),
+                        ],
+                      ),
+                    ],
                     const SizedBox(height: 24),
                     SizedBox(
                       width: double.infinity,
@@ -1057,12 +1082,19 @@ class _DownloadedAlbumScreenState extends ConsumerState<DownloadedAlbumScreen> {
           : item.filePath.toLowerCase();
       final ext = nameToCheck.endsWith('.flac')
           ? 'FLAC'
+          : nameToCheck.endsWith('.m4a')
+          ? 'M4A'
           : nameToCheck.endsWith('.mp3')
           ? 'MP3'
           : (nameToCheck.endsWith('.opus') || nameToCheck.endsWith('.ogg'))
           ? 'Opus'
           : null;
-      if (ext != null && ext != targetFormat) selected.add(item);
+      if (ext == null || ext == targetFormat) continue;
+      // Skip lossy sources when target is lossless (pointless re-encoding)
+      final isLosslessTarget = targetFormat == 'ALAC' || targetFormat == 'FLAC';
+      final isLosslessSource = ext == 'FLAC' || ext == 'M4A';
+      if (isLosslessTarget && !isLosslessSource) continue;
+      selected.add(item);
     }
 
     if (selected.isEmpty) {
@@ -1074,16 +1106,22 @@ class _DownloadedAlbumScreenState extends ConsumerState<DownloadedAlbumScreen> {
       return;
     }
 
+    final isLossless = targetFormat == 'ALAC' || targetFormat == 'FLAC';
     final confirmed = await showDialog<bool>(
       context: context,
       builder: (ctx) => AlertDialog(
         title: Text(context.l10n.selectionBatchConvertConfirmTitle),
         content: Text(
-          context.l10n.selectionBatchConvertConfirmMessage(
-            selected.length,
-            targetFormat,
-            bitrate,
-          ),
+          isLossless
+              ? context.l10n.selectionBatchConvertConfirmMessageLossless(
+                  selected.length,
+                  targetFormat,
+                )
+              : context.l10n.selectionBatchConvertConfirmMessage(
+                  selected.length,
+                  targetFormat,
+                  bitrate,
+                ),
         ),
         actions: [
           TextButton(
@@ -1103,8 +1141,10 @@ class _DownloadedAlbumScreenState extends ConsumerState<DownloadedAlbumScreen> {
     int successCount = 0;
     final total = selected.length;
     final historyDb = HistoryDatabase.instance;
-    final newQuality =
-        '${targetFormat.toUpperCase()} ${bitrate.trim().toLowerCase()}';
+    final newQuality = (targetFormat.toUpperCase() == 'ALAC' ||
+            targetFormat.toUpperCase() == 'FLAC')
+        ? '${targetFormat.toUpperCase()} Lossless'
+        : '${targetFormat.toUpperCase()} ${bitrate.trim().toLowerCase()}';
     final settings = ref.read(settingsProvider);
     final shouldEmbedLyrics =
         settings.embedLyrics && settings.lyricsMode != 'external';
@@ -1207,13 +1247,27 @@ class _DownloadedAlbumScreenState extends ConsumerState<DownloadedAlbumScreen> {
             final baseName = dotIdx > 0
                 ? oldFileName.substring(0, dotIdx)
                 : oldFileName;
-            final newExt = targetFormat.toLowerCase() == 'opus'
-                ? '.opus'
-                : '.mp3';
+            String newExt;
+            String mimeType;
+            switch (targetFormat.toLowerCase()) {
+              case 'opus':
+                newExt = '.opus';
+                mimeType = 'audio/opus';
+                break;
+              case 'alac':
+                newExt = '.m4a';
+                mimeType = 'audio/mp4';
+                break;
+              case 'flac':
+                newExt = '.flac';
+                mimeType = 'audio/flac';
+                break;
+              default:
+                newExt = '.mp3';
+                mimeType = 'audio/mpeg';
+                break;
+            }
             final newFileName = '$baseName$newExt';
-            final mimeType = targetFormat.toLowerCase() == 'opus'
-                ? 'audio/opus'
-                : 'audio/mpeg';
 
             final safUri = await PlatformBridge.createSafFileFromPath(
               treeUri: treeUri,

lib/screens/local_album_screen.dart

@@ -1131,6 +1131,7 @@ class _LocalAlbumScreenState extends ConsumerState<LocalAlbumScreen> {
   ) {
     String selectedFormat = 'MP3';
     String selectedBitrate = '320k';
+    bool isLosslessTarget = false;
 
     showModalBottomSheet(
       context: context,
@@ -1142,7 +1143,7 @@ class _LocalAlbumScreenState extends ConsumerState<LocalAlbumScreen> {
         return StatefulBuilder(
           builder: (context, setSheetState) {
             final colorScheme = Theme.of(context).colorScheme;
-            final formats = ['MP3', 'Opus'];
+            final formats = ['ALAC', 'FLAC', 'MP3', 'Opus'];
             final bitrates = ['128k', '192k', '256k', '320k'];
 
