feat: cap bit depth/sample rate on lossless conversion + WAV/AIFF

- LosslessConversionQuality model with bit depth/sample rate caps, applied only when they reduce source quality - FFmpegService probes sample rate and appends codec-specific args (-ar, -sample_fmt, -bits_per_raw_sample) for FLAC/ALAC/WAV/AIFF - Batch + single-track convert sheets expose quality cap options - Persist real converted bit depth/sample rate to history/library DB - track_metadata: recognize and convert to WAV/AIFF targets - convertedAudioQualityLabel reflects actual output quality
2026-07-02 19:05:57 +02:00 · 2026-06-29 06:46:19 +07:00
parent e9171d6f21
commit b2074dfd02
6 changed files with 606 additions and 51 deletions
@@ -11,6 +11,7 @@ import 'package:ffmpeg_kit_flutter_new_full/session_state.dart';
 import 'package:path_provider/path_provider.dart';
 import 'package:spotiflac_android/services/platform_bridge.dart';
 import 'package:spotiflac_android/utils/artist_utils.dart';
+import 'package:spotiflac_android/utils/audio_conversion_utils.dart';
 import 'package:spotiflac_android/utils/logger.dart';

 final _log = AppLogger('FFmpeg');
@@ -111,6 +112,16 @@ class DownloadDecryptionDescriptor {
  }
 }

+class _ResolvedLosslessConversionQuality {
+  final int? targetBitDepth;
+  final int? targetSampleRate;
+
+  const _ResolvedLosslessConversionQuality({
+    this.targetBitDepth,
+    this.targetSampleRate,
+  });
+}
+
 class FFmpegService {
  static const int _commandLogPreviewLength = 300;
  static const Duration _liveTunnelStartupTimeout = Duration(seconds: 8);
@@ -306,6 +317,24 @@ class FFmpegService {
    return null;
  }

+  static Future<int?> probeSampleRate(String filePath) async {
+    try {
+      final session = await FFprobeKit.getMediaInformation(filePath);
+      final info = session.getMediaInformation();
+      if (info == null) return null;
+      for (final stream in info.getStreams()) {
+        final props = stream.getAllProperties() ?? const <String, dynamic>{};
+        if (props['codec_type']?.toString() != 'audio') continue;
+        final value = int.tryParse(props['sample_rate']?.toString() ?? '');
+        if (value != null && value > 0) return value;
+        return null;
+      }
+    } catch (e) {
+      _log.w('Sample rate probe failed for $filePath: $e');
+    }
+    return null;
+  }
+
  /// Returns `true` when [filePath] starts with the native FLAC magic bytes
  /// (`fLaC`). Useful to distinguish a real FLAC file from a FLAC-in-MP4
  /// container that carries a `.flac` extension or claims codec=flac.
@@ -328,6 +357,80 @@ class FFmpegService {
    }
  }

+  static Future<_ResolvedLosslessConversionQuality> _resolveLosslessQuality({
+    required String inputPath,
+    required LosslessConversionQuality quality,
+    int? sourceBitDepth,
+  }) async {
+    final probedBitDepth =
+        sourceBitDepth ??
+        (quality.maxBitDepth != null ? await probeBitDepth(inputPath) : null);
+    final probedSampleRate = quality.maxSampleRate != null
+        ? await probeSampleRate(inputPath)
+        : null;
+
+    int? targetBitDepth;
+    if (quality.maxBitDepth != null &&
+        (probedBitDepth == null || probedBitDepth > quality.maxBitDepth!)) {
+      targetBitDepth = quality.maxBitDepth;
+    }
+
+    int? targetSampleRate;
+    if (quality.maxSampleRate != null &&
+        (probedSampleRate == null ||
+            probedSampleRate > quality.maxSampleRate!)) {
+      targetSampleRate = quality.maxSampleRate;
+    }
+
+    return _ResolvedLosslessConversionQuality(
+      targetBitDepth: targetBitDepth,
+      targetSampleRate: targetSampleRate,
+    );
+  }
+
+  static void _appendLosslessCodecQualityArguments(
+    List<String> arguments, {
+    required String codec,
+    int? targetBitDepth,
+    int? targetSampleRate,
+  }) {
+    if (targetSampleRate != null && targetSampleRate > 0) {
+      arguments
+        ..add('-ar')
+        ..add(targetSampleRate.toString());
+    }
+    if (targetBitDepth == null || targetBitDepth <= 0) return;
+
+    if (codec == 'flac') {
+      if (targetBitDepth <= 16) {
+        arguments
+          ..add('-sample_fmt')
+          ..add('s16');
+      } else if (targetBitDepth <= 24) {
+        arguments
+          ..add('-sample_fmt')
+          ..add('s32')
+          ..add('-bits_per_raw_sample')
+          ..add('24');
+      }
+      return;
+    }
+
+    if (codec == 'alac') {
+      if (targetBitDepth <= 16) {
+        arguments
+          ..add('-sample_fmt')
+          ..add('s16p');
+      } else if (targetBitDepth <= 24) {
+        arguments
+          ..add('-sample_fmt')
+          ..add('s32p')
+          ..add('-bits_per_raw_sample')
+          ..add('24');
+      }
+    }
+  }
+
  static Future<String?> convertM4aToFlac(String inputPath) async {
    final outputPath = _buildOutputPath(inputPath, '.flac');

