Convertire un file WAV in formato OggVorbis con le funzioni esterne del API di libsndfile

La conversione dei formati audio mediante le sole risorse di Sndfile è abbastanza semplice.

E' necessario avere installata nel proprio sistema e richiamare in Gambas la libreria condivisa: "libsndfile.so.1.0.31 ".

Mostriamo un semplice esempio, nel quale si convertirà un file WAV in un file OGG-Vorbis:

Private Const LUN_BUFF As Long = 4096

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_VORBIS As Integer = &60
Private Const SF_FORMAT_OGG As Integer = &200000

' SNDFILE * sf_open (const char *path, int mode, SF_INFO *sfinfo)
' Open the specified file for read, write or both.
Private Extern sf_open(path As String, mode As Integer, sfinfo As SF_INFO) As Pointer

' 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.
Private Extern sf_format_check(info As SF_INFO) As Integer

' sf_count_t sf_readf_short (SNDFILE *sndfile, short *ptr, sf_count_t frames)
' Function for reading the data chunk in terms of frames.
Private Extern sf_readf_short(sndfile As Pointer, ptr As Pointer, frames As Long) As Long

' sf_count_t sf_writef_short (SNDFILE *sndfile, const short *ptr, sf_count_t frames)
' Function for writing the data chunk in terms of frames.
Private Extern sf_writef_short(sndfile As Pointer, ptr As Pointer, frames As Long) As Long

' int sf_close (SNDFILE *sndfile)
' Close the SNDFILE and clean up all memory allocations associated with this file.
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 = "/percorso/del/file.wav"

 infile = sf_open(fileorigine, SFM_READ, sfinfo)
 If infile == 0 Then Error.Raise("Impossibile aprire il file audio in entrata !")

' Imposta le caratteristiche del file OGG:"
 With sfinfo
   .samplerate = 44100
   .channels = 2
   .format_ = SF_FORMAT_VORBIS Or SF_FORMAT_OGG
 End With

 If sf_format_check(sfinfo) == SF_FALSE Then 
   sf_close(infile)
   Error.Raise("Errore: codifica non valida !")
 Endif

 outfile = sf_open("/tmp/file.wav", 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, buffer.Count) > 0
' Scrive i dati audio nel file OGG-Vorbis:
   sf_write_float(outfile, buffer, buffer.Count)
 Wend

 Write "\rConversione terminata !"

 sf_close(infile)
 sf_close(outfile)

End