             return SafeArea(
@@ -1179,51 +1180,75 @@ class _LocalAlbumScreenState extends ConsumerState<LocalAlbumScreen> {
                       ),
                     ),
                     const SizedBox(height: 8),
-                    Row(
-                      children: formats.map((format) {
-                        final isSelected = format == selectedFormat;
-                        return Padding(
-                          padding: const EdgeInsets.only(right: 8),
-                          child: ChoiceChip(
-                            label: Text(format),
-                            selected: isSelected,
-                            onSelected: (selected) {
-                              if (selected) {
-                                setSheetState(() {
-                                  selectedFormat = format;
-                                  selectedBitrate = format == 'Opus'
-                                      ? '128k'
-                                      : '320k';
-                                });
-                              }
-                            },
-                          ),
-                        );
-                      }).toList(),
-                    ),
-                    const SizedBox(height: 16),
-                    Text(
-                      context.l10n.trackConvertBitrate,
-                      style: Theme.of(context).textTheme.titleSmall?.copyWith(
-                        color: colorScheme.onSurfaceVariant,
-                      ),
-                    ),
-                    const SizedBox(height: 8),
                     Wrap(
                       spacing: 8,
-                      children: bitrates.map((br) {
-                        final isSelected = br == selectedBitrate;
+                      children: formats.map((format) {
+                        final isSelected = format == selectedFormat;
                         return ChoiceChip(
-                          label: Text(br),
+                          label: Text(format),
                           selected: isSelected,
                           onSelected: (selected) {
                             if (selected) {
-                              setSheetState(() => selectedBitrate = br);
+                              setSheetState(() {
+                                selectedFormat = format;
+                                isLosslessTarget =
+                                    format == 'ALAC' || format == 'FLAC';
+                                if (!isLosslessTarget) {
+                                  selectedBitrate =
+                                      format == 'Opus' ? '128k' : '320k';
+                                }
+                              });
                             }
                           },
                         );
                       }).toList(),
                     ),
+                    if (!isLosslessTarget) ...[
+                      const SizedBox(height: 16),
+                      Text(
+                        context.l10n.trackConvertBitrate,
+                        style: Theme.of(context).textTheme.titleSmall?.copyWith(
+                          color: colorScheme.onSurfaceVariant,
+                        ),
+                      ),
+                      const SizedBox(height: 8),
+                      Wrap(
+                        spacing: 8,
+                        children: bitrates.map((br) {
+                          final isSelected = br == selectedBitrate;
+                          return ChoiceChip(
+                            label: Text(br),
+                            selected: isSelected,
+                            onSelected: (selected) {
+                              if (selected) {
+                                setSheetState(() => selectedBitrate = br);
+                              }
+                            },
+                          );
+                        }).toList(),
+                      ),
+                    ],
+                    if (isLosslessTarget) ...[
+                      const SizedBox(height: 16),
+                      Row(
+                        children: [
+                          Icon(
+                            Icons.verified,
+                            size: 16,
+                            color: colorScheme.primary,
+                          ),
+                          const SizedBox(width: 6),
+                          Text(
+                            context.l10n.trackConvertLosslessHint,
+                            style: Theme.of(
+                              context,
+                            ).textTheme.bodySmall?.copyWith(
+                              color: colorScheme.primary,
+                            ),
+                          ),
+                        ],
+                      ),
+                    ],
                     const SizedBox(height: 24),
                     SizedBox(
                       width: double.infinity,
@@ -1276,6 +1301,8 @@ class _LocalAlbumScreenState extends ConsumerState<LocalAlbumScreen> {
         final fmt = item.format!.toLowerCase();
         if (fmt == 'flac') {
           currentFormat = 'FLAC';
+        } else if (fmt == 'm4a') {
+          currentFormat = 'M4A';
         } else if (fmt == 'mp3') {
           currentFormat = 'MP3';
         } else if (fmt == 'opus' || fmt == 'ogg') {
@@ -1287,15 +1314,20 @@ class _LocalAlbumScreenState extends ConsumerState<LocalAlbumScreen> {
         final lower = item.filePath.toLowerCase();
         if (lower.endsWith('.flac')) {
           currentFormat = 'FLAC';
+        } else if (lower.endsWith('.m4a')) {
+          currentFormat = 'M4A';
         } else if (lower.endsWith('.mp3')) {
           currentFormat = 'MP3';
         } else if (lower.endsWith('.opus') || lower.endsWith('.ogg')) {
           currentFormat = 'Opus';
         }
       }
-      if (currentFormat != null && currentFormat != targetFormat) {
-        selected.add(item);
-      }
+      if (currentFormat == null || currentFormat == targetFormat) continue;
+      // Skip lossy sources when target is lossless (pointless re-encoding)
+      final isLosslessTarget = targetFormat == 'ALAC' || targetFormat == 'FLAC';
+      final isLosslessSource = currentFormat == 'FLAC' || currentFormat == 'M4A';
+      if (isLosslessTarget && !isLosslessSource) continue;
+      selected.add(item);
     }
 
