framebodyaspi.java

java+eclipse做的TTPlayer

/*
 *  MusicTag Copyright (C)2003,2004
 *
 *  This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser
 *  General Public  License as published by the Free Software Foundation; either version 2.1 of the License,
 *  or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
 *  the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *  See the GNU Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License along with this library; if not,
 *  you can get a copy from http://www.opensource.org/licenses/lgpl-license.php or write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package com.hadeslee.audiotag.tag.id3.framebody;

import com.hadeslee.audiotag.tag.InvalidTagException;
import com.hadeslee.audiotag.tag.datatype.NumberFixedLength;
import com.hadeslee.audiotag.tag.datatype.NumberVariableLength;
import com.hadeslee.audiotag.tag.id3.ID3v24Frames;

import java.nio.ByteBuffer;

/**
 *  Audio files with variable bit rates are intrinsically difficult to
   deal with in the case of seeking within the file. The ASPI frame
   makes seeking easier by providing a list a seek points within the
   audio file. The seek points are a fractional offset within the audio
   data, providing a starting point from which to find an appropriate
   point to start decoding. The presence of an ASPI frame requires the
   existence of a TLEN frame, indicating the duration of the file in
   milliseconds. There may only be one 'audio seek point index' frame in
   a tag.

     <Header for 'Seek Point Index', ID: "ASPI">
     Indexed data start (S)         $xx xx xx xx
     Indexed data length (L)        $xx xx xx xx
     Number of index points (N)     $xx xx
     Bits per index point (b)       $xx

   Then for every index point the following data is included;

     Fraction at index (Fi)          $xx (xx)

   'Indexed data start' is a byte offset from the beginning of the file.
   'Indexed data length' is the byte length of the audio data being
   indexed. 'Number of index points' is the number of index points, as
   the name implies. The recommended number is 100. 'Bits per index
   point' is 8 or 16, depending on the chosen precision. 8 bits works
   well for short files (less than 5 minutes of audio), while 16 bits is
   advantageous for long files. 'Fraction at index' is the numerator of
   the fraction representing a relative position in the data. The
   denominator is 2 to the power of b.

   Here are the algorithms to be used in the calculation. The known data
   must be the offset of the start of the indexed data (S), the offset
   of the end of the indexed data (E), the number of index points (N),
   the offset at index i (Oi). We calculate the fraction at index i
   (Fi).

   Oi is the offset of the frame whose start is soonest after the point
   for which the time offset is (i/N * duration).

   The frame data should be calculated as follows:

     Fi = Oi/L * 2^b    (rounded down to the nearest integer)

   Offset calculation should be calculated as follows from data in the
   frame:

     Oi = (Fi/2^b)*L    (rounded up to the nearest integer)

 * @author : Paul Taylor
 * @author : Eric Farng
 * @version $Id: FrameBodyASPI.java,v 1.13 2007/08/06 16:04:34 paultaylor Exp $
 */
public class FrameBodyASPI extends AbstractID3v2FrameBody implements ID3v24FrameBody
{
    private static final int DATA_START_FIELD_SIZE = 4;
    private static final int DATA_LENGTH_FIELD_SIZE = 4;
    private static final int NO_OF_INDEX_POINTS_FIELD_SIZE = 2;
    private static final int BITS_PER_INDEX_POINTS_FIELD_SIZE = 1;
    private static final int FRACTION_AT_INDEX_MINIMUM_FIELD_SIZE = 1;
    private static final String INDEXED_DATA_START = "IndexedDataStart";
    private static final String INDEXED_DATA_LENGTH = "IndexedDataLength";
    private static final String NUMBER_OF_INDEX_POINTS = "NumberOfIndexPoints";
    private static final String BITS_PER_INDEX_POINT = "BitsPerIndexPoint";
    private static final String FRACTION_AT_INDEX = "FractionAtIndex";

    /**
     * Creates a new FrameBodyASPI datatype.
     */
    public FrameBodyASPI()
    {
    }

    /**
     * Creates a new FrameBodyASPI from another FrameBodyASPI
     * @param copyObject
     */
    public FrameBodyASPI(FrameBodyASPI copyObject)
    {
        super(copyObject);
    }

    /**
     * Creates a new FrameBodyASPI datatype.          

     * @throws InvalidTagException 
     */
    public FrameBodyASPI(ByteBuffer byteBuffer, int frameSize)
        throws InvalidTagException
    {
        super(byteBuffer, frameSize);
    }

      /**
      * The ID3v2 frame identifier
      *
      * @return the ID3v2 frame identifier  for this frame type
     */
    public String getIdentifier()
    {
        return ID3v24Frames.FRAME_ID_AUDIO_SEEK_POINT_INDEX;
    }


    protected void setupObjectList()
    {
        objectList.add(new NumberFixedLength(INDEXED_DATA_START,this,DATA_START_FIELD_SIZE));
        objectList.add(new NumberFixedLength(INDEXED_DATA_LENGTH,this,DATA_LENGTH_FIELD_SIZE));
        objectList.add(new NumberFixedLength(NUMBER_OF_INDEX_POINTS,this,NO_OF_INDEX_POINTS_FIELD_SIZE));
        objectList.add(new NumberFixedLength(BITS_PER_INDEX_POINT,this,BITS_PER_INDEX_POINTS_FIELD_SIZE));
        objectList.add(new NumberVariableLength(FRACTION_AT_INDEX,this,FRACTION_AT_INDEX_MINIMUM_FIELD_SIZE ));
    }
}