Visualizza wikitesto di Calcolare la potenza di picco e di ampiezza di un file WAV con le funzioni esterne del API di Libaudiofile

La libreria '''Libaudiofile''' consente la lettura e la scrittura di file audio in diversi formati comuni, astraendo i dettagli di formati di file e di formati di dati.

Per poter fruire in Gambas delle risorse di questa libreria, sarà necessario installare la libreria dinamica e condivisa: "''libaudiofile.so.1.0.0''"


Mostriamo di seguito un esempio per calcolare la potenza di picco e di ampiezza di un file WAV:
 Public Struct smooth
   buf As Float[]
   lungh As Integer
   start As Integer
   n As Integer
 End Struct
 
 
 Library "libaudiofile:1.0.0"
 
 Private Const AF_DEFAULT_TRACK As Integer = 1001
 Private Const AF_SAMPFMT_DOUBLE As Integer = 404
 
 <FONT Color=gray>' ''AFfilehandle afOpenFile (const char *filename, const char *mode, AFfilesetup setup)''
 ' ''Opens a specified audio file and creates a file handle structure.''</font>
 Private Extern afOpenFile(filename As String, mode As String, setup As Pointer) As Pointer
 
 <FONT Color=gray>' ''int afGetChannels (AFfilehandle, int track)''
 ' ''Get the number of interleaved track from an AFfilehandle structure for an audio track.''</font>
 Private Extern afGetChannels(AFfile As Pointer, track As Integer) As Integer
 
 <FONT Color=gray>' ''double afGetRate(AFfilehandle file, int track)''
 ' ''Get the track sample rate for a specified audio track from an AFfilehandle structure.''</font>
 Private Extern afGetRate(AFfile As Pointer, track As Integer) As Float
 
 <FONT Color=gray>' ''AFframecount afGetFrameCount (AFfilehandle file, int track)''
 ' ''Get the total sample frame count for a specified audio track from an AFfilehandle structure.''</font>
 Private Extern afGetFrameCount(AFfile As Pointer, track As Integer) As Long
 
 <FONT Color=gray>' ''int afSetVirtualSampleFormat (AFfilehandle, int track, int sampleFormat, int sampleWidth)''
 ' ''Set the virtual data format for a specified audio track.''</font>
 Private Extern afSetVirtualSampleFormat(AFfile As Pointer, track As Integer, sampleFormat As Integer, sampleWidth As Integer) As Integer
 
 <FONT Color=gray>' ''int afReadFrames (AFfilehandle, int track, void *buffer, int frameCount)''
 ' ''Read sample frames from a track in an audio file.''</font>
 Private Extern afReadFrames(AFfile As Pointer, track As Integer, buffer As Float[], frameCount As Integer) As Integer
 
 <FONT Color=gray>' ''int afCloseFile (AFfilehandle file)''
 ' ''Closes an open audio file, updating the file if it was opened for writing.''</font>
 Private Extern afCloseFile(AFfile As Pointer) As Integer
 
  
 '''Public''' Sub Main()
 
  Dim nomefile As String
  Dim fl As Pointer
  Dim canali, windowSize, frameCount As Integer
  Dim i, c, winStart, winEnd, fine As Integer
  Dim powsmooth As New Smooth[]
  Dim lastWindow As Boolean
  Dim frames, sums As Float[]
  Dim frequenza, sample, pow, maxpow, durata As Float
  Dim livello, picco, minSample, maxSample As Float
    
    
   nomefile = "<FONT Color=gray>''/percorso/del/file.wav''</font>"
   minSample = 1
   maxSample = -1
   
   fl = afOpenFile(nomefile, "r", 0)
   If IsNull(fl) Then Error.Raise("Impossibile aprire il file audio !")
    
   canali = afGetChannels(fl, AF_DEFAULT_TRACK)
   
   frequenza = afGetRate(fl, AF_DEFAULT_TRACK)
 
   durata = afGetFrameCount(fl, AF_DEFAULT_TRACK) / afGetRate(fl, AF_DEFAULT_TRACK)
 
   windowSize = CInt(frequenza / 100)
    
   frameCount = CInt(afGetFrameCount(fl, AF_DEFAULT_TRACK))
    
   afSetVirtualSampleFormat(fl, AF_DEFAULT_TRACK, AF_SAMPFMT_DOUBLE, SizeOf(gb.Float))
    
   powsmooth = New Smooth[canali]
 
   For c = 0 To canali - 1
     With powsmooth[c] = New Smooth
       .lungh = 100
       .buf = New Float[powsmooth[c].lungh * SizeOf(gb.Float)]
       .start = 0
       .n = 0
     End With
   Next
 
   Repeat
      
     winEnd = winStart + windowSize
     If winEnd >= frameCount Then 
       winEnd = frameCount
       lastWindow = True
     Endif
     frames = New Float[canali * windowSize]
     afReadFrames(fl, AF_DEFAULT_TRACK, frames, windowSize)
     sums = New Float[canali]
     For c = 0 To canali - 1
       sums[c] = 0
       For i = 0 To (winEnd - winStart) - 1
         sample = frames[i * canali + c]
         sums[c] += sample * sample
         If (sample > maxSample) Then maxSample = sample
         If (sample < minSample) Then minSample = sample
       Next
     Next
 
 <FONT Color=gray>' ''Calcola la potenza di ciascun canale:''</font>
     For c = 0 To canali - 1
       pow = sums[c] / (winEnd - winStart)
       fine = (powsmooth[c].start + powsmooth[c].n) % powsmooth[c].lungh
       powsmooth[c].buf[fine] = pow
       If powsmooth[c].n = powsmooth[c].lungh Then
         powsmooth[c].start = (powsmooth[c].start + 1) % powsmooth[c].lungh
         pow = Dati_Attenuati(powsmooth[c])
         If pow > maxpow Then maxpow = pow
       Else
         Inc powsmooth[c].n
       Endif
     Next
     winStart += windowSize
     
   Until lastWindow
    
   For c = 0 To canali - 1
     pow = Dati_Attenuati(powsmooth[c])
     If pow > maxpow Then maxpow = pow
   Next
    
   livello = Sqr(maxpow)
 
   afCloseFile(fl)
  
   Print "File audio: "; Null, nomefile
   Print "Frequenza: "; Null, "Hz ";frequenza
   Print "Canali: "; Null, canali
   Print "Durata: "; Null, Cstr(Date(0, 0, 0, 0, 0, 0, durata * 1000))
   Print "Livello (dB): "; Null, 20 * Log10(livello)
   Print "Picco-: "; Null, minSample
   Print "Picco+: "; Null, maxSample
    
   picco = Abs(minSample)
    
   If picco < Abs(maxSample) Then picco = Abs(maxSample)
    
   Print "Picco (dB): "; Null, 20 * Log10(picco)
  
 '''End'''
 
 
 '''Private''' Function Dati_Attenuati(s As Smooth) As Float
  
  Dim i As Integer
  Dim attenuato As Float
 
   attenuato = 0
   For i = 0 To s.n - 1
     attenuato += s.buf[i]
   Next
   attenuato = attenuato / s.n
 
   Return attenuato
  
 '''End'''




=Riferimenti=
* http://audiofile.68k.org/
* http://www.fifi.org/doc/libaudiofile-dev/