     if (selected.isEmpty) {
@@ -1307,16 +1339,22 @@ class _LocalAlbumScreenState extends ConsumerState<LocalAlbumScreen> {
       return;
     }
 
+    final isLossless = targetFormat == 'ALAC' || targetFormat == 'FLAC';
     final confirmed = await showDialog<bool>(
       context: context,
       builder: (ctx) => AlertDialog(
         title: Text(context.l10n.selectionBatchConvertConfirmTitle),
         content: Text(
-          context.l10n.selectionBatchConvertConfirmMessage(
-            selected.length,
-            targetFormat,
-            bitrate,
-          ),
+          isLossless
+              ? context.l10n.selectionBatchConvertConfirmMessageLossless(
+                  selected.length,
+                  targetFormat,
+                )
+              : context.l10n.selectionBatchConvertConfirmMessage(
+                  selected.length,
+                  targetFormat,
+                  bitrate,
+                ),
         ),
         actions: [
           TextButton(
@@ -1481,13 +1519,27 @@ class _LocalAlbumScreenState extends ConsumerState<LocalAlbumScreen> {
             final baseName = dotIdx > 0
                 ? oldFileName.substring(0, dotIdx)
                 : oldFileName;
-            final newExt = targetFormat.toLowerCase() == 'opus'
-                ? '.opus'
-                : '.mp3';
+            String newExt;
+            String mimeType;
+            switch (targetFormat.toLowerCase()) {
+              case 'opus':
+                newExt = '.opus';
+                mimeType = 'audio/opus';
+                break;
+              case 'alac':
+                newExt = '.m4a';
+                mimeType = 'audio/mp4';
+                break;
+              case 'flac':
+                newExt = '.flac';
+                mimeType = 'audio/flac';
+                break;
+              default:
+                newExt = '.mp3';
+                mimeType = 'audio/mpeg';
+                break;
+            }
             final newFileName = '$baseName$newExt';
-            final mimeType = targetFormat.toLowerCase() == 'opus'
-                ? 'audio/opus'
-                : 'audio/mpeg';
 
             final safUri = await PlatformBridge.createSafFileFromPath(
               treeUri: treeUri,

lib/screens/queue_tab.dart

@@ -4757,6 +4757,7 @@ class _QueueTabState extends ConsumerState<QueueTab> {
   ) async {
     String selectedFormat = 'MP3';
     String selectedBitrate = '320k';
+    bool isLosslessTarget = false;
     var didStartConversion = false;
 
     _hideSelectionOverlay();
@@ -4772,7 +4773,7 @@ class _QueueTabState extends ConsumerState<QueueTab> {
         return StatefulBuilder(
           builder: (context, setSheetState) {
             final colorScheme = Theme.of(context).colorScheme;
-            final formats = ['MP3', 'Opus'];
+            final formats = ['ALAC', 'FLAC', 'MP3', 'Opus'];
             final bitrates = ['128k', '192k', '256k', '320k'];
 
