本来想写点进度控制与音量调整的代码的,后来发现还是太简单了,就是几个MCI命令,来回搬弄,自己都没兴趣写下去。所以我想还是写些独门一点的:音乐信息的读取! 目前常见的主流音乐格式就两种,MP3与WMA,它们都有在文件中保存音乐信息的特定格式,MP3使用的当然是家喻户晓的ID3格式,分为V1与V2两个版本;WMA是MS的宠儿,它只是ASF格式的一个分支,当然遵循ASF的包装规则。 怎么获取它们包含的音乐信息呢?一般是自己读取,当然XP系统开始提供了音乐文件的详细信息资料,利用FSO可以真接从系统那里读取到,这不在本文范围,毕竟不用控件更自由,通用性更好。所以,有必要去深入一下这几种音乐信息格式。还是用代码说话吧,先说说MP3的ID3V1与ID3V2的格式。 ID3V1很简单,共128个字节,写在文件尾部,格式如下: Private Type Mp3ID3V1 Header As String * 3 Title As String * 30 Artist As String * 30 Album As String * 30 Year As String * 4 Comment As String * 30 Genre As String * 1 End Type
ID3V2是后来出现的,可扩展性很强,写在文件头部,采用标签组格式,分两部分,一是标签组的总头部,一是每个子标签的头部,分别定义如下: Private Type Mp3ID3V2 Header As String * 3 Ver As Byte Revision As Byte Flag As Byte Size(3) As Byte End Type
Private Type Mp3ID3V2Tag Tag As String * 4 Size(3) As Byte Flag(1) As Byte End Type 为了组织音乐信息的方便,我还定义了一个自己的结构,以便于使用: '音乐类型 Private Enum MediaType mciMIDI = 1 mciMP3 = 2 mciASF = 4 mciVIDEO = 8 mciWAVE = 16 End Enum '装载音乐信息的结构 Private Type MusicInfo FileName As String MusicType As MediaType Title As String Artist As String Album As String Year As String Lyrics As String Writer As String Composer As String Bits As String Sample As String Length As Long End Type '我习惯于用代码说明问题,所以还是看看代码吧 Private Function GetMusicInfo(udtInfo As MusicInfo) As Boolean Dim strFileName As String, a() As String, i As Long With udtInfo strFileName = Dir(.FileName, vbNormal Or vbHidden Or vbReadOnly Or vbSystem Or vbArchive) If strFileName = vbNullString Then Exit Function .MusicType = GetMCIType(strFileName) If .MusicType And mciMP3 Then GetMusicInfo = GetMP3Info(udtInfo) ElseIf .MusicType And mciASF Then GetMusicInfo = GetASFInfo(udtInfo) End If End With End Function
Private Function GetMCIType(strFileName As String) As MediaType Dim ext As String If strFileName <> vbNullString Then ext = LCase$(Mid$(strFileName, InStrRev(strFileName, "."))) Select Case ext Case ".mpg", ".mpeg", ".avi", ".mpe", ".mpa", ".m1v", ".ifo", ".vob" GetMCIType = mciVIDEO Case ".mp3" GetMCIType = mciMP3 Case ".wav", ".snd", ".aif", ".au", ".aifc", ".aiff" GetMCIType = mciWAVE Case ".asf", ".wma", ".wm", ".wmd" GetMCIType = mciASF Case ".wmv" GetMCIType = mciASF Or mciVIDEO Case ".mid", ".midi", ".rmi" GetMCIType = mciMIDI End Select End If End Function Private Function GetMP3Info(udtInfo As MusicInfo) As Boolean Dim FreeNo As Long, n(1) As Byte, b() As Byte, TmpInfo As MusicInfo Dim Power As Long, v As Long, j As Long, Tagh As Mp3ID3V2Tag Dim id3 As Mp3ID3V1, s As String, Pos As Long, id32 As Mp3ID3V2 Dim sz As Long, s1 As String TmpInfo = udtInfo On Error GoTo exitg FreeNo = FreeFile Open TmpInfo.FileName For Binary As #FreeNo With TmpInfo Pos = LOF(FreeNo) - 127 If Pos > 0 Then Get #FreeNo, Pos, id3 If UCase$(id3.Header) = "TAG" Then s = Trim$(Replace$(id3.Title, vbNullChar, vbNullString)) If Len(s) > 0 Then s = Replace$(s, "-", vbNullString) s = Replace$(s, "——", vbNullString) s = Replace$(s, ".mp3", vbNullString, , , vbTextCompare) .Title = s End If s = Trim$(Replace$(id3.Artist, vbNullChar, vbNullString)) If Len(s) > 0 Then .Title = Replace$(.Title, s, vbNullString) .Artist = s End If s = Trim$(Replace$(id3.Album, vbNullChar, vbNullString)) If Len(s) > 0 Then .Album = s s = Trim$(Replace$(id3.Year, vbNullChar, vbNullString)) If Len(s) > 0 Then .Year = s End If End If Get #FreeNo, 1, id32 If id32.Header = "ID3" Then sz = (id32.Size(1) And &H7F) * &H400 + (id32.Size(2) And &H7F) * &H80 + (id32.Size(3) And &H7F) Pos = sz + 10 s1 = String(4, vbNullChar) Get #FreeNo, , Tagh Do While Not (Tagh.Tag = s1 Or Seek(FreeNo) > sz + 10) j = Tagh.Size(1) * &H10000 + Tagh.Size(2) * &H100 + Tagh.Size(3) If j > 0 Then ReDim b(j - 1) Get #FreeNo, , b s = StrConv(b, vbUnicode) s = Trim$(Replace$(s, vbNullChar, "")) Select Case Tagh.Tag Case "TIT2" .Title = s Case "TPE1" .Artist = s Case "TALB" .Album = s Case "TCOM" .Composer = s Case "TEXT" .Writer = s Case "TYER" .Year = s Case "USLT" s = Replace$(s, " ", " ") If LCase$(Left$(s, 3)) = "chi" Then .Lyrics = Mid$(s, 4) ElseIf LCase$(Left$(s, 3)) = "eng" Then .Lyrics = Mid$(s, 4) Else .Lyrics = s End If End Select End If Get #FreeNo, , Tagh Loop Else Pos = 1 End If Get #FreeNo, Pos, n sz = Pos If Not (n(0) = &HFF And n(1) >= &HFA And n(1) <= &HFF) Then Do While Not (n(0) = &HFF And n(1) = &HFB) Pos = Pos + 1 If Seek(FreeNo) - sz > 8192 Then GoTo exitg Get #FreeNo, Pos, n Loop End If Get #FreeNo, , n v = 0 For j = 4 To 7 Power = 2 ^ j If (n(0) And Power) = Power Then v = v + Power Next v = v \ 16 .Bits = Trim$(Mid$("144 320 32 48 56 64 80 96 112 128 160 192 224 256 320 ", v * 4 + 1, 4)) & "Kbps" v = 0 For j = 2 To 3 Power = 2 ^ j If (n(0) And Power) = Power Then v = v + Power Next v = v \ 4 .Sample = Trim$(Mid$("44 48 32 ?? ", v * 3 + 1, 3)) & "KHz" End With udtInfo = TmpInfo GetMP3Info = True exitg: Close #FreeNo End Function
还有个ASF格式,有点烦,下篇再做说明吧! 
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