1 | package org.farng.mp3.id3; |
2 | |
3 | import org.farng.mp3.InvalidTagException; |
4 | |
5 | import java.io.IOException; |
6 | import java.io.RandomAccessFile; |
7 | |
8 | /** |
9 | * <h3>4.30. Audio seek point index</h3> |
10 | * <p/> |
11 | * <p> Audio files with variable bit rates are intrinsically difficult to<br> deal with in the |
12 | * case of seeking within the file. The ASPI frame<br> makes seeking easier by providing a list a seek |
13 | * points within the<br> audio file. The seek points are a fractional offset within the audio<br> |
14 | * data, providing a starting point from which to find an appropriate<br> |
15 | * <p/> |
16 | * point to start decoding. The presence of an ASPI frame requires the<br> existence of a TLEN |
17 | * frame, indicating the duration of the file in<br> milliseconds. There may only be one 'audio seek point |
18 | * index' frame in<br> a tag.</p> |
19 | * <p/> |
20 | * <p> <Header for 'Seek Point Index', ID: "ASPI"><br> |
21 | * Indexed data start (S) $xx xx xx xx<br> |
22 | * Indexed data length (L) $xx xx xx xx<br> Number of |
23 | * index points (N) $xx xx<br> |
24 | * <p/> |
25 | * Bits per index point (b) $xx</p> |
26 | * <p/> |
27 | * <p> Then for every index point the following data is included;</p> |
28 | * <p/> |
29 | * <p> Fraction at index (Fi) $xx |
30 | * (xx)</p> |
31 | * <p/> |
32 | * <p> 'Indexed data start' is a byte offset from the beginning of the file.<br> 'Indexed data |
33 | * length' is the byte length of the audio data being<br> indexed. 'Number of index points' is the number |
34 | * of index points, as<br> the name implies. The recommended number is 100. 'Bits per index<br> |
35 | * point' is 8 or 16, depending on the chosen precision. 8 bits works<br> |
36 | * <p/> |
37 | * well for short files (less than 5 minutes of audio), while 16 bits is<br> advantageous for |
38 | * long files. 'Fraction at index' is the numerator of<br> the fraction representing a relative position in |
39 | * the data. The<br> denominator is 2 to the power of b.</p> |
40 | * <p/> |
41 | * <p> Here are the algorithms to be used in the calculation. The known data<br> must be the |
42 | * offset of the start of the indexed data (S), the offset<br> of the end of the indexed data (E), the |
43 | * number of index points (N),<br> the offset at index i (Oi). We calculate the fraction at index i<br> |
44 | * (Fi).</p> |
45 | * <p/> |
46 | * <p> Oi is the offset of the frame whose start is soonest after the point<br> for which the |
47 | * time offset is (i/N * duration).</p> |
48 | * <p/> |
49 | * <p> The frame data should be calculated as follows:</p> |
50 | * <p/> |
51 | * <p> Fi = Oi/L * 2^b (rounded down to the nearest integer)</p> |
52 | * <p/> |
53 | * <p> Offset calculation should be calculated as follows from data in the<br> frame:</p> |
54 | * <p/> |
55 | * <p> Oi = (Fi/2^b)*L (rounded up to the nearest integer)<br> </p> |
56 | * |
57 | * @author Eric Farng |
58 | * @version $Revision: 1.5 $ |
59 | */ |
60 | public class FrameBodyASPI extends AbstractID3v2FrameBody { |
61 | |
62 | private short[] fraction = null; |
63 | private int bitsPerPoint = 0; |
64 | private int dataLength = 0; |
65 | private int dataStart = 0; |
66 | private int indexPoints = 0; |
67 | |
68 | /** |
69 | * Creates a new FrameBodyASPI object. |
70 | */ |
71 | public FrameBodyASPI() { |
72 | super(); |
73 | } |
74 | |
75 | /** |
76 | * Creates a new FrameBodyASPI object. |
77 | */ |
78 | public FrameBodyASPI(final FrameBodyASPI copyObject) { |
79 | super(copyObject); |
80 | fraction = (short[]) copyObject.fraction.clone(); |
81 | bitsPerPoint = copyObject.bitsPerPoint; |
82 | dataLength = copyObject.dataLength; |
83 | dataStart = copyObject.dataStart; |
84 | indexPoints = copyObject.indexPoints; |
85 | } |
86 | |
87 | /** |
88 | * Creates a new FrameBodyASPI object. |
89 | */ |
90 | public FrameBodyASPI(final int dataStart, |
91 | final int dataLength, |
92 | final int indexPoints, |
93 | final int bitsPerPoint, |
94 | final short[] fraction) { |
95 | super(); |
96 | this.dataStart = dataStart; |
97 | this.dataLength = dataLength; |
98 | this.indexPoints = indexPoints; |
99 | this.bitsPerPoint = bitsPerPoint; |
100 | this.fraction = new short[fraction.length]; |
101 | System.arraycopy(fraction, 0, this.fraction, 0, fraction.length); |
102 | } |
103 | |
104 | /** |
105 | * Creates a new FrameBodyASPI object. |
106 | */ |
107 | public FrameBodyASPI(final RandomAccessFile file) throws IOException, InvalidTagException { |
108 | super(); |
109 | read(file); |
110 | } |
111 | |
112 | public String getIdentifier() { |
113 | return "ASPI"; |
114 | } |
115 | |
116 | public int getSize() { |
117 | return 4 + 4 + 2 + 1 + fraction.length << 1; |
118 | } |
119 | |
120 | /** |
121 | * This method is not yet supported. |
122 | * |
123 | * @throws UnsupportedOperationException This method is not yet supported |
124 | */ |
125 | public void equals() { |
126 | // todo Implement this java.lang.Object method |
127 | throw new UnsupportedOperationException("Method equals() not yet implemented."); |
128 | } |
129 | |
130 | protected void setupObjectList() { |
131 | // throw new UnsupportedOperationException(); |
132 | } |
133 | |
134 | public void read(final RandomAccessFile file) throws IOException, InvalidTagException { |
135 | final int size = readHeader(file); |
136 | if (size == 0) { |
137 | throw new InvalidTagException("Empty Frame"); |
138 | } |
139 | dataStart = file.readInt(); |
140 | dataLength = file.readInt(); |
141 | indexPoints = (int) file.readShort(); |
142 | bitsPerPoint = (int) file.readByte(); |
143 | fraction = new short[indexPoints]; |
144 | for (int i = 0; i < indexPoints; i++) { |
145 | if (bitsPerPoint == 8) { |
146 | fraction[i] = (short) file.readByte(); |
147 | } else if (bitsPerPoint == 16) { |
148 | fraction[i] = file.readShort(); |
149 | } else { |
150 | throw new InvalidTagException("ASPI bits per point wasn't 8 or 16"); |
151 | } |
152 | } |
153 | } |
154 | |
155 | public String toString() { |
156 | return getIdentifier() + ' ' + this |
157 | .dataStart + ' ' + this |
158 | .dataLength + ' ' + this |
159 | .indexPoints + ' ' + this |
160 | .bitsPerPoint + ' ' + this.fraction |
161 | .toString(); |
162 | } |
163 | |
164 | public void write(final RandomAccessFile file) throws IOException { |
165 | writeHeader(file, getSize()); |
166 | file.writeInt(dataStart); |
167 | file.writeInt(dataLength); |
168 | file.writeShort(indexPoints); |
169 | file.writeByte(16); |
170 | for (int i = 0; i < indexPoints; i++) { |
171 | file.writeShort((int) fraction[i]); |
172 | } |
173 | } |
174 | } |