Examples of org.blinkenlights.jid3.MP3File

org.farng.mp3.MP3File

How is MP3 built?

Most people with a little knowledge in MP3 files know that the sound is divided into smaller parts and compressed with a psycoacoustic model. This smaller pieces of the audio is then put into something called 'frames', which is a little datablock with a header. I'll focus on that header in this text.

The header is 4 bytes, 32 bits, big and begins with something called sync. This sync is, at least according to the MPEG standard, 12 set bits in a row. Some add-on standards made later uses 11 set bits and one cleared bit. The sync is directly followed by a ID bit, indicating if the file is a MPEG-1 och MPEG-2 file. 0=MPEG-2 and 1=MPEG-1

The layer is defined with the two layers bits. They are oddly defined as

0 0	Not defined
0 1	Layer III
1 0	Layer II
1 1	Layer I

With this information and the information in the bitrate field we can determine the bitrate of the audio (in kbit/s) according to this table.

Bitrate value	MPEG-1, layer I	MPEG-1, layer II	MPEG-1, layer III	MPEG-2, layer I	MPEG-2, layer II	MPEG-2, layer III
0 0 0 0
0 0 0 1	32	32	32	32	32	8
0 0 1 0	64	48	40	64	48	16
0 0 1 1	96	56	48	96	56	24
0 1 0 0	128	64	56	128	64	32
0 1 0 1	160	80	64	160	80	64
0 1 1 0	192	96	80	192	96	80
0 1 1 1	224	112	96	224	112	56
1 0 0 0	256	128	112	256	128	64
1 0 0 1	288	160	128	288	160	128
1 0 1 0	320	192	160	320	192	160
1 0 1 1	352	224	192	352	224	112
1 1 0 0	384	256	224	384	256	128
1 1 0 1	416	320	256	416	320	256
1 1 1 0	448	384	320	448	384	320
1 1 1 1

The sample rate is described in the frequency field. These values is dependent of which MPEG standard is used according to the following table.

Frequency value	MPEG-1	MPEG-2
0 0	44100 Hz	22050 Hz
0 1	48000 Hz	24000 Hz
1 0	32000 Hz	16000 Hz
1 1

Three bits is not needed in the decoding process at all. These are the copyright bit, original home bit and the private bit. The copyright has the same meaning as the copyright bit on CDs and DAT tapes, i.e. telling that it is illegal to copy the contents if the bit is set. The original home bit indicates, if set, that the frame is located on its original media. No one seems to know what the privat bit is good for.

If the protection bit is NOT set then the frame header is followed by a 16 bit checksum, inserted before the audio data. If the padding bit is set then the frame is padded with an extra byte. Knowing this the size of the complete frame can be calculated with the following formula

FrameSize = 144 * BitRate / SampleRate
when the padding bit is cleared and

FrameSize = (144 * BitRate / SampleRate) + 1
when the padding bit is set.

The frameSize is of course an integer. If for an example BitRate=128000, SampleRate=44100 and the padding bit is cleared, then the FrameSize = 144 * 128000 / 44100 = 417

The mode field is used to tell which sort of stereo/mono encoding that has been used. The purpose of the mode extension field is different for different layers, but I really don't know exactly what it's for.

Mode value	mode
0 0	Stereo
0 1	Joint stereo
1 0	Dual channel
1 1	Mono

The last field is the emphasis field. It is used to sort of 're-equalize' the sound after a Dolby-like noise supression. This is not very used and will probably never be. The following noise supression model is used

Emphasis value	Emphasis method
0 0	none
0 1	50/15ms
1 0
1 1	CCITT j.17

@author Eric Farng @version $Revision: 1.5 $


    public void write(final RandomAccessFile file) throws IOException {
        final String str;
        final Iterator iterator;
        final byte[] buffer = new byte[6];
        final MP3File mp3 = new MP3File();
        mp3.seekMP3Frame(file);
        final long mp3start = file.getFilePointer();
        file.seek(0);
        ID3v2_3Frame frame;
        str = "ID3";
        for (int i = 0; i < str.length(); i++) {

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    public void write(final RandomAccessFile file) throws IOException {
        final String str;
        ID3v2_2Frame frame;
        final Iterator iterator;
        final byte[] buffer = new byte[6];
        final MP3File mp3 = new MP3File();
        mp3.seekMP3Frame(file);
        final long mp3start = file.getFilePointer();
        file.seek(0);


        // write the first 10 tag bytes
        str = "ID3";

