读取MP3文件的ID3v1信息
前段时间，在局域网里面做一个小网站，其中有板块是涉及音乐的在线播放。考虑到以后维护的方便，决定把mp3文件都按专辑分不同的目录存放。然后使用一个程序监控存放mp3的目录，把每个mp3文件的信息都存入数据库中，用过ASP.NET页面将mp3文件的信息呈现给用户。其中使用.NET来读取mp3 文件的信息虽然不难，但也需要不少技巧，故将该过程整理与大家分享。
首先我们来看看mp3歌曲的信息所存放的位置。Mp3文件包含一个叫做ID3的标签。其实有两个标签，一个叫做ID3v1，另外一个叫做ID3v2。为了讲述的简单起见，我们这里只介绍ID3v1。
ID3V1结构比较简单，存放在MP3文件的末尾，大家可以用16进制的编辑器（例如：UltraEdit）打开一个MP3文件，注意其末尾的128个字节，数据结构定义如下：
名称 位置 长度 内容
Header 1-3 3 标签头
Title 4-33 30 标题
Artist 34-63 30 艺术家
Album 64-93 30 专辑
Year 94-97 4 出品年代
Comment 98-127 30 备注
Cenre 128 1 类型
注意：上述的标签头必须是”TAG”, 否则表示没有标签
ID3v1的各项信息是按顺序依次存放的，每项信息之后并没有任何的结束标志，如果某项信息长度小于标准长度，使用”\
0="Blues"
1="ClassicRock"
2="Country"
3="Dance"
4="Disco"
5="Funk"
6="Grunge"
7="Hip-Hop"
8="Jazz"
9="Metal"
10="NewAge"
11="Oldies"
12="Other"
13="Pop"
14="R&B"
15="Rap"
16="Reggae"
17="Rock"
18="Techno"
19="Industrial"
20="Alternative"
21="Ska"
22="DeathMetal"
23="Pranks"
24="Soundtrack"
25="Euro-Techno"
26="Ambient"
27="Trip-Hop"
28="Vocal"
29="Jazz+Funk"
30="Fusion"
31="Trance"
32="Classical"
33="Instrumental"
34="Acid"
35="House"
36="Game"
37="SoundClip"
38="Gospel"
39="Noise"
40="AlternRock"
41="Bass"
42="Soul"
43="Punk"
44="Space"
45="Meditative"
46="InstrumentalPop"
47="InstrumentalRock"
48="Ethnic"
49="Gothic"
50="Darkwave"
知道了MP3歌曲信息存放的结构之后，我们就可以写出对应的代码。
首先定一个MP3Info类：
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3
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5 Private Const TAGLEN As Integer = 128
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7
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9 Private _MP3Tag As String = String.Empty
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11 Private _Artist As String = String.Empty
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13 Private _Title As String = String.Empty
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15 Private _Album As String = String.Empty
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17 Private _Comment As String = String.Empty
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19 Private _Year As String = String.Empty
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21 Private _Genre As String = String.Empty
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23 Private _GenreID As Byte
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25
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27 Private Genres() As String = {"Blues", "Classic Rock", "Country", "Dance", "Disco", "Funk", "Grunge", _
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29 "Hip-Hop", "Jazz", "Metal", "New Age", "Oldies", "Other", "Pop", "R&B", "Rap", "Reggae", "Rock", _
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31 "Techno", "Industrial", "Alternative", "Ska", "Death Metal", "Pranks", "Soundtrack", "Euro-Techno", _
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33 "Ambient", "Trip-Hop", "Vocal", "Jazz+Funk", "Fusion", "Trance", "Classical", "Instrumental", "Acid", _
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35 "House", "Game", "Sound Clip", "Gospel", "Noise", "AlternRock", "Bass", "Soul", "Punk", "Space", _
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37 "Meditative", "Instrumental Pop", "Instrumental Rock", "Ethnic", "Gothic", "Darkwave", "Techno-Industrial", _
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39 "Electronic", "Pop-Folk", "Eurodance", "Dream", "Southern Rock", "Comedy", "Cult", "Gangsta", "Top 40", _
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41 "Christian Rap", "Pop/Funk", "Jungle", "Native American", "Cabaret", "New Wave", "Psychedelic", "Rave", _
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43 "Showtunes", "Trailer", "Lo-Fi", "Tribal", "Acid Punk", "Acid Jazz", "Polka", "Retro", "Musical", _
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45 "Rock & Roll", "Hard Rock", "Folk", "Folk/Rock", "National Folk", "Swing", "Bebob", "Latin", "Revival", _
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47 "Celtic", "Bluegrass", "Avantgarde", "Gothic Rock", "Progressive Rock", "Psychedelic Rock", "Symphonic Rock", _
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49 "Slow Rock", "Big Band", "Chorus", "Easy Listening", "Acoustic", "Humour", "Speech", "Chanson", "Opera", _
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51 "Chamber Music", "Sonata", "Symphony", "Booty Bass", "Primus", "Porn Groove", "Satire", "Slow Jam", "Club", _
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53 "Tango", "Samba", "Folklore"}
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55
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57 Public Property MP3Tag() As String
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59 Get
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61 Return _MP3Tag
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63 End Get
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65 Set(ByVal value As String)
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67 _MP3Tag = value.Trim
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69 End Set
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71 End Property
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75 Public Property Title() As String
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77 Get
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79 Return _Title
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81 End Get
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83 Set(ByVal value As String)
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85 _Title = value.Trim
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87 End Set
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89 End Property
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93 Public Property Artist() As String
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95 Get
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97 Return _Artist
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99 End Get
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101 Set(ByVal value As String)
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103 _Artist = value.Trim
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105 End Set
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107 End Property
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111 Public Property Album() As String
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113 Get
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115 Return _Album
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117 End Get
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119 Set(ByVal value As String)
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121 _Album = value.Trim
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123 End Set
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125 End Property
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129 Public Property Comment() As String
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131 Get
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133 Return _Comment
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135 End Get
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137 Set(ByVal value As String)
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139 _Comment = value.Trim
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141 End Set
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143 End Property
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147 Public Property Genre() As String
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149 Get