@@ -2048,7 +2151,10 @@ class FFmpegService {
      }

      if (metadata != null) {
-        _appendMappedMetadataToArguments(arguments, _convertToM4aTags(metadata));
+        _appendMappedMetadataToArguments(
+          arguments,
+          _convertToM4aTags(metadata),
+        );
      }

      // MOV muxer accepts codecs the MP4 muxer rejects (e.g. AC-4). The default
@@ -2228,8 +2334,10 @@ class FFmpegService {

  /// Unified audio format conversion with full metadata + cover preservation.
  /// Supports: FLAC/M4A/MP3/Opus -> AAC/M4A/MP3/Opus/ALAC/FLAC/WAV/AIFF.
-  /// ALAC, FLAC, WAV and AIFF targets are lossless (bitrate parameter is ignored).
-  /// [sourceBitDepth] (when known) preserves 24-bit resolution for WAV/AIFF.
+  /// ALAC, FLAC, WAV and AIFF targets are lossless codecs (bitrate parameter
+  /// is ignored). [losslessQuality] can cap bit depth/sample rate, and caps are
+  /// only applied when they reduce the source quality.
+  /// [sourceBitDepth] (when known) avoids an extra probe.
  static Future<String?> convertAudioFormat({
    required String inputPath,
    required String targetFormat,
@@ -2239,6 +2347,8 @@ class FFmpegService {
    String artistTagMode = artistTagModeJoined,
    bool deleteOriginal = true,
    int? sourceBitDepth,
+    LosslessConversionQuality losslessQuality =
+        const LosslessConversionQuality(),
  }) async {
    final format = targetFormat.toLowerCase();
    if (!const {
@@ -2255,11 +2365,21 @@ class FFmpegService {
      return null;
    }

+    final resolvedLosslessQuality = isLosslessConversionTarget(format)
+        ? await _resolveLosslessQuality(
+            inputPath: inputPath,
+            quality: losslessQuality,
+            sourceBitDepth: sourceBitDepth,
+          )
+        : const _ResolvedLosslessConversionQuality();
+
    if (format == 'alac') {
      return _convertToAlac(
        inputPath: inputPath,
        metadata: metadata,
        coverPath: coverPath,
+        targetBitDepth: resolvedLosslessQuality.targetBitDepth,
+        targetSampleRate: resolvedLosslessQuality.targetSampleRate,
        deleteOriginal: deleteOriginal,
      );
    }
@@ -2269,6 +2389,8 @@ class FFmpegService {
        metadata: metadata,
        coverPath: coverPath,
        artistTagMode: artistTagMode,
+        targetBitDepth: resolvedLosslessQuality.targetBitDepth,
+        targetSampleRate: resolvedLosslessQuality.targetSampleRate,
        deleteOriginal: deleteOriginal,
      );
    }
@@ -2279,6 +2401,8 @@ class FFmpegService {
        coverPath: coverPath,
        container: format == 'wav' ? 'wav' : 'aiff',
        sourceBitDepth: sourceBitDepth,
+        targetBitDepth: resolvedLosslessQuality.targetBitDepth,
+        targetSampleRate: resolvedLosslessQuality.targetSampleRate,
        deleteOriginal: deleteOriginal,
      );
    }
@@ -2374,6 +2498,8 @@ class FFmpegService {
    required String inputPath,
    required Map<String, String> metadata,
    String? coverPath,
+    int? targetBitDepth,
+    int? targetSampleRate,
    bool deleteOriginal = true,
  }) async {
    final outputPath = _buildOutputPath(inputPath, '.m4a');
@@ -2407,7 +2533,14 @@ class FFmpegService {
    }
    arguments
      ..add('-c:a')
-      ..add('alac')
+      ..add('alac');
+    _appendLosslessCodecQualityArguments(
+      arguments,
+      codec: 'alac',
+      targetBitDepth: targetBitDepth,
+      targetSampleRate: targetSampleRate,
+    );
+    arguments
      ..add('-map_metadata')
      ..add('-1');

