| 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”来补充。另外Genre是个例外，它用一个字节表示歌曲流派，其对应表如下(由于该内容太多，只列出前50项)：
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：
1 Public Class Mp3Info
2
3
4
5 Private Const TAGLEN As Integer = 128
6
7
8
9 Private _MP3Tag As String = String.Empty
10
11 Private _Artist As String = String.Empty
12
13 Private _Title As String = String.Empty
14
15 Private _Album As String = String.Empty
16
17 Private _Comment As String = String.Empty
18
19 Private _Year As String = String.Empty
20
21 Private _Genre As String = String.Empty
22
23 Private _GenreID As Byte
24
25
26
27 Private Genres() As String = {"Blues", "Classic Rock", "Country", "Dance", "Disco", "Funk", "Grunge", _
28
29 "Hip-Hop", "Jazz", "Metal", "New Age", "Oldies", "Other", "Pop", "R&B", "Rap", "Reggae", "Rock", _
30
31 "Techno", "Industrial", "Alternative", "Ska", "Death Metal", "Pranks", "Soundtrack", "Euro-Techno", _
32
33 "Ambient", "Trip-Hop", "Vocal", "Jazz+Funk", "Fusion", "Trance", "Classical", "Instrumental", "Acid", _
34
35 "House", "Game", "Sound Clip", "Gospel", "Noise", "AlternRock", "Bass", "Soul", "Punk", "Space", _
36
37 "Meditative", "Instrumental Pop", "Instrumental Rock", "Ethnic", "Gothic", "Darkwave", "Techno-Industrial", _
38
39 "Electronic", "Pop-Folk", "Eurodance", "Dream", "Southern Rock", "Comedy", "Cult", "Gangsta", "Top 40", _
40
41 "Christian Rap", "Pop/Funk", "Jungle", "Native American", "Cabaret", "New Wave", "Psychedelic", "Rave", _
42
43 "Showtunes", "Trailer", "Lo-Fi", "Tribal", "Acid Punk", "Acid Jazz", "Polka", "Retro", "Musical", _
44
45 "Rock & Roll", "Hard Rock", "Folk", "Folk/Rock", "National Folk", "Swing", "Bebob", "Latin", "Revival", _
46
47 "Celtic", "Bluegrass", "Avantgarde", "Gothic Rock", "Progressive Rock", "Psychedelic Rock", "Symphonic Rock", _
48
49 "Slow Rock", "Big Band", "Chorus", "Easy Listening", "Acoustic", "Humour", "Speech", "Chanson", "Opera", _
50
51 "Chamber Music", "Sonata", "Symphony", "Booty Bass", "Primus", "Porn Groove", "Satire", "Slow Jam", "Club", _
52
53 "Tango", "Samba", "Folklore"}
54
55
56
57 Public Property MP3Tag() As String
58
59 Get
60
61 Return _MP3Tag
62
63 End Get
64
65 Set(ByVal value As String)
66
67 _MP3Tag = value.Trim
68
69 End Set
70
71 End Property
72
73
74
75 Public Property Title() As String
76
77 Get
78
79 Return _Title
80
81 End Get
82
83 Set(ByVal value As String)
84
85 _Title = value.Trim
86
87 End Set
88
89 End Property
90
91
92
93 Public Property Artist() As String
94
95 Get
96
97 Return _Artist
98
99 End Get
100
101 Set(ByVal value As String)
102
103 _Artist = value.Trim
104
105 End Set
106
107 End Property
108
109
110
111 Public Property Album() As String
112
113 Get
114
115 Return _Album
116
117 End Get
118
119 Set(ByVal value As String)
120
121 _Album = value.Trim
122
123 End Set
124
125 End Property
126
127
128
129 Public Property Comment() As String
130
131 Get
132
133 Return _Comment
134
135 End Get
136
137 Set(ByVal value As String)
138
139 _Comment = value.Trim
140
141 End Set
142
143 End Property
144
145
146
147 Public Property Genre() As String
