Visualizza wikitesto di Convertire un file di soli dati audio raw in un file di formato WAV con le funzioni esterne del API di Sndfile

E' possibile convertire un file contenente soli dati audio grezzi (''raw'') in un file audio di formato WAV con le funzioni esterne del API di Sndfile.
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E' necessario avere installata nel proprio sistema e richiamare in Gambas la libreria condivisa: "''libsndfile.so.1.0.31'' ".

Mostriamo un esempio pratico:
 Library "libsndfile:1.0.31"
 
 Public Struct SF_INFO
   frames As Long
   samplerate As Integer
   channels As Integer
   format_ As Integer
   sections As Integer
   seekable As Integer
 End Struct
 
 Private Const SF_FALSE As Integer = 0
 Private Const SFM_READ As Integer = &10
 Private Const SFM_WRITE As Integer = &20
 Private Const SF_FORMAT_WAV As Integer = &010000
 Private Const SF_FORMAT_PCM_16 As Integer = &02
 
 <FONT Color=gray>' ''SNDFILE * sf_open (const char *path, int mode, SF_INFO *sfinfo)''
 ' Open the specified file for read, write or both.''</font>
 Private Extern sf_open(path As String, mode As Integer, sfinfo As SF_INFO) As Pointer
 
 <FONT Color=gray>' ''sf_count_t int sf_format_check (const SF_INFO *info)''
 ' ''Return TRUE if fields of the SF_INFO struct are a valid combination of values.''</font>
 Private Extern sf_format_check(info As SF_INFO) As Integer
 
 <FONT Color=gray>' ''sf_count_t sf_read_float (SNDFILE *sndfile, float *ptr, sf_count_t items)''
 ' ''Function for reading the data chunk in terms of items.''</font>
 Private Extern sf_read_float(sndfile As Pointer, ptr As Pointer, items As Long) As Long
 
 <FONT Color=gray>' ''sf_count_t sf_write_float (SNDFILE *sndfile, float *ptr, sf_count_t items)''
 ' ''Function for writing the data chunk in terms of items.''</font>
 Private Extern sf_write_float(sndfile As Pointer, ptr As Pointer, items As Long) As Long
 
 <FONT Color=gray>' ''int sf_close (SNDFILE *sndfile)''
 ' ''Close the SNDFILE and clean up all memory allocations associated with this file.''</font>
 Private Extern sf_close(sndfile As Pointer) As Integer
 
 
 Public Sub Main()
 
  Dim buffer As New Single[4096]
  Dim infile, outfile As Pointer
  Dim sfinfo As New SF_INFO
  Dim fileorigine As String
 
  fileorigine = "<FONT Color=darkgreen>''/percorso/del/file/dati/audio/grezzi''</font>"
 
  infile = sf_open(fileorigine, SFM_READ, sfinfo)
  If infile == 0 Then Error.Raise("Impossibile aprire il file audio in entrata !")
 
 <FONT Color=gray>' ''Imposta le caratteristiche del file WAV:''</font>"
  With sfinfo
    .samplerate = 44100
    .channels = 2
    .format_ = SF_FORMAT_WAV Or SF_FORMAT_PCM_16
  End With
 
  If sf_format_check(sfinfo) == SF_FALSE Then 
    sf_close(infile)
    Error.Raise("Errore: codifica non valida !")
  Endif
 
  outfile = sf_open("<FONT Color=darkgreen>/tmp/file.wav</font>", SFM_WRITE, sfinfo)
  If outfile == 0 Then Error.Raise("Impossibile aprire il file audio in uscita !")
 
  Write "\e[5mAttendere...\e[0m"
  Flush
 
  While sf_read_float(infile, buffer.Data, buffer.Count) > 0
 <FONT Color=gray>' ''Scrive i dati audio nel file WAV:''</font>
    sf_write_float(outfile, buffer.Data, buffer.Count)
  Wend
 
  Write "\rConversione terminata !"
 
  sf_close(infile)
  sf_close(outfile)
 
 End