             return SafeArea(
@@ -4809,51 +4810,75 @@ class _QueueTabState extends ConsumerState<QueueTab> {
                       ),
                     ),
                     const SizedBox(height: 8),
-                    Row(
-                      children: formats.map((format) {
-                        final isSelected = format == selectedFormat;
-                        return Padding(
-                          padding: const EdgeInsets.only(right: 8),
-                          child: ChoiceChip(
-                            label: Text(format),
-                            selected: isSelected,
-                            onSelected: (selected) {
-                              if (selected) {
-                                setSheetState(() {
-                                  selectedFormat = format;
-                                  selectedBitrate = format == 'Opus'
-                                      ? '128k'
-                                      : '320k';
-                                });
-                              }
-                            },
-                          ),
-                        );
-                      }).toList(),
-                    ),
-                    const SizedBox(height: 16),
-                    Text(
-                      context.l10n.trackConvertBitrate,
-                      style: Theme.of(context).textTheme.titleSmall?.copyWith(
-                        color: colorScheme.onSurfaceVariant,
-                      ),
-                    ),
-                    const SizedBox(height: 8),
                     Wrap(
                       spacing: 8,
-                      children: bitrates.map((br) {
-                        final isSelected = br == selectedBitrate;
+                      children: formats.map((format) {
+                        final isSelected = format == selectedFormat;
                         return ChoiceChip(
-                          label: Text(br),
+                          label: Text(format),
                           selected: isSelected,
                           onSelected: (selected) {
                             if (selected) {
-                              setSheetState(() => selectedBitrate = br);
+                              setSheetState(() {
+                                selectedFormat = format;
+                                isLosslessTarget =
+                                    format == 'ALAC' || format == 'FLAC';
+                                if (!isLosslessTarget) {
+                                  selectedBitrate =
+                                      format == 'Opus' ? '128k' : '320k';
+                                }
+                              });
                             }
                           },
                         );
                       }).toList(),
                     ),
+                    if (!isLosslessTarget) ...[
+                      const SizedBox(height: 16),
+                      Text(
+                        context.l10n.trackConvertBitrate,
+                        style: Theme.of(context).textTheme.titleSmall?.copyWith(
+                          color: colorScheme.onSurfaceVariant,
+                        ),
+                      ),
+                      const SizedBox(height: 8),
+                      Wrap(
+                        spacing: 8,
+                        children: bitrates.map((br) {
+                          final isSelected = br == selectedBitrate;
+                          return ChoiceChip(
+                            label: Text(br),
+                            selected: isSelected,
+                            onSelected: (selected) {
+                              if (selected) {
+                                setSheetState(() => selectedBitrate = br);
+                              }
+                            },
+                          );
+                        }).toList(),
+                      ),
+                    ],
+                    if (isLosslessTarget) ...[
+                      const SizedBox(height: 16),
+                      Row(
+                        children: [
+                          Icon(
+                            Icons.verified,
+                            size: 16,
+                            color: colorScheme.primary,
+                          ),
+                          const SizedBox(width: 6),
+                          Text(
+                            context.l10n.trackConvertLosslessHint,
+                            style: Theme.of(
+                              context,
+                            ).textTheme.bodySmall?.copyWith(
+                              color: colorScheme.primary,
+                            ),
+                          ),
+                        ],
+                      ),
+                    ],
                     const SizedBox(height: 24),
                     SizedBox(
                       width: double.infinity,
@@ -4929,14 +4954,19 @@ class _QueueTabState extends ConsumerState<QueueTab> {
       }
       final ext = nameToCheck.endsWith('.flac')
           ? 'FLAC'
+          : nameToCheck.endsWith('.m4a')
+          ? 'M4A'
           : nameToCheck.endsWith('.mp3')
           ? 'MP3'
           : (nameToCheck.endsWith('.opus') || nameToCheck.endsWith('.ogg'))
           ? 'Opus'
           : null;
-      if (ext != null && ext != targetFormat) {
-        selectedItems.add(item);
-      }
+      if (ext == null || ext == targetFormat) continue;
+      // Skip lossy sources when target is lossless (pointless re-encoding)
+      final isLosslessTarget = targetFormat == 'ALAC' || targetFormat == 'FLAC';
+      final isLosslessSource = ext == 'FLAC' || ext == 'M4A';
+      if (isLosslessTarget && !isLosslessSource) continue;
+      selectedItems.add(item);
     }
 
     if (selectedItems.isEmpty) {
@@ -4949,16 +4979,22 @@ class _QueueTabState extends ConsumerState<QueueTab> {
     }
 
     // Confirm
+    final isLossless = targetFormat == 'ALAC' || targetFormat == 'FLAC';
     final confirmed = await showDialog<bool>(
       context: context,
       builder: (ctx) => AlertDialog(
         title: Text(context.l10n.selectionBatchConvertConfirmTitle),
         content: Text(
-          context.l10n.selectionBatchConvertConfirmMessage(
-            selectedItems.length,
-            targetFormat,
-            bitrate,
-          ),
+          isLossless
+              ? context.l10n.selectionBatchConvertConfirmMessageLossless(
+                  selectedItems.length,
+                  targetFormat,
+                )
+              : context.l10n.selectionBatchConvertConfirmMessage(
+                  selectedItems.length,
+                  targetFormat,
+                  bitrate,
+                ),
         ),
         actions: [
           TextButton(
@@ -4978,8 +5014,10 @@ class _QueueTabState extends ConsumerState<QueueTab> {
     int successCount = 0;
     final total = selectedItems.length;
     final historyDb = HistoryDatabase.instance;
-    final newQuality =
-        '${targetFormat.toUpperCase()} ${bitrate.trim().toLowerCase()}';
+    final newQuality = (targetFormat.toUpperCase() == 'ALAC' ||
+            targetFormat.toUpperCase() == 'FLAC')
+        ? '${targetFormat.toUpperCase()} Lossless'
+        : '${targetFormat.toUpperCase()} ${bitrate.trim().toLowerCase()}';
     final settings = ref.read(settingsProvider);
     final shouldEmbedLyrics =
         settings.embedLyrics && settings.lyricsMode != 'external';
@@ -5093,13 +5131,27 @@ class _QueueTabState extends ConsumerState<QueueTab> {
             final baseName = dotIdx > 0
                 ? oldFileName.substring(0, dotIdx)
                 : oldFileName;
-            final newExt = targetFormat.toLowerCase() == 'opus'
-                ? '.opus'
-                : '.mp3';
+            String newExt;
+            String mimeType;
+            switch (targetFormat.toLowerCase()) {
+              case 'opus':
+                newExt = '.opus';
+                mimeType = 'audio/opus';
+                break;
+              case 'alac':
+                newExt = '.m4a';
+                mimeType = 'audio/mp4';
+                break;
+              case 'flac':
+                newExt = '.flac';
+                mimeType = 'audio/flac';
+                break;
+              default:
+                newExt = '.mp3';
+                mimeType = 'audio/mpeg';
+                break;
+            }
             final newFileName = '$baseName$newExt';
-            final mimeType = targetFormat.toLowerCase() == 'opus'
-                ? 'audio/opus'
-                : 'audio/mpeg';
 
