private boolean tagExists(FileChannel fc) throws IOException {
    ByteBuffer b = ByteBuffer.allocate(3);
    fc.position(0);
    fc.read(b);
    String tagString = new String(b.array());

    return tagString.equals("ID3");
  }
  public RandomAccessFile delete(RandomAccessFile raf, RandomAccessFile tempRaf)
      throws IOException {
    FileChannel fc = raf.getChannel();
    fc.position(0);

    if (!tagExists(fc)) return raf;

    fc.position(6);

    ByteBuffer b = ByteBuffer.allocate(4);
    fc.read(b);
    b.rewind();

    int tagSize = (b.get() & 0xFF) << 21;
    tagSize += (b.get() & 0xFF) << 14;
    tagSize += (b.get() & 0xFF) << 7;
    tagSize += b.get() & 0xFF;

    FileChannel tempFC = tempRaf.getChannel();
    tempFC.position(0);

    fc.position(tagSize + 10);

    // Here we will try to skip eventual trash afer the tag and before the
    // audio data
    b = ByteBuffer.allocate(4);
    int skip = 0;
    while (fc.read(b) != -1) {
      if ((b.get(0) & 0xFF) == 0xFF
          && (b.get(1) & 0xE0) == 0xE0
          && (b.get(1) & 0x06) != 0
          && (b.get(2) & 0xF0) != 0xF0
          && (b.get(2) & 0x08) != 0x08) {
        fc.position(fc.position() - 4);
        break;
      }

      fc.position(fc.position() - 3);
      b.rewind();
      skip++;
    }

    tempFC.transferFrom(fc, 0, fc.size() - tagSize - 10 - skip);
    return tempRaf;
  }
  public void write(Tag tag, RandomAccessFile raf, RandomAccessFile tempRaf)
      throws CannotWriteException, IOException {
    FileChannel fc = raf.getChannel();

    int oldTagSize = 0;

    if (tagExists(fc)) {
      // read the length
      if (!canOverwrite(raf))
        throw new CannotWriteException("Overwritting of this kind of ID3v2 tag not supported yet");
      fc.position(6);

      ByteBuffer buf = ByteBuffer.allocate(4);
      fc.read(buf);
      oldTagSize = (buf.get(0) & 0xFF) << 21;
      oldTagSize += (buf.get(1) & 0xFF) << 14;
      oldTagSize += (buf.get(2) & 0xFF) << 7;
      oldTagSize += buf.get(3) & 0xFF;
      oldTagSize += 10;

      // System.err.println("Old tag size: "+oldTagSize);
      int newTagSize = tc.getTagLength(tag);

      if (oldTagSize >= newTagSize) {
        // replace
        // System.err.println("Old ID32v Tag found, replacing the old
        // tag");
        fc.position(0);

        fc.write(tc.convert(tag, oldTagSize - newTagSize));

        // ID3v2 Tag Written

        return;
      }
    }

    // create new tag with padding
    // System.err.println("Creating a new ID3v2 Tag");
    fc.position(oldTagSize);

    if (fc.size() > 15 * 1024 * 1024) {
      FileChannel tempFC = tempRaf.getChannel();

      tempFC.position(0);
      tempFC.write(tc.convert(tag, Id3v2TagCreator.DEFAULT_PADDING));
      tempFC.transferFrom(fc, tempFC.position(), fc.size() - oldTagSize);

      fc.close();
    } else {
      ByteBuffer[] content = new ByteBuffer[2];

      content[1] = ByteBuffer.allocate((int) fc.size());
      fc.read(content[1]);
      content[1].rewind();
      content[0] = tc.convert(tag, Id3v2TagCreator.DEFAULT_PADDING);
      fc.position(0);
      fc.write(content);
    }
  }