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fix: preserve metadata and cover art in ALAC/M4A to FLAC conversion

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- Use -map_metadata 0 instead of -map_metadata -1 so FFmpeg copies and
  auto-remaps source tags (M4A/ID3 → Vorbis comments) as a base
- Add _normalizeToVorbisComments() to filter technical fields (BIT_DEPTH,
  SAMPLE_RATE, DURATION) and normalize key variations to standard Vorbis
  comment names before applying overrides
- Switch cover art embedding from METADATA_BLOCK_PICTURE base64 (unreliable
  on Android due to command-line length limits) to -i cover -map 1:v
  -disposition attached_pic (same proven approach as embedMetadata and
  _convertToAlac)
- Drop zero-value track/disc numbers from override map to prevent
  clobbering source metadata with '0' from Go readFileMetadata
This commit is contained in:
zarzet
2026-03-16 02:26:53 +07:00
parent b8af75bf6e
commit 554fe08fcd
1 changed files with 101 additions and 28 deletions
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lib/services/ffmpeg_service.dart
+101 -28
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@@ -1378,8 +1378,11 @@ class FFmpegService {
}
/// Convert any audio format to FLAC.
/// Metadata (Vorbis comments) and cover art (METADATA_BLOCK_PICTURE) are
/// embedded in a single FFmpeg pass.
/// Source metadata is preserved via -map_metadata 0 (FFmpeg auto-remaps
/// tag names between container formats), then explicit Vorbis comment
/// overrides are applied from the [metadata] map.
/// Cover art is embedded via a second input stream (same approach as
/// [embedMetadata] and [_convertToAlac]).
static Future<String?> _convertToFlac({
required String inputPath,
required Map<String, String> metadata,
@@ -1390,35 +1393,32 @@ class FFmpegService {
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" ');
// Cover art as second input for attached picture
final hasCover = coverPath != null &&
coverPath.trim().isNotEmpty &&
await File(coverPath).exists();
if (hasCover) {
cmdBuffer.write('-i "$coverPath" ');
}
// Embed cover art via METADATA_BLOCK_PICTURE (same approach as Opus)
if (coverPath != null && coverPath.trim().isNotEmpty) {
try {
if (await File(coverPath).exists()) {
final pictureBlock = await _createMetadataBlockPicture(coverPath);
if (pictureBlock != null) {
final escapedBlock = pictureBlock.replaceAll('"', '\\"');
cmdBuffer.write(
'-metadata METADATA_BLOCK_PICTURE="$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('-map 0:a ');
if (hasCover) {
cmdBuffer.write('-map 1:v -c:v copy -disposition:v:0 attached_pic ');
cmdBuffer.write('-metadata:s:v title="Album cover" ');
cmdBuffer.write('-metadata:s:v comment="Cover (front)" ');
}
cmdBuffer.write('-c:a flac -compression_level 8 ');
// Copy source metadata as base (FFmpeg auto-remaps M4A/ID3 tags to
// Vorbis comment names), then override with our explicit values.
cmdBuffer.write('-map_metadata 0 ');
// Apply normalized Vorbis comment overrides
final vorbisComments = _normalizeToVorbisComments(metadata);
for (final entry in vorbisComments.entries) {
final sanitized = entry.value.replaceAll('"', '\\"');
cmdBuffer.write('-metadata ${entry.key}="$sanitized" ');
}
cmdBuffer.write('"$outputPath" -y');
@@ -1447,6 +1447,79 @@ class FFmpegService {
return outputPath;
}
/// Normalize metadata keys to standard Vorbis comment names and filter out
/// technical/non-tag fields (bit_depth, sample_rate, duration, etc.).
static Map<String, String> _normalizeToVorbisComments(
Map<String, String> metadata,
) {
final vorbis = <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':
vorbis['TITLE'] = value;
break;
case 'ARTIST':
vorbis['ARTIST'] = value;
break;
case 'ALBUM':
vorbis['ALBUM'] = value;
break;
case 'ALBUMARTIST':
vorbis['ALBUMARTIST'] = value;
break;
case 'TRACKNUMBER':
case 'TRACKNBR':
case 'TRACK':
case 'TRCK':
if (value != '0') vorbis['TRACKNUMBER'] = value;
break;
case 'DISCNUMBER':
case 'DISC':
case 'TPOS':
if (value != '0') vorbis['DISCNUMBER'] = value;
break;
case 'DATE':
case 'YEAR':
vorbis['DATE'] = value;
break;
case 'GENRE':
vorbis['GENRE'] = value;
break;
case 'ISRC':
vorbis['ISRC'] = value;
break;
case 'LABEL':
case 'ORGANIZATION':
vorbis['ORGANIZATION'] = value;
break;
case 'COPYRIGHT':
vorbis['COPYRIGHT'] = value;
break;
case 'COMPOSER':
vorbis['COMPOSER'] = value;
break;
case 'COMMENT':
vorbis['COMMENT'] = value;
break;
case 'LYRICS':
case 'UNSYNCEDLYRICS':
// Write both keys for compatibility with different FLAC readers
vorbis['LYRICS'] = value;
vorbis['UNSYNCEDLYRICS'] = value;
break;
// Technical fields (BIT_DEPTH, SAMPLE_RATE, DURATION, etc.) are
// intentionally dropped — they are not Vorbis comment tags.
}
}
return vorbis;
}
/// Map Vorbis comment keys to M4A/MP4 metadata tag names for FFmpeg.
static Map<String, String> _convertToM4aTags(
Map<String, String> metadata,