             final safUri = await PlatformBridge.createSafFileFromPath(
               treeUri: treeUri,

lib/screens/track_metadata_screen.dart

@@ -2662,6 +2662,7 @@ class _TrackMetadataScreenState extends ConsumerState<TrackMetadataScreen> {
   bool get _isConvertibleFormat {
     final lower = cleanFilePath.toLowerCase();
     return lower.endsWith('.flac') ||
+        lower.endsWith('.m4a') ||
         lower.endsWith('.mp3') ||
         lower.endsWith('.opus') ||
         lower.endsWith('.ogg');
@@ -2692,6 +2693,7 @@ class _TrackMetadataScreenState extends ConsumerState<TrackMetadataScreen> {
     }
     final lower = cleanFilePath.toLowerCase();
     if (lower.endsWith('.flac')) return 'FLAC';
+    if (lower.endsWith('.m4a')) return 'M4A';
     if (lower.endsWith('.mp3')) return 'MP3';
     if (lower.endsWith('.opus') || lower.endsWith('.ogg')) return 'Opus';
     if (lower.endsWith('.cue')) return 'CUE';
@@ -2749,8 +2751,12 @@ class _TrackMetadataScreenState extends ConsumerState<TrackMetadataScreen> {
   }
 
   String _buildConvertedQualityLabel(String targetFormat, String bitrate) {
+    final upper = targetFormat.toUpperCase();
+    if (upper == 'ALAC' || upper == 'FLAC') {
+      return '$upper Lossless';
+    }
     final normalizedBitrate = bitrate.trim().toLowerCase();
-    return '${targetFormat.toUpperCase()} $normalizedBitrate';
+    return '$upper $normalizedBitrate';
   }
 
   String? _extractLossyBitrateLabel(String? quality) {
@@ -2790,17 +2796,27 @@ class _TrackMetadataScreenState extends ConsumerState<TrackMetadataScreen> {
 
   void _showConvertSheet(BuildContext context) {
     final currentFormat = _currentFileFormat;
-    // Available target formats (exclude current)
-    final formats = <String>[
-      'MP3',
-      'Opus',
-    ].where((f) => f != currentFormat).toList();
+    final isLosslessSource =
+        currentFormat == 'FLAC' || currentFormat == 'M4A';
+
+    // Build available target formats based on source
+    final formats = <String>[];
     if (currentFormat == 'FLAC') {
-      // FLAC can convert to both
+      formats.addAll(['ALAC', 'MP3', 'Opus']);
+    } else if (currentFormat == 'M4A') {
+      formats.addAll(['FLAC', 'MP3', 'Opus']);
+    } else if (currentFormat == 'MP3') {
+      formats.add('Opus');
+    } else if (currentFormat == 'Opus') {
+      formats.add('MP3');
+    } else {
+      formats.addAll(['MP3', 'Opus']);
     }
 
