Fixes to mp3 parser and writer

lib/src/parser.dart

@@ -25,9 +25,11 @@ AudioMetadata readMetadata(File track, {bool getImage = false}) {
       final a = AudioMetadata(
         file: track,
         album: mp3Metadata.album,
-        artist: mp3Metadata.bandOrOrchestra ??
-            mp3Metadata.leadPerformer ??
-            mp3Metadata.originalArtist,
+        artist: (mp3Metadata.bandOrOrchestra?.isNotEmpty ?? false)
+            ? mp3Metadata.bandOrOrchestra
+            : (mp3Metadata.leadPerformer?.isNotEmpty ?? false)
+                ? mp3Metadata.leadPerformer
+                : mp3Metadata.originalArtist,
         bitrate: mp3Metadata.bitrate,
         duration: mp3Metadata.duration,
         language: mp3Metadata.languages,

lib/src/writers/id3v4_writer.dart

@@ -184,12 +184,13 @@ class Id3v4Writer extends BaseMetadataWriter<Mp3Metadata> {
   void _writeFrame(BytesBuilder builder, String frameId, String data) {
     builder.add(frameId.codeUnits);
 
-    builder.add(_encodeSynchsafeInteger(data.length + 1));
+    final encodedData = utf8.encode(data);
+    builder.add(_encodeSynchsafeInteger(encodedData.length + 1));
     // flags
     builder.add([0, 0]);
 
     builder.addByte(0x03);
-    builder.add(utf8.encode(data));
+    builder.add(encodedData);
   }
 
   void _writeFrameWithBytes(

test/mp3/mp3_parser_test.dart

@@ -69,4 +69,15 @@ void main() {
     expect(result.duration, isNotNull);
     expect(result.duration!.inMilliseconds, closeTo(310, 5));
   });
+
+
+  test("Parse MP3 file with cyrillic symbols", () {
+    final track = File('./test/mp3/cyrillic_symbols.mp3');
+    final result = readMetadata(track, getImage: false);
+
+    expect(result.album, equals("Альбом"));
+    expect(result.artist, equals("Артист"));
+    expect(result.title, equals("Название"));
+    expect(result.lyrics, equals("Текст"));
+  });
 }

test/writers/id3v4_writer_test.dart

@@ -126,6 +126,95 @@ void main() {
           expect(picture.bytes, equals([0, 1, 2, 3]));
         },
       );
+
+      test(
+        "Write metadata with cyrillic symbols",
+        () {
+          final writer = Id3v4Writer();
+
+          final file = createTemporaryFile("test.mp3", mp3FrameHeaderCBR());
+
+          final metadata = Mp3Metadata();
+          metadata.songName = "Какое-то название";
+          metadata.originalArtist = "Новый артист";
+          metadata.album = "Самый лучший альбом";
+          metadata.trackNumber = 6;
+          metadata.trackTotal = 12;
+          metadata.year = 2007;
+
+          writer.write(file, metadata);
+
+          final resultMetadata =
+              ID3v2Parser().parse(file.openSync()) as Mp3Metadata;
+
+          expect(resultMetadata.songName, equals(metadata.songName));
+          expect(
+              resultMetadata.originalArtist, equals(metadata.originalArtist));
+          expect(resultMetadata.album, equals(metadata.album));
+          expect(resultMetadata.trackNumber, equals(6));
+          expect(resultMetadata.trackTotal, equals(12));
+          expect(resultMetadata.year, equals(metadata.year));
+        },
+      );
+
+      test(
+        "Write metadata with arabic symbols",
+            () {
+          final writer = Id3v4Writer();
+
+          final file = createTemporaryFile("test.mp3", mp3FrameHeaderCBR());
+
+          final metadata = Mp3Metadata();
+          metadata.songName = "التيتل المعروف";
+          metadata.originalArtist = "التيتل المعروف";
+          metadata.album = "التيتل المعروف";
+          metadata.trackNumber = 6;
+          metadata.trackTotal = 12;
+          metadata.year = 2007;
+
+          writer.write(file, metadata);
+
+          final resultMetadata =
+          ID3v2Parser().parse(file.openSync()) as Mp3Metadata;
+
+          expect(resultMetadata.songName, equals(metadata.songName));
+          expect(
+              resultMetadata.originalArtist, equals(metadata.originalArtist));
+          expect(resultMetadata.album, equals(metadata.album));
+          expect(resultMetadata.trackNumber, equals(6));
+          expect(resultMetadata.trackTotal, equals(12));
+          expect(resultMetadata.year, equals(metadata.year));
+        },
+      );
+
+      test(
+        "Write metadata with chinese symbols",
+            () {
+          final writer = Id3v4Writer();
+
+          final file = createTemporaryFile("test.mp3", mp3FrameHeaderCBR());
+          final metadata = Mp3Metadata();
+          metadata.songName = "这是一个标题";
+          metadata.originalArtist = "新的艺术家";
+          metadata.album = "这是一个标题";
+          metadata.trackNumber = 6;
+          metadata.trackTotal = 12;
+          metadata.year = 2007;
+
+          writer.write(file, metadata);
+
+          final resultMetadata =
+          ID3v2Parser().parse(file.openSync()) as Mp3Metadata;
+
+          expect(resultMetadata.songName, equals(metadata.songName));
+          expect(
+              resultMetadata.originalArtist, equals(metadata.originalArtist));
+          expect(resultMetadata.album, equals(metadata.album));
+          expect(resultMetadata.trackNumber, equals(6));
+          expect(resultMetadata.trackTotal, equals(12));
+          expect(resultMetadata.year, equals(metadata.year));
+        },
+      );
     },
   );
 }