148
149 Get
150
151 Return _Genre
152
153 End Get
154
155 Set(ByVal value As String)
156
157 _Genre = value.Trim
158
159 End Set
160
161 End Property
162
163
164
165 Public Property GenreID() As Byte
166
167 Get
168
169 Return _GenreID
170
171 End Get
172
173 Set(ByVal value As Byte)
174
175 _GenreID = value
176
177 End Set
178
179 End Property
180
181
182
183 Public Property Year() As String
184
185 Get
186
187 Return _Year
188
189 End Get
190
191 Set(ByVal value As String)
192
193 _Year = value.Trim
194
195 End Set
196
197 End Property
198
199 End Class
200
201
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：
204
205
206
207 Public Function GetMp3FileInfo(ByVal fname As String) As Boolean
208
209
210
211 'Open the filestream
212
213 Dim msfile As FileStream
214
215 Try
216
217 msfile = New FileStream(fname, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)
218
219 If Not (msfile.CanRead) Then
220
221 Throw New IO.IOException("无法读取文件:" + fname)
222
223 End If
224
225 Catch Ex As Exception
226
227 Throw New IO.IOException("读取文件发生错误！" + Ex.Message)
228
229 End Try
230
231
232
233 Dim ID3(TAGLEN - 1) As Byte
234
235 Dim BinReader As BinaryReader
236
237 Dim StrInfo As String
238
239
240
241 '使用BinaryReader来读取信息
242
243 BinReader = New BinaryReader(msfile)
244
245
246
247 msfile.Position = 0
248
249 msfile.Seek(-TAGLEN, SeekOrigin.End)
250
251
252
253 StrInfo = CBytesToString(BinReader.ReadBytes(3))
254
255
256
257 '判断标签头是否为 TAG
258
259 If StrInfo.ToUpper = "TAG" Then
260
261
262
263 '读取标题信息
264
265 StrInfo = CBytesToString(BinReader.ReadBytes(30)).Replace(Chr(0), "")
266
267 _Title = StrInfo
268
269
270
271 '读取艺术家信息
272
273 StrInfo = CBytesToString(BinReader.ReadBytes(30)).Replace(Chr(0), "")
274
275 _Artist = StrInfo
276
277
278
279 '读取专辑信息
280
281 StrInfo = CBytesToString(BinReader.ReadBytes(30)).Replace(Chr(0), "")
282
283 _Album = StrInfo
284
285
286
287 '读取出版年度信息
288
289 StrInfo = CBytesToString(BinReader.ReadBytes(4)).Replace(Chr(0), "")
290
291 _Year = StrInfo
292
293
294
295 '读取备注信息
296
297 StrInfo = CBytesToString(BinReader.ReadBytes(30)).Replace(Chr(0), "")
298
299 _Comment = StrInfo
300
301
302
303 '读取歌曲流派信息
304
305 _GenreID = BinReader.ReadByte
306
307
308
309 End If
310
311
312
313 BinReader.Close()
314
315 msfile.Close()
316
317
318
319 End Function
320
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
326
327 '注意这里 需要对编码进行处理, 防止出现乱码
328
329 Dim GbCode As Encoding = Encoding.GetEncoding("gb2312")
330
331 If Bytes.Length > 0 Then
332
333 Return GbCode.GetString(Bytes)
334
335 Else
336
337 Return String.Empty
338
339 End If
340
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：
1 Module Module1
2
3
4
5 Sub
6
7
8
9 Dim Mp3 As New Mp3Info("D:\Music\Top 40 Singles\39 Embrace - Natures Law.mp3")
10
11
12
13 Console.WriteLine("Title : " + Mp3.Title)
14
15 Console.WriteLine("Artist: " + Mp3.Artist)
16
17 Console.WriteLine("Album : " + Mp3.Album)
18
19 Console.Read()
20
21 End Sub
22
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。
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