Added support for MP3 with ID3V2 at start of the files

MetadataExtractor.Tests/Formats/Mpeg/Mp3ReaderTest.cs

@@ -0,0 +1,39 @@
+// Copyright (c) Drew Noakes and contributors. All Rights Reserved. Licensed under the Apache License, Version 2.0. See LICENSE in the project root for license information.
+
+using MetadataExtractor.Formats.Mpeg;
+using MetadataExtractor.IO;
+using Xunit;
+
+namespace MetadataExtractor.Tests.Formats.Mpeg
+{
+    /// <summary>Unit tests for <see cref="Mp3Reader"/>.</summary>
+    public sealed class Mp3ReaderTest
+    {
+        private static Directory ProcessBytes(string file)
+        {
+            using var stream = TestDataUtil.OpenRead(file);
+            return new Mp3Reader().Extract(new SequentialStreamReader(stream));
+        }
+
+        [Fact]
+        public void Mp3()
+        {
+            var directory = ProcessBytes("Data/file_example_MP3_5MG_short.mp3");
+
+            Assert.False(directory.HasError);
+
+            Assert.Equal(320, directory.GetInt32(Mp3Directory.TagBitrate));
+        }
+
+        [Fact]
+        public void Mp3_IDV2()
+        {
+            var directory = ProcessBytes("Data/file_example_MP3_5MG.mp3");
+
+            Assert.False(directory.HasError);
+
+            Assert.Equal(320, directory.GetInt32(Mp3Directory.TagBitrate));
+        }
+
+    }
+}

MetadataExtractor/Formats/Mpeg/Mp3Reader.cs

@@ -8,13 +8,23 @@ public sealed class Mp3Reader
     {
         // http://id3.org/mp3Frame
         // https://www.loc.gov/preservation/digital/formats/fdd/fdd000105.shtml
+        // https://id3.org/id3v2.4.0-structure
 
         public Directory Extract(SequentialReader reader)
         {
             var directory = new Mp3Directory();
 
             var header = reader.GetInt32();
 
+            // Support ID3V2 - starts at the beginning of a MP3 file
+            if ((header & 0xFFFFFF00) == 0x49443300)
+            {
+                // Adjust start to end of header
+                var id3Bytes = reader.GetBytes(6);
+                reader.Skip(id3Bytes[2] * 2097152 + id3Bytes[3] * 16384 + id3Bytes[4] * 128 + id3Bytes[5]);
+                header = reader.GetInt32();
+            }
+
             // ID: MPEG-2.5, MPEG-2, or MPEG-1
             int id = 0;
             switch ((header & 0x000180000) >> 19)

MetadataExtractor/Formats/Mpeg/MpegAudioTypeChecker.cs

@@ -23,12 +23,20 @@ 2   Layer description
                 11 - Layer I
 
             Additional bits contain more information, but are not required for file type identification.
+
+            MP3 with ID3V2-Tags https://id3.org/id3v2.4.0-structure
+            MP3-File with ID3V2-Tagging at start
          */
 
         public int ByteCount => 3;
 
         public Util.FileType CheckType(byte[] bytes)
         {
+
+            // MP3-File with "ID3" at start
+            if (bytes[0] == 0x49 && bytes[1] == 0x44 && bytes[2] == 0x33)
+                return Util.FileType.Mp3;
+
             // MPEG audio requires the first 11 bits to be set
             if (bytes[0] != 0xFF || (bytes[1] & 0xE0) != 0xE0)
                 return Util.FileType.Unknown;