Ridurre a 8-bit la risoluzione di campionamento di un file audio WAV con le funzioni esterne del API di Sox
Da Gambas-it.org - Wikipedia.
La libreria Sox contiene risorse per poter gestire ampiamente i file audio: riproduzione e registrazione, conversione di vari formati audio in altri formati, nonché applicazione di vari effetti. Sox consente di eseguire numerosissimi formati di file audio.
Per poter diminuire a 8-bit la risoluzione di campionamento di un file WAV, campionato ad esempio a 16-bit, bisognerà impostare con il valore della Costante SOX_ENCODING_UNSIGNED il membro "->encoding.encoding" della Struttura sox_format_t, relativa ai nuovi dati del nuovo file wav.
E' necessario avere installata nel proprio sistema e richiamare in Gambas la libreria condivisa: "libsox.so.3.0.0 ".
Mostriamo un esempio, nel quale un file di formato WAV a 16-bit, 44100 hertz, viene diminuita a 8-bit la risoluzione di campionamento e a 8000 hertz la frequenza di campionamento:
Library "libsox:3.0.0
Public Struct sox_signalinfo_t
rate As Float
channels As Integer
precision As Integer
length As Long
mult As Pointer
End Struct
Public Struct sox_encodinginfo_t
encoding As Integer
bits_per_sample As Integer
compression As Float
reverse_bytes As Integer
reverse_nibbles As Integer
reverse_bits As Integer
opposite_endian As Integer
End Struct
Public Struct sox_effects_globals_t
plot As Integer
global_info As Pointer
End Struct
Public Struct sox_effects_chain_t
effects As Pointer
table_size As Integer
length As Integer
ibufc As Pointer
obufc As Pointer
global_info As Struct Sox_effects_globals_t
in_enc As Pointer
out_enc As Pointer
End Struct
Public Struct sox_effect_handler_t
name As Pointer
usage As Pointer
flags As Integer
sox_effect_handler_getopts As Pointer
sox_effect_handler_start As Pointer
sox_effect_handler_flow As Pointer
sox_effect_handler_drain As Pointer
sox_effect_handler_stop As Pointer
sox_effect_handler_kill As Pointer
priv_size As Long
End Struct
Public Struct sox_effect_t
global_info As Pointer
in_signal As Struct Sox_signalinfo_t
out_signal As Struct Sox_signalinfo_t
in_encoding As Pointer
out_encoding As Pointer
handler As Struct Sox_effect_handler_t
obuf As Pointer
obeg As Long
oend As Long
imin As Long
clips As Long
flows As Long
flow As Long
priv As Pointer
End Struct
Private Enum SOX_EOF = -1, SOX_SUCCESS, SOX_EHDR = 2000, SOX_EFMT, SOX_ENOMEM, SOX_EPERM, SOX_ENOTSUP, SOX_EINVAL
Private Const SOX_ENCODING_UNSIGNED As Integer = 2
Private Const SOX_UNSPEC As Integer = 0
Private Const SOX_EFF_LENGTH As Integer = 8
' int sox_format_init(void)
' Client API: Initialize effects library. SOX_SUCCESS if successful.
Private Extern sox_init() As Integer
' sox_format_t * sox_open_read(char const *path, sox_signalinfo_t const *signal, sox_encodinginfo_t const *encoding, char const *filetype)
' Opens a decoding session for a file. returns the handle for the new session, or null on failure.
Private Extern sox_open_read(path As String, signal As Sox_signalinfo_t, encoding As sox_encodinginfo_t, filetype As String) As Pointer
' sox_format_t * sox_open_write(char const *path, sox_signalinfo_t const *signal, sox_encodinginfo_t const *encoding, char const *filetype, sox_oob_t const *oob, sox_bool(*overwrite_permitted)(const char *filename)
' Opens a decoding session for a file. returns the handle for the new session, or null on failure.
Private Extern sox_open_write(path As String, signal As Sox_signalinfo_t, encoding As Sox_encodinginfo_t, filetype As String, oob As Pointer, filename As String) As Pointer
' sox_effects_chain_t * sox_create_effects_chain(sox_encodinginfo_t const * in_enc, sox_encodinginfo_t const * out_enc)
' Initializes an effects chain.
Private Extern sox_create_effects_chain(in_enc As Sox_encodinginfo_t, out_enc As Sox_encodinginfo_t) As Sox_effects_chain_t
' sox_effect_t * sox_create_effect(sox_effect_handler_t const * eh)
' Creates an effect using the given handler.
Private Extern sox_create_effect(eh As Sox_effect_handler_t) As Sox_effect_t
' sox_effect_handler_t const * sox_find_effect(char const * name)
' Finds the effect handler with the given name.
Private Extern sox_find_effect(name As String) As Pointer
' int sox_effect_options(sox_effect_t *effp, int argc, char * const argv[])
' Applies the command-line options to the effect.
Private Extern sox_effect_options(effp As Sox_effect_t, argc As Integer, argv As Pointer[]) As Integer
' int sox_add_effect(sox_effects_chain_t * chain, sox_effect_t * effp, sox_signalinfo_t * in, sox_signalinfo_t const * out)
' Adds an effect to the effects chain, returns SOX_SUCCESS if successful. Returns SOX_SUCCESS if successful.