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151 Return _Genre
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153 End Get
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155 Set(ByVal value As String)
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157 _Genre = value.Trim
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159 End Set
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161 End Property
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165 Public Property GenreID() As Byte
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167 Get
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169 Return _GenreID
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171 End Get
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173 Set(ByVal value As Byte)
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175 _GenreID = value
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177 End Set
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179 End Property
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183 Public Property Year() As String
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185 Get
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187 Return _Year
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189 End Get
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191 Set(ByVal value As String)
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193 _Year = value.Trim
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195 End Set
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197 End Property
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199 End Class
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202
203 上面的类只包含了mp3歌曲信息对应的数据结构，我们还要为它添加具体读取mp3文件信息的过程：
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207 Public Function GetMp3FileInfo(ByVal fname As String) As Boolean
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209
210
211 'Open the filestream
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213 Dim msfile As FileStream
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215 Try
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217 msfile = New FileStream(fname, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)
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219 If Not (msfile.CanRead) Then
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221 Throw New IO.IOException("无法读取文件:" + fname)
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223 End If
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225 Catch Ex As Exception
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227 Throw New IO.IOException("读取文件发生错误！" + Ex.Message)
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229 End Try
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231
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233 Dim ID3(TAGLEN - 1) As Byte
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235 Dim BinReader As BinaryReader
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237 Dim StrInfo As String
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239
240
241 '使用BinaryReader来读取信息
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243 BinReader = New BinaryReader(msfile)
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245
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247 msfile.Position = 0
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249 msfile.Seek(-TAGLEN, SeekOrigin.End)
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251
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253 StrInfo = CBytesToString(BinReader.ReadBytes(3))
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255
256
257 '判断标签头是否为 TAG
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259 If StrInfo.ToUpper = "TAG" Then
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261
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263 '读取标题信息
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265 StrInfo = CBytesToString(BinReader.ReadBytes(30)).Replace(Chr(0), "")
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267 _Title = StrInfo
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269
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271 '读取艺术家信息
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273 StrInfo = CBytesToString(BinReader.ReadBytes(30)).Replace(Chr(0), "")
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275 _Artist = StrInfo
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277
278
279 '读取专辑信息
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281 StrInfo = CBytesToString(BinReader.ReadBytes(30)).Replace(Chr(0), "")
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283 _Album = StrInfo
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285
286
287 '读取出版年度信息
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289 StrInfo = CBytesToString(BinReader.ReadBytes(4)).Replace(Chr(0), "")
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291 _Year = StrInfo
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293
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295 '读取备注信息
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297 StrInfo = CBytesToString(BinReader.ReadBytes(30)).Replace(Chr(0), "")
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299 _Comment = StrInfo
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301
302
303 '读取歌曲流派信息
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305 _GenreID = BinReader.ReadByte
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307
308
309 End If
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311
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313 BinReader.Close()
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315 msfile.Close()
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317
318
319 End Function
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321
322
323 '用于转换编码, 防止出现中文乱码
324
325 Private Function CBytesToString(ByVal Bytes() As Byte) As String
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327 '注意这里 需要对编码进行处理, 防止出现乱码
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329 Dim GbCode As Encoding = Encoding.GetEncoding("gb2312")
330
331 If Bytes.Length > 0 Then
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333 Return GbCode.GetString(Bytes)
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335 Else
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337 Return String.Empty
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339 End If
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341 End Function
我们可以用一个简单的Console程序来说明，如何使用Mp3Info类。使用Visual Studio 2005 Express，创建一个Console程序：
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3
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5 Sub
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9 Dim Mp3 As New Mp3Info("D:\Music\Top 40 Singles\39 Embrace - Natures Law.mp3")
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11
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13 Console.WriteLine("Title : " + Mp3.Title)
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15 Console.WriteLine("Artist: " + Mp3.Artist)
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17 Console.WriteLine("Album : " + Mp3.Album)
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19 Console.Read()
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21 End Sub
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23
24 End Module
运行该程序后输出为：
Title : Nature's Law
Artist: Embrace
Album : DHZ.INC
Genre : Blues
本文只针对mp3的ID3v1进行了讨论，而实际上很多mp3不仅仅包含ID3v1的信息，还包含ID3v2的信息。
但ID3v2要比ID3v1复杂，对于ID3v2的处理，要等下次有空的时候再写了。
