Examples of org.farng.mp3.MP3File

org.farng.mp3.InvalidTagException

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 display()
    {
  clear();


  try { 
      MP3File m = new MP3File(getFile());
      
      jtAlbum.setText(m.getAlbum());
      jtArtist.setText(m.getArtist());
      jtTitle.setText(m.getTitle());
      jtYear.setText(m.getYear());
      jtComment.setText(m.getComment());


      // why call getFile().canRead()? an IOException should have
      // occured if we could not read the file
      setEnabled(getFile().canWrite());
  }

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     * Writes id3 tags to file.
     */
    protected void save()
    {
  try {
      MP3File m = new MP3File(getFile());


      m.setTitle(jtTitle.getText());
      m.setArtist(jtArtist.getText());
      m.setAlbum(jtAlbum.getText());
      m.setYear(jtYear.getText());
      m.setComment(jtComment.getText());


      m.writeTags();


      setStatus(XNap.tr("Changes successfully saved."));
  }
  catch (Exception e) {
      setStatus(XNap.tr("Could not write ID Tags to file"));

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    this.fileName = file.getName();
    File sub = oneUp(file);
    this.subDirectory = sub.getName();
    this.rootDirectory = oneUp(sub).getName();


    MP3File mp3File = new MP3File(file);
    try {
      tag1 = mp3File.getID3V1Tag();
      if(tag1==null){
        tag1 = new ID3V1_0Tag();
      }
    } catch (ID3Exception e) {
      tag1 = new ID3V1_0Tag();

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    return nullGuard(parameters.get("full"));


  }


  public void persist(String directory) {
    MP3File mp3File = new MP3File(new File(directory + getFull()));
    ID3V1Tag tag1 = null;
    try {
      tag1 = mp3File.getID3V1Tag();
      if(tag1==null){
        tag1 = new ID3V1_0Tag();
      }
    } catch (ID3Exception e) {
      tag1 = new ID3V1_0Tag();
    }
    if(!"".equals(getTitle())) tag1.setTitle(getTitle());
    tag1.setAlbum(getAlbum());
    tag1.setArtist(getArtist());
    tag1.setComment(getComment());
    try {
      tag1.setGenre(Genre.lookupGenre(getGenre()));
    } catch (ID3Exception e) {
    }
    tag1.setYear(getYear());
    mp3File.setID3Tag(tag1);
    try {
      mp3File.sync();
    } catch (ID3Exception e) {
    }
  }

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   * Construst a SongData from an MP3 at the given absolute path
   * @param path the absolute path of the MP3
   */
  public SongData( String path ) throws SongDataException {
    this.path = tagPrep(path);
    AbstractMP3Tag tag = null;
        try {
      MP3File mp3file = new MP3File(path);
      if (mp3file.hasID3v2Tag()) {
        tag = mp3file.getID3v2Tag();
      } else if (mp3file.hasID3v1Tag()) {
        tag = mp3file.getID3v1Tag();
      } else {
        throw new SongDataException( "No MP3 ID tag found for \""+path+"\"" );
      }
        } catch (TagException tE) {
            throw new SongDataException( "(TagException) Broken MP3 ID tag found for \""+path+"\"" );
        } catch (IOException ioE) {
            log.warn("", ioE);
            throw new SongDataException( "IOE for \""+path+"\"" );
    }


    try { //unfortunately jd3lib isn't perfect...grr...
      title = tagPrep(tag.getSongTitle());
      album = tagPrep(tag.getAlbumTitle());
      artist = tagPrep(tag.getLeadArtist());
            genre = tagPrep(tag.getSongGenre());
            if (genre.length() > 1) { // ensure that genres do not have mutiples because of case
                char firstChar = genre.toUpperCase().charAt(0);
                genre = firstChar+genre.substring(1);
            }
            track = Integer.parseInt(tag.getTrackNumberOnAlbum());


        } catch (NullPointerException npE) {
      throw new SongDataException( "(NPE) Broken MP3 ID tag found for \""+path+"\"" );
    } catch (NumberFormatException nfE) {
            log.warn("No track number for " + title);

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        // read the 5 character size
        file.read(buffer, 0, 5);
        final int size = Integer.parseInt(new String(buffer, 0, 5));
        if ((size == 0) && (TagOptionSingleton.getInstance().isLyrics3KeepEmptyFieldIfRead() == false)) {
            throw new InvalidTagException("Lyircs3v2 Field has size of zero.");
        }
        buffer = new byte[size];


        // read the SIZE length description
        file.read(buffer);

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        // read the 5 character size
        file.read(buffer, 0, 5);
        final int size = Integer.parseInt(new String(buffer, 0, 5));
        if ((size == 0) && (TagOptionSingleton.getInstance().isLyrics3KeepEmptyFieldIfRead() == false)) {
            throw new InvalidTagException("Lyircs3v2 Field has size of zero.");
        }
        buffer = new byte[size];


        // read the SIZE length description
        file.read(buffer);

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        final String identifier = new String(buffer, 0, 4);


        // is this a valid identifier?
        if (isValidID3v2FrameIdentifier(identifier) == false) {
            file.seek(file.getFilePointer() - 3);
            throw new InvalidTagException(identifier + " is not a valid ID3v2.30 frame");
        }
        filePointer = file.getFilePointer();


        // skip the 4 byte size
        file.skipBytes(4);

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        // read the 5 character size
        file.read(buffer, 0, 5);
        final int size = Integer.parseInt(new String(buffer, 0, 5));
        if ((size == 0) && (TagOptionSingleton.getInstance().isLyrics3KeepEmptyFieldIfRead() == false)) {
            throw new InvalidTagException("Lyircs3v2 Field has size of zero.");
        }
        buffer = new byte[size];


        // read the SIZE length description
        file.read(buffer);

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        // read the 5 character size
        file.read(buffer, 0, 5);
        final int size = Integer.parseInt(new String(buffer, 0, 5));
        if ((size == 0) && (TagOptionSingleton.getInstance().isLyrics3KeepEmptyFieldIfRead() == false)) {
            throw new InvalidTagException("Lyircs3v2 Field has size of zero.");
        }
        buffer = new byte[size];


        // read the SIZE length description
        file.read(buffer);

View Full Code Here

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Related Classes of org.farng.mp3.MP3File

com.jitcaforwin.id3.jid3lib.TagFactoryTest

com.jitcaforwin.id3.jid3lib.TagGenreTest

com.jitcaforwin.id3.jid3lib.TagTestHelpLibrary

com.main.gui.JMP3Propriedades

junit.framework.TestSuite

net.nutch.parse.mp3.MP3Parser

org.apache.nutch.parse.mp3.MP3Parser

org.farng.mp3.AbstractMP3FragmentBody

org.farng.mp3.AbstractMP3Tag

org.farng.mp3.filename.FilenameTag

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