/*
* 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 org.jaudiotagger.tag.id3.framebody;
import org.jaudiotagger.tag.InvalidTagException;
import org.jaudiotagger.tag.datatype.NumberFixedLength;
import org.jaudiotagger.tag.datatype.NumberVariableLength;
import org.jaudiotagger.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.
* <p/>
* <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
* <p/>
* Then for every index point the following data is included;
* <p/>
* Fraction at index (Fi) $xx (xx)
* <p/>
* '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.
* <p/>
* 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).
* <p/>
* Oi is the offset of the frame whose start is soonest after the point
* for which the time offset is (i/N * duration).
* <p/>
* The frame data should be calculated as follows:
* <p/>
* Fi = Oi/L * 2^b (rounded down to the nearest integer)
* <p/>
* Offset calculation should be calculated as follows from data in the
* frame:
* <p/>
* Oi = (Fi/2^b)*L (rounded up to the nearest integer)
*
* @author : Paul Taylor
* @author : Eric Farng
* @version $Id: FrameBodyASPI.java 832 2009-11-12 13:25:38Z paultaylor $
*/
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.
*
* @param byteBuffer
* @param frameSize
* @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));
}
}