Private Extern sox_add_effect(chain As Sox_effects_chain_t, effp As Sox_effect_t, inS As Sox_signalinfo_t, ouS As Sox_signalinfo_t) As Integer
' int sox_flow_effects(sox_effects_chain_t * chain, sox_flow_effects_callback callback, void * client_data)
' Runs the effects chain, returns SOX_SUCCESS if successful. Returns SOX_SUCCESS if successful.
Private Extern sox_flow_effects(chain As Sox_effects_chain_t, callback As Pointer, client_data As Pointer) As Integer
' void sox_delete_effects_chain(sox_effects_chain_t *ecp)
' Closes an effects chain.
Private Extern sox_delete_effects_chain(chain As Sox_effects_chain_t)
' int sox_close(sox_format_t * ft)
' Closes an encoding or decoding session.
Private Extern sox_close(ft As Pointer) As Integer
' int sox_quit(void)
' Close effects library and unload format handler plugins. Returns SOX_SUCCESS if successful.
Private Extern sox_quit()
Public Sub Main()
Dim fileAUDIO As String
Dim err As Integer
Dim sfIn, sfOut As Pointer
Dim sigIn, sigOut As New Sox_signalinfo_t
Dim encoIn, encoOut As New Sox_encodinginfo_t
Dim chain As Sox_effects_chain_t
Dim eff As New Sox_effect_t
Dim argsP As New Pointer[10]
Dim st As Stream
Dim s As Short
fileAUDIO = "/percorso/del/file/audio.wav"
' Inizializza la libreria "libsox":
err = sox_init()
If err <> SOX_SUCCESS Then Error.Raise("Impossibile inizializzare la libreria 'libsox' !")
sfIn = sox_open_read(fileAUDIO, Null, Null, Null)
If sfIn == 0 Then Error.Raise("Impossibile aprire il file audio !")
sigIn = sfIn + SizeOf(gb.Pointer)
With sigIn
Print "File audio \e[31msorgente\e[0m: ", String@(Pointer@(sfIn))
Print "Frequenza di campionamento: ", .rate; " hertz"
Print "Canali: ", .channels
Print "Risoluzione: ", .precision; " bit"
Print "Quantità dati audio: ", .length * .channels; " byte"
Print "Durata: ", Str(Time(0, 0, 0, (((.length * .channels) * 8) / (.rate * .channels * .precision)) * 1000))
End With
' Sostituisce la necessaria funzione "memcpy()" di C, con le seguenti 5 righe:
sfOut = Alloc(SizeOf(gb.Byte), 728)
st = Memory sfOut For Write
For s = 0 To 727
Write #st, Byte@(sfIn + CInt(s)) As Byte
Next
st.Close
encoOut = sfOut + (SizeOf(gb.Pointer) * 5)
With encoOut
.encoding = SOX_ENCODING_UNSIGNED
.bits_per_sample = 8
End With
sigOut = sfOut + SizeOf(gb.Pointer)
With sigOut
.rate = 8000
.precision = 16
.length = SOX_UNSPEC
End With
Free(sfOut)
' Imposta il "percorso" del nuovo file da creare:
sfOut = sox_open_write("/percorso/del/nuovo/file/audio.wav", sigOut, encoOut, Null, 0, Null)
If sfOut == 0 Then Error.Raise("Impossibile aprire il nuovo file audio per la scrittura !")
encoIn = sfIn + (SizeOf(gb.Pointer) * 5)
chain = sox_create_effects_chain(encoIn, encoOut)
eff = sox_create_effect(sox_find_effect("input"))
argsP[0] = sfIn
err = sox_effect_options(eff, 1, argsP)
If err <> SOX_SUCCESS Then Error.Raise("Errore nella funzione 'sox_effect_options' !")
err = sox_add_effect(chain, eff, sigIn, sigIn)
If err <> SOX_SUCCESS Then Error.Raise("Errore nella funzione 'sox_add_effect' !")
If sigIn.rate <> sigOut.rate Then
eff = sox_create_effect(sox_find_effect("rate"))
err = sox_effect_options(eff, 0, Null)
If err <> SOX_SUCCESS Then Error.Raise("Errore nella funzione 'sox_effect_options' !")
eff.handler.flags = eff.handler.flags Or SOX_EFF_LENGTH
err = sox_add_effect(chain, eff, sigIn, sigOut)
If err <> SOX_SUCCESS Then Error.Raise("Errore nella funzione 'sox_add_effect' !")
Endif
If sigIn.channels <> sigOut.channels Then
eff = sox_create_effect(sox_find_effect("channels"))
sox_effect_options(eff, 0, Null)
sox_add_effect(chain, eff, sigIn, sigOut)
Endif
eff = sox_create_effect(sox_find_effect("output"))
argsP[0] = sfOut
sox_effect_options(eff, 1, argsP)
sox_add_effect(chain, eff, sigIn, sigOut)
' Esegue i dati audio:
sox_flow_effects(chain, Null, Null)
' Va in chiusura:
Free(argsP.Data)
sox_delete_effects_chain(chain)
sox_close(sfOut)
sox_close(sfIn)
sox_quit()
End
