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Skip leading ID3v2 data in MP3 files to allow processing #314

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Merged
merged 2 commits into from
Jan 30, 2022
Merged

Skip leading ID3v2 data in MP3 files to allow processing #314

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ad0cc80
Skip ID3v2 in MP3 files
Jan 9, 2022
be52551
Comment unused code
drewnoakes Jan 30, 2022
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17 changes: 13 additions & 4 deletions MetadataExtractor/Formats/Mpeg/Mp3Reader.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,13 +8,24 @@ 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();

// If the file starts with ID3v2 data, try to skip over it for now.
// Eventually we should extract this data properly.
if ((header & 0xFFFFFF00) == 0x49443300) // "ID3"
{
// Adjust start to end of header
var id3Bytes = reader.GetBytes(6);
reader.Skip(id3Bytes[2] * 0x200000 + id3Bytes[3] * 0x4000 + id3Bytes[4] * 0x80 + id3Bytes[5]);
header = reader.GetInt32();
}

// ID: MPEG-2.5, MPEG-2, or MPEG-1
int id = 0;
switch ((header & 0x000180000) >> 19)
Expand Down Expand Up @@ -49,8 +60,7 @@ public Directory Extract(SequentialReader reader)
break;
}


int protectionBit = (header & 0x00010000) >> 16;
// int protectionBit = (header & 0x00010000) >> 16;

// Bitrate: depends on ID and Layer
int bitrate = (header & 0x0000F000) >> 12;
Expand All @@ -75,8 +85,7 @@ public Directory Extract(SequentialReader reader)
frequency = frequencyMapping[1, frequency];
}


int paddingBit = (header & 0x00000200) >> 9;
// int paddingBit = (header & 0x00000200) >> 9;

// Encoding type: Stereo, Joint Stereo, Dual Channel, or Mono
int mode = (header & 0x000000C0) >> 6;
Expand Down
8 changes: 8 additions & 0 deletions MetadataExtractor/Formats/Mpeg/MpegAudioTypeChecker.cs
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Expand Up @@ -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;
Comment on lines +36 to +38
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I think other types of file can start with ID3 too, though this is an improvement over what we had before.


// MPEG audio requires the first 11 bits to be set
if (bytes[0] != 0xFF || (bytes[1] & 0xE0) != 0xE0)
return Util.FileType.Unknown;
Expand Down