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 *
 */
public class TagTestHelpLibrary {


  public static MP3File createMP3FileMockForID3v1(ID3v1 id3){
    MP3File mp3FileMock = EasyMock.createMock(MP3File.class);
    EasyMock.expect(mp3FileMock.hasID3v2Tag()).andReturn(false);
    EasyMock.expect(mp3FileMock.hasID3v1Tag()).andReturn(true);
    EasyMock.expect(mp3FileMock.getID3v1Tag()).andReturn(id3).times(2);
    return mp3FileMock;
  }

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    EasyMock.expect(mp3FileMock.getID3v1Tag()).andReturn(id3).times(2);
    return mp3FileMock;
  }
  
  public static MP3File createMP3FileMockForID3v2(AbstractID3v2 id3){
    MP3File mp3FileMock = EasyMock.createMock(MP3File.class);
    EasyMock.expect(mp3FileMock.hasID3v2Tag()).andReturn(true);
    EasyMock.expect(mp3FileMock.getID3v2Tag()).andReturn(id3).times(2);
    return mp3FileMock;
  }

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    this.testID3v2Genre("(13)", "Pop");
  }


  private void testID3v1Genre(String input, String expectedOutput) throws ID3TagFileException {
    ID3v1 id3Mock = EasyMock.createMock(ID3v1.class);
    MP3File mp3FileMock = TagTestHelpLibrary.createMP3FileMockForID3v1(id3Mock);


    EasyMock.expect(id3Mock.getSongGenre()).andReturn(input);
    EasyMock.replay(id3Mock, mp3FileMock);


    ID3Tag tag = jidID3TagFactory.getID3Tag(mp3FileMock);

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    EasyMock.verify(id3Mock, mp3FileMock);
  }
  
  private void testID3v2Genre(String input, String expectedOutput) throws ID3TagFileException {
    AbstractID3v2 id3Mock = EasyMock.createMock(AbstractID3v2.class);
    MP3File mp3FileMock = TagTestHelpLibrary.createMP3FileMockForID3v2(id3Mock);


    EasyMock.expect(id3Mock.getSongGenre()).andReturn(input);
    EasyMock.replay(id3Mock, mp3FileMock);


    ID3Tag tag = jidID3TagFactory.getID3Tag(mp3FileMock);

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    jidID3TagFactory.getID3Tag(fileMock);
  }
  
  @Test
  public void ID3v1Test() throws ID3TagFileException{
    MP3File mp3FileMock = TagTestHelpLibrary.createMP3FileMockForID3v1(null);
    EasyMock.replay(mp3FileMock);
    
    ID3Tag id3Tag = jidID3TagFactory.getID3Tag(mp3FileMock);
  
    assertTrue(id3Tag.getClass().equals(ID3v1TagImpl.class));

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    EasyMock.verify(mp3FileMock);
  }
  
  @Test
  public void ID3v2Test() throws ID3TagFileException{
    MP3File mp3FileMock = TagTestHelpLibrary.createMP3FileMockForID3v2(null);
    EasyMock.replay(mp3FileMock);
    
    ID3Tag id3Tag = jidID3TagFactory.getID3Tag(mp3FileMock);
  
    assertTrue(id3Tag.getClass().equals(ID3v2TagImpl.class));

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    if (isM4A(file)) {
      throw new ID3M4AException(file);
    }


    try {
      MP3File mp3File = new MP3File(file, NOT_WRITEABLE);
      return getID3Tag(mp3File);


    } catch (IOException e) {
      throw new ID3TagFileException(e, file);
    } catch (TagException e) {

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   *       </ul>
   */
  public static String[] getIDTags(String file) {
    String[] ret = new String[3];
    try {
      MP3File mp3 = new MP3File(file);
      String mtitle = null, martist=null, malbum=null;
      if(mp3.hasID3v1Tag()) {
        mtitle = mp3.getID3v1Tag().getTitle();
        martist = mp3.getID3v1Tag().getArtist();
        malbum = mp3.getID3v1Tag().getAlbum();
      } else if(mp3.hasID3v2Tag()) {
        mtitle = mp3.getID3v2Tag().getSongTitle();
        martist = mp3.getID3v2Tag().getLeadArtist();
        malbum = mp3.getID3v2Tag().getAlbumTitle();
      }
      ret[0] = toUTF8(martist);
      ret[1] = toUTF8(malbum); 
      ret[2] = toUTF8(mtitle);
    } catch (Exception e) {

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com.jitcaforwin.id3.jid3lib.TagFactoryTest

com.jitcaforwin.id3.jid3lib.TagGenreTest

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com.main.gui.JMP3Propriedades

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