     String selectedFormat = formats.first;
     String selectedBitrate = selectedFormat == 'Opus' ? '128k' : '320k';
+    bool isLosslessTarget =
+        selectedFormat == 'ALAC' || selectedFormat == 'FLAC';
 
     showModalBottomSheet(
       context: context,
@@ -2849,53 +2865,79 @@ class _TrackMetadataScreenState extends ConsumerState<TrackMetadataScreen> {
                       ),
                     ),
                     const SizedBox(height: 8),
-                    Row(
-                      children: formats.map((format) {
-                        final isSelected = format == selectedFormat;
-                        return Padding(
-                          padding: const EdgeInsets.only(right: 8),
-                          child: ChoiceChip(
-                            label: Text(format),
-                            selected: isSelected,
-                            onSelected: (selected) {
-                              if (selected) {
-                                setSheetState(() {
-                                  selectedFormat = format;
-                                  // Reset bitrate to default for format
-                                  selectedBitrate = format == 'Opus'
-                                      ? '128k'
-                                      : '320k';
-                                });
-                              }
-                            },
-                          ),
-                        );
-                      }).toList(),
-                    ),
-                    const SizedBox(height: 16),
-
-                    Text(
-                      context.l10n.trackConvertBitrate,
-                      style: Theme.of(context).textTheme.titleSmall?.copyWith(
-                        color: colorScheme.onSurfaceVariant,
-                      ),
-                    ),
-                    const SizedBox(height: 8),
                     Wrap(
                       spacing: 8,
-                      children: bitrates.map((br) {
-                        final isSelected = br == selectedBitrate;
+                      children: formats.map((format) {
+                        final isSelected = format == selectedFormat;
                         return ChoiceChip(
-                          label: Text(br),
+                          label: Text(format),
                           selected: isSelected,
                           onSelected: (selected) {
                             if (selected) {
-                              setSheetState(() => selectedBitrate = br);
+                              setSheetState(() {
+                                selectedFormat = format;
+                                isLosslessTarget =
+                                    format == 'ALAC' || format == 'FLAC';
+                                if (!isLosslessTarget) {
+                                  selectedBitrate =
+                                      format == 'Opus' ? '128k' : '320k';
+                                }
+                              });
                             }
                           },
                         );
                       }).toList(),
                     ),
+
+                    // Only show bitrate for lossy targets
+                    if (!isLosslessTarget) ...[
+                      const SizedBox(height: 16),
+                      Text(
+                        context.l10n.trackConvertBitrate,
+                        style: Theme.of(context).textTheme.titleSmall?.copyWith(
+                          color: colorScheme.onSurfaceVariant,
+                        ),
+                      ),
+                      const SizedBox(height: 8),
+                      Wrap(
+                        spacing: 8,
+                        children: bitrates.map((br) {
+                          final isSelected = br == selectedBitrate;
+                          return ChoiceChip(
+                            label: Text(br),
+                            selected: isSelected,
+                            onSelected: (selected) {
+                              if (selected) {
+                                setSheetState(() => selectedBitrate = br);
+                              }
+                            },
+                          );
+                        }).toList(),
+                      ),
+                    ],
+
+                    // Show lossless indicator
+                    if (isLosslessTarget && isLosslessSource) ...[
+                      const SizedBox(height: 16),
+                      Row(
+                        children: [
+                          Icon(
+                            Icons.verified,
+                            size: 16,
+                            color: colorScheme.primary,
+                          ),
+                          const SizedBox(width: 6),
+                          Text(
+                            context.l10n.trackConvertLosslessHint,
+                            style: Theme.of(
+                              context,
+                            ).textTheme.bodySmall?.copyWith(
+                              color: colorScheme.primary,
+                            ),
+                          ),
+                        ],
+                      ),
+                    ],
                     const SizedBox(height: 24),
 
                     SizedBox(
@@ -2917,7 +2959,9 @@ class _TrackMetadataScreenState extends ConsumerState<TrackMetadataScreen> {
                           ),
                         ),
                         child: Text(
-                          '$currentFormat  ->  $selectedFormat @ $selectedBitrate',
+                          isLosslessTarget
+                              ? '$currentFormat  ->  $selectedFormat (Lossless)'
+                              : '$currentFormat  ->  $selectedFormat @ $selectedBitrate',
                         ),
                       ),
                     ),
@@ -3402,17 +3446,25 @@ class _TrackMetadataScreenState extends ConsumerState<TrackMetadataScreen> {
     required String targetFormat,
     required String bitrate,
   }) {
+    final isLossless =
+        targetFormat.toUpperCase() == 'ALAC' ||
+        targetFormat.toUpperCase() == 'FLAC';
     showDialog(
       context: context,
       builder: (dialogContext) {
         return AlertDialog(
           title: Text(dialogContext.l10n.trackConvertConfirmTitle),
           content: Text(
-            dialogContext.l10n.trackConvertConfirmMessage(
-              sourceFormat,
-              targetFormat,
-              bitrate,
-            ),
+            isLossless
+                ? dialogContext.l10n.trackConvertConfirmMessageLossless(
+                    sourceFormat,
+                    targetFormat,
+                  )
+                : dialogContext.l10n.trackConvertConfirmMessage(
+                    sourceFormat,
+                    targetFormat,
+                    bitrate,
+                  ),
           ),
           actions: [
             TextButton(
@@ -3561,11 +3613,27 @@ class _TrackMetadataScreenState extends ConsumerState<TrackMetadataScreen> {
         final baseName = dotIdx > 0
             ? oldFileName.substring(0, dotIdx)
             : oldFileName;
-        final newExt = targetFormat.toLowerCase() == 'opus' ? '.opus' : '.mp3';
+        String newExt;
+        String mimeType;
+        switch (targetFormat.toLowerCase()) {
+          case 'opus':
+            newExt = '.opus';
+            mimeType = 'audio/opus';
+            break;
+          case 'alac':
+            newExt = '.m4a';
+            mimeType = 'audio/mp4';
+            break;
+          case 'flac':
+            newExt = '.flac';
+            mimeType = 'audio/flac';
+            break;
+          default: // mp3
+            newExt = '.mp3';
+            mimeType = 'audio/mpeg';
+            break;
+        }
         final newFileName = '$baseName$newExt';
-        final mimeType = targetFormat.toLowerCase() == 'opus'
-            ? 'audio/opus'
-            : 'audio/mpeg';
 
