Modificare la frequenza di campionamento di un file audio con l'API di Libresample e Libsndfile
Da Gambas-it.org - Wikipedia.
Versione del 4 mar 2016 alle 10:01 di Vuott (Discussione | contributi)
La libreria Libresample, creata da Dominic Mazzoni, consente di modificare la frequenza di campionamento (Sample Rate) di un file audio.
Per poter fruire in Gambas delle risorse della libreria Libresample, bisognera installare e richiamare la libreria dinamica condivisa: "libresample.so.1.0"
Nell'esempio che segue si farà uso anche della libreria SndFile.
Library "libresample:1.0"
' void *resample_open(int highQuality, double minFactor, double maxFactor)
Private Extern resample_open(highQuality As Integer, minFactor As Float, maxFactor As Float) As Pointer
' int resample_process(void *handle, double factor, float *inBuffer, int inBufferLen, int lastFlag, int *inBufferUsed, float *outBuffer, int outBufferLen)
Private Extern resample_process(handleP As Pointer, factor As Float, inBUffer As Single[], inBufferLen As Integer, lastFlag As Integer, inBufferUsed As Pointer, outBuffer As Single[], outBufferLen As Integer) As Integer
Library "libsndfile:1.0.25"
Public Struct SF_INFO
frames As Long
samplerate As Integer
channels As Integer
formatI As Integer
sections As Integer
seekable As Integer
End Struct
Public Struct SF_FORMAT_INFO
formatI As Integer
name As Pointer
extension As Pointer
End Struct
Private Const SFM_READ As Integer = &10
Private Const SFM_WRITE As Integer = &20
Private Enum SFC_GET_FORMAT_MAJOR_COUNT = &1030, SFC_GET_FORMAT_MAJOR
Private Const SF_FORMAT_SUBMASK As Integer = &0000FFFF
' 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, SFinf As SF_INFO) As Pointer
' int sf_command (SNDFILE *sndfile, int command, void *data, int datasize)
' Return TRUE if fields of the SF_INFO struct are a valid combination of values.
Private Extern sf_command(snd As Pointer, command As Integer, data As Pointer, datasize As Integer)
' sf_count_t sf_readf_float (SNDFILE *sndfile, float *ptr, sf_count_t frames)
' Reads the data chunk in terms of frames. Passes data in the native float format.
Private Extern sf_readf_float(snd As Pointer, ptr As Single[], frames As Long) As Long
' sf_count_t sf_writef_float (SNDFILE *sndfile, const float *ptr, sf_count_t frames)
' Writes the data chunk in terms of frames. Passes data in the native float format.
Private Extern sf_writef_float(snd As Pointer, ptr As Single[], 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(snd As Pointer) As Integer
Public Sub Main()
Dim srcinfo, dstinfo As New SF_INFO
Dim formatinfo As New SF_FORMAT_INFO
Dim srcfile, dstfile, p As Pointer
Dim dsti, src, dst, srci As Single[]
Dim handle As Pointer[]
Dim dstrate, srcrate, ratio As Float
Dim channels, numformats, i, c, srclen, dstlen As Integer
Dim pos, bufferpos, outcount, block, lastFlag As Integer
Dim inUsed, inused2, out, out2 As Integer
Dim extension As String
Dim FileAudioIn As String = "/percorso/del/file/audio/originario"
Dim FileAudioOut As String = "/percorso/del/file/audio/finale/modificato"
' Imposta la nuova frequenza di campionamento del file audio:
dstrate = 22050.00
If (dstrate < 10.0) Or (dstrate > 100000.0) Then Error.Raise("Valore della frequenza di campionamento non consentita !")
srcfile = sf_open(FileAudioIn, SFM_READ, srcinfo)
If IsNull(srcfile) Then Error.Raise("Impossibile aprire il file audio in entrata !")
Print "File audio in entrata: "; FileAudioIn
Print "Frequenza campionamento: "; srcinfo.samplerate; " Hertz"
Print "Canali n. "; srcinfo.channels
srcrate = srcinfo.samplerate
If dstrate = 0.0 Then
dstrate = srcrate * ratio
Else
ratio = dstrate / srcrate
Endif
channels = srcinfo.channels
' Estrae il formato del file di destinazione:
extension = File.Ext(FileAudioOut)
If "." & extension Then
sf_command(Null, SFC_GET_FORMAT_MAJOR_COUNT, VarPtr(numformats), SizeOf(gb.Integer))
Print "\nLa libreria 'libresample' supporta "; numformats; " formati audio: "
p = Alloc(Object.SizeOf(formatinfo))
For i = 0 To numformats - 1
formatinfo.formatI = i
sf_command(Null, SFC_GET_FORMAT_MAJOR, p, Object.SizeOf(formatinfo))
formatinfo = p
Print String@(formatinfo.extension); " ";
If Not Comp(String@(formatinfo.extension), extension) Then
Print "\nSi sta usando "; String@(formatinfo.name); " come formato in uscita."
dstinfo.formatI = formatinfo.formatI Or (srcinfo.formatI And SF_FORMAT_SUBMASK)
Break
Endif
Next
Free(p)
Endif
If Not dstinfo.formatI Then
If (extension) Then Error.Raise("Attenzione: il formato in uscita " & extension & " non è riconosciuto. Usare lo stesso formato del file originario !")
dstinfo.formatI = srcinfo.formatI
Endif
dstinfo.samplerate = CInt(dstrate + 0.5)
dstinfo.channels = channels
dstfile = sf_open(FileAudioOut, SFM_WRITE, dstinfo)
If IsNull(dstfile) Then Error.Raise("Impossibile aprire il file audio in uscita !")
Print "\n\nFile sorgente: "; FileAudioIn; " ("; srcinfo.frames; " frames, ", srcrate; " Hz)"
Print "File destinazione: "; FileAudioOut; " ("; dstrate; " Hz, ratio = "; ratio
srclen = 4096
dstlen = (srclen * ratio + 1000)
srci = New Single[](srclen * channels * SizeOf(gb.Single))
dsti = New Single[](dstlen * channels * SizeOf(gb.Single))
src = New Single[](srclen * SizeOf(gb.Single))
dst = New Single[](dstlen * SizeOf(gb.Single))
handle = New Pointer[](channels * SizeOf(gb.Pointer))
For c = 0 To channels - 1
handle[c] = resample_open(1, ratio, ratio)
Next
While pos < srcinfo.frames
block = Min(srclen - bufferpos, srcinfo.frames - pos)
lastFlag = (pos + block == srcinfo.frames)
sf_readf_float(srcfile, srci, block)
block += bufferpos
For c = 0 To channels - 1
For i = 0 To block - 1
src[i] = srci[i * channels + c]
Next
inUsed = 0
out = resample_process(handle[c], ratio, src, block, lastFlag, VarPtr(inUsed), dst, dstlen)
If c = 0
inUsed2 = inUsed
out2 = out
Else
If (inUsed2 <> inUsed) Or (out2 <> out) Then Error.Raise("Grave errore: canali fuori sincronizzazione !")
Endif
For i = 0 To out - 1
If dst[i] <= -1 Then
dsti[i * channels + c] = -1
Else If dst[i] >= 1
dsti[i * channels + c] = 1
Else
dsti[i * channels + c] = dst[i]
Endif
Next
Next
sf_writef_float(dstfile, dsti, out)
bufferpos = block - inUsed
For i = 0 To i < (bufferpos * channels) - 1
srci[i] = srci[i + (inUsed * channels)]
pos += inUsed
outcount += out
Next
Wend
' Va in chiusura:
sf_close(srcfile)
sf_close(dstfile)
End