@@ -2418,7 +2551,9 @@ class FFmpegService {
      ..add('-y');

    _log.i(
-      'Converting ${inputPath.split(Platform.pathSeparator).last} to ALAC',
+      'Converting ${inputPath.split(Platform.pathSeparator).last} to ALAC'
+      '${targetBitDepth != null ? ' $targetBitDepth-bit' : ''}'
+      '${targetSampleRate != null ? ' @ ${targetSampleRate}Hz' : ''}',
    );
    final result = await _executeWithArguments(arguments);

@@ -2446,6 +2581,8 @@ class FFmpegService {
    required Map<String, String> metadata,
    String? coverPath,
    String artistTagMode = artistTagModeJoined,
+    int? targetBitDepth,
+    int? targetSampleRate,
    bool deleteOriginal = true,
  }) async {
    final outputPath = _buildOutputPath(inputPath, '.flac');
@@ -2481,7 +2618,14 @@ class FFmpegService {
      ..add('-c:a')
      ..add('flac')
      ..add('-compression_level')
-      ..add('8')
+      ..add('8');
+    _appendLosslessCodecQualityArguments(
+      arguments,
+      codec: 'flac',
+      targetBitDepth: targetBitDepth,
+      targetSampleRate: targetSampleRate,
+    );
+    arguments
      ..add('-map_metadata')
      ..add('0');

@@ -2496,7 +2640,9 @@ class FFmpegService {
      ..add('-y');

    _log.i(
-      'Converting ${inputPath.split(Platform.pathSeparator).last} to FLAC',
+      'Converting ${inputPath.split(Platform.pathSeparator).last} to FLAC'
+      '${targetBitDepth != null ? ' $targetBitDepth-bit' : ''}'
+      '${targetSampleRate != null ? ' @ ${targetSampleRate}Hz' : ''}',
    );
    final result = await _executeWithArguments(arguments);

@@ -2528,11 +2674,13 @@ class FFmpegService {
    required String container, // 'wav' or 'aiff'
    String? coverPath,
    int? sourceBitDepth,
+    int? targetBitDepth,
+    int? targetSampleRate,
    bool deleteOriginal = true,
  }) async {
    final isAiff = container == 'aiff';
    final outputPath = _buildOutputPath(inputPath, isAiff ? '.aiff' : '.wav');
-    var depth = sourceBitDepth;
+    var depth = targetBitDepth ?? sourceBitDepth;
    if (depth == null || depth <= 0) {
      depth = await probeBitDepth(inputPath);
    }
@@ -2542,18 +2690,29 @@ class FFmpegService {
        : (use24 ? 'pcm_s24le' : 'pcm_s16le');

    final arguments = <String>[
-      '-v', 'error', '-hide_banner',
-      '-i', inputPath,
-      '-map', '0:a',
-      '-c:a', codec,
-      '-map_metadata', '-1',
+      '-v',
+      'error',
+      '-hide_banner',
+      '-i',
+      inputPath,
+      '-map',
+      '0:a',
+      '-c:a',
+      codec,
+      if (targetSampleRate != null && targetSampleRate > 0) ...[
+        '-ar',
+        targetSampleRate.toString(),
+      ],
+      '-map_metadata',
+      '-1',
      outputPath,
      '-y',
    ];

    _log.i(
      'Converting ${inputPath.split(Platform.pathSeparator).last} to '
-      '${container.toUpperCase()} (${use24 ? 24 : 16}-bit)',
+      '${container.toUpperCase()} (${use24 ? 24 : 16}-bit'
+      '${targetSampleRate != null ? ', ${targetSampleRate}Hz' : ''})',
    );
    final result = await _executeWithArguments(arguments);
    if (!result.success) {
@@ -1735,6 +1735,8 @@ class LibraryDatabase {
    required String newFilePath,
    required String targetFormat,
    required String bitrate,
+    int? bitDepth,
+    int? sampleRate,
  }) async {
    final db = await database;
    final stat = await fileStat(newFilePath);
@@ -1755,6 +1757,10 @@ class LibraryDatabase {
        normalizedFormat == 'opus' ||
        normalizedFormat == 'aac') {
      updated['bitDepth'] = null;
+      updated['sampleRate'] = null;
+    } else {
+      updated['bitDepth'] = bitDepth ?? item.bitDepth;
+      updated['sampleRate'] = sampleRate ?? item.sampleRate;
    }

    await db.transaction((txn) async {