         final safUri = await PlatformBridge.createSafFileFromPath(
           treeUri: treeUri,

lib/services/ffmpeg_service.dart

@@ -1209,7 +1209,8 @@ class FFmpegService {
   }
 
   /// Unified audio format conversion with full metadata + cover preservation.
-  /// Supports: FLAC/MP3/Opus -> MP3/Opus (any direction except same format).
+  /// Supports: FLAC/M4A/MP3/Opus -> MP3/Opus/ALAC/FLAC.
+  /// ALAC and FLAC targets are lossless (bitrate parameter is ignored).
   /// Returns the new file path on success, null on failure.
   static Future<String?> convertAudioFormat({
     required String inputPath,
@@ -1220,11 +1221,30 @@ class FFmpegService {
     bool deleteOriginal = true,
   }) async {
     final format = targetFormat.toLowerCase();
-    if (format != 'mp3' && format != 'opus') {
+    if (!const {'mp3', 'opus', 'alac', 'flac'}.contains(format)) {
       _log.e('Unsupported target format: $targetFormat');
       return null;
     }
 
+    // Lossless targets: dedicated single-pass methods
+    if (format == 'alac') {
+      return _convertToAlac(
+        inputPath: inputPath,
+        metadata: metadata,
+        coverPath: coverPath,
+        deleteOriginal: deleteOriginal,
+      );
+    }
+    if (format == 'flac') {
+      return _convertToFlac(
+        inputPath: inputPath,
+        metadata: metadata,
+        coverPath: coverPath,
+        deleteOriginal: deleteOriginal,
+      );
+    }
+
+    // Lossy targets: MP3 / Opus
     final extension = format == 'opus' ? '.opus' : '.mp3';
     final outputPath = _buildOutputPath(inputPath, extension);
 
@@ -1296,6 +1316,197 @@ class FFmpegService {
     return outputPath;
   }
 
+  /// Convert any audio format to ALAC (Apple Lossless) in an M4A container.
+  /// Metadata and cover art are embedded in a single FFmpeg pass.
+  static Future<String?> _convertToAlac({
+    required String inputPath,
+    required Map<String, String> metadata,
+    String? coverPath,
+    bool deleteOriginal = true,
+  }) async {
+    final outputPath = _buildOutputPath(inputPath, '.m4a');
+
+    final cmdBuffer = StringBuffer();
+    cmdBuffer.write('-i "$inputPath" ');
+
+    // Cover art as second input for M4A attached picture
+    final hasCover = coverPath != null &&
+        coverPath.trim().isNotEmpty &&
+        await File(coverPath).exists();
+    if (hasCover) {
+      cmdBuffer.write('-i "$coverPath" ');
+    }
+
+    cmdBuffer.write('-map 0:a ');
+    if (hasCover) {
+      cmdBuffer.write('-map 1:v -c:v copy -disposition:v:0 attached_pic ');
+    }
+    cmdBuffer.write('-c:a alac ');
+    cmdBuffer.write('-map_metadata -1 ');
+
+    // Embed M4A metadata tags
+    final m4aTags = _convertToM4aTags(metadata);
+    for (final entry in m4aTags.entries) {
+      final sanitized = entry.value.replaceAll('"', '\\"');
+      cmdBuffer.write('-metadata ${entry.key}="$sanitized" ');
+    }
+
+    cmdBuffer.write('"$outputPath" -y');
+
+    _log.i(
+      'Converting ${inputPath.split(Platform.pathSeparator).last} to ALAC',
+    );
+    final result = await _execute(cmdBuffer.toString());
+
+    if (!result.success) {
+      _log.e('ALAC conversion failed: ${result.output}');
+      return null;
+    }
+
+    if (deleteOriginal) {
+      try {
+        await File(inputPath).delete();
+        _log.i(
+          'Deleted original: ${inputPath.split(Platform.pathSeparator).last}',
+        );
+      } catch (e) {
+        _log.w('Failed to delete original: $e');
+      }
+    }
+
+    return outputPath;
+  }
+
+  /// Convert any audio format to FLAC.
+  /// Metadata (Vorbis comments) and cover art (METADATA_BLOCK_PICTURE) are
+  /// embedded in a single FFmpeg pass.
+  static Future<String?> _convertToFlac({
+    required String inputPath,
+    required Map<String, String> metadata,
+    String? coverPath,
+    bool deleteOriginal = true,
+  }) async {
+    final outputPath = _buildOutputPath(inputPath, '.flac');
+
+    final cmdBuffer = StringBuffer();
+    cmdBuffer.write('-i "$inputPath" ');
+    cmdBuffer.write('-map 0:a ');
+    cmdBuffer.write('-c:a flac -compression_level 8 ');
+    cmdBuffer.write('-map_metadata -1 ');
+
+    // Embed Vorbis comments
+    for (final entry in metadata.entries) {
+      if (entry.value.trim().isEmpty) continue;
+      final sanitized = entry.value.replaceAll('"', '\\"');
+      cmdBuffer.write('-metadata ${entry.key}="$sanitized" ');
+    }
+
+    // Embed cover art via METADATA_BLOCK_PICTURE (same approach as Opus)
+    if (coverPath != null && coverPath.trim().isNotEmpty) {
+      try {
+        if (await File(coverPath).exists()) {
+          final pictureBlock = await _createMetadataBlockPicture(coverPath);
+          if (pictureBlock != null) {
+            final escapedBlock = pictureBlock.replaceAll('"', '\\"');
+            cmdBuffer.write(
+              '-metadata METADATA_BLOCK_PICTURE="$escapedBlock" ',
+            );
+            _log.d(
+              'Created METADATA_BLOCK_PICTURE for FLAC (${pictureBlock.length} chars)',
+            );
+          }
+        }
+      } catch (e) {
+        _log.e('Error creating METADATA_BLOCK_PICTURE for FLAC: $e');
+      }
+    }
+
+    cmdBuffer.write('"$outputPath" -y');
+
+    _log.i(
+      'Converting ${inputPath.split(Platform.pathSeparator).last} to FLAC',
+    );
+    final result = await _execute(cmdBuffer.toString());
+
+    if (!result.success) {
+      _log.e('FLAC conversion failed: ${result.output}');
+      return null;
+    }
+
+    if (deleteOriginal) {
+      try {
+        await File(inputPath).delete();
+        _log.i(
+          'Deleted original: ${inputPath.split(Platform.pathSeparator).last}',
+        );
+      } catch (e) {
+        _log.w('Failed to delete original: $e');
+      }
+    }
+
+    return outputPath;
+  }
+
+  /// Map Vorbis comment keys to M4A/MP4 metadata tag names for FFmpeg.
+  static Map<String, String> _convertToM4aTags(
+    Map<String, String> metadata,
+  ) {
+    final m4aMap = <String, String>{};
+
+    for (final entry in metadata.entries) {
+      final key = entry.key.toUpperCase().replaceAll(RegExp(r'[^A-Z0-9]'), '');
+      final value = entry.value;
+      if (value.trim().isEmpty) continue;
+
+      switch (key) {
+        case 'TITLE':
+          m4aMap['title'] = value;
+          break;
+        case 'ARTIST':
+          m4aMap['artist'] = value;
+          break;
+        case 'ALBUM':
+          m4aMap['album'] = value;
+          break;
+        case 'ALBUMARTIST':
+          m4aMap['album_artist'] = value;
+          break;
+        case 'TRACKNUMBER':
+        case 'TRACK':
+        case 'TRCK':
+          m4aMap['track'] = value;
+          break;
+        case 'DISCNUMBER':
+        case 'DISC':
+        case 'TPOS':
+          m4aMap['disc'] = value;
+          break;
+        case 'DATE':
+        case 'YEAR':
+          m4aMap['date'] = value;
+          break;
+        case 'GENRE':
+          m4aMap['genre'] = value;
+          break;
+        case 'COMPOSER':
+          m4aMap['composer'] = value;
+          break;
+        case 'COMMENT':
+          m4aMap['comment'] = value;
+          break;
+        case 'COPYRIGHT':
+          m4aMap['copyright'] = value;
+          break;
+        case 'LYRICS':
+        case 'UNSYNCEDLYRICS':
+          m4aMap['lyrics'] = value;
+          break;
+      }
+    }
+
+    return m4aMap;
+  }
+
   static Map<String, String> _convertToId3Tags(
     Map<String, String> vorbisMetadata,
   ) {