Differenze tra le versioni di "Eseguire un file WAV usando l'API di SndFile e di Alsa"
Da Gambas-it.org - Wikipedia.
Riga 35: | Riga 35: | ||
Private Const SND_PCM_ACCESS_RW_INTERLEAVED As Byte = 3 | Private Const SND_PCM_ACCESS_RW_INTERLEAVED As Byte = 3 | ||
Private Const SND_PCM_FORMAT_U8 As Byte = 1 | Private Const SND_PCM_FORMAT_U8 As Byte = 1 | ||
− | |||
− | + | <FONT color=gray>' ''int snd_pcm_open(snd_pcm_t **pcm, const char *name, snd_pcm_stream_t stream, int mode)'' | |
− | <FONT color=gray>' ''int | + | ' ''Opens a PCM.''</font> |
Private Extern snd_pcm_open(pcmP As Pointer, nome As String, stream As Integer, mode As Integer) As Integer | Private Extern snd_pcm_open(pcmP As Pointer, nome As String, stream As Integer, mode As Integer) As Integer | ||
− | <FONT color=gray>' ''const char * snd_strerror (int errnum) | + | <FONT color=gray>' ''const char * snd_strerror (int errnum)'' |
+ | ' ''Returns the message For an Error code.''</font> | ||
Private Extern snd_strerror(errnum As Integer) As String | Private Extern snd_strerror(errnum As Integer) As String | ||
− | <FONT color=gray>' ''int snd_pcm_set_params (snd_pcm_t *pcm, snd_pcm_format_t format, snd_pcm_access_t access, unsigned int channels, unsigned int rate, int soft_resample, unsigned int latency) | + | <FONT color=gray>' ''int snd_pcm_set_params (snd_pcm_t *pcm, snd_pcm_format_t format, snd_pcm_access_t access, unsigned int channels, unsigned int rate, int soft_resample, unsigned int latency)'' |
' ''Set the hardware And software parameters In aPrivate Const MPG123_ADD_FLAGS As Byte = 2 simple way.''</font> | ' ''Set the hardware And software parameters In aPrivate Const MPG123_ADD_FLAGS As Byte = 2 simple way.''</font> | ||
Private Extern snd_pcm_set_params(pcmP As Pointer, formatB As Byte, accessB As Byte, channels As Integer, rate As Integer, soft_resample As Integer, latency As Integer) As Integer | Private Extern snd_pcm_set_params(pcmP As Pointer, formatB As Byte, accessB As Byte, channels As Integer, rate As Integer, soft_resample As Integer, latency As Integer) As Integer | ||
− | <FONT color=gray>' ''snd_pcm_sframes_t snd_pcm_writei(snd_pcm_t *pcm, const void *buffer, snd_pcm_uframes_t size)''</font> | + | <FONT color=gray>' ''snd_pcm_sframes_t snd_pcm_writei(snd_pcm_t *pcm, const void *buffer, snd_pcm_uframes_t size)'' |
+ | ' ''Write interleaved frames to a PCM.''</font> | ||
Private Extern snd_pcm_writei(pcmP As Pointer, buffP As Pointer, uframes As Long) As Integer | Private Extern snd_pcm_writei(pcmP As Pointer, buffP As Pointer, uframes As Long) As Integer | ||
− | <FONT color=gray>' ''int snd_pcm_close(snd_pcm_t **pcm)''</font> | + | <FONT color=gray>' ''int snd_pcm_drain (snd_pcm_t *pcm)'' |
+ | ' ''Stop a PCM preserving pending frames.''</font> | ||
+ | Private Extern snd_pcm_drain(pcmP As Pointer) As Integer | ||
+ | |||
+ | <FONT color=gray>' ''int snd_pcm_close(snd_pcm_t **pcm)'' | ||
+ | ' ''Close PCM handle.''</font> | ||
Private Extern snd_pcm_close(pcmP As Pointer) | Private Extern snd_pcm_close(pcmP As Pointer) | ||
− | '''Public''' Sub | + | '''Public''' Sub Main() |
Dim infile, buffer, handle As Pointer | Dim infile, buffer, handle As Pointer | ||
Dim sfinfo As New SF_INFO | Dim sfinfo As New SF_INFO | ||
− | Dim err, frequenza, conto, frames, canali As Integer | + | Dim err, frequenza, conto, frames, canali, somma As Integer |
Riga 65: | Riga 71: | ||
<FONT color=gray>' ''Apre il file wav:''</font> | <FONT color=gray>' ''Apre il file wav:''</font> | ||
− | infile = sf_open("/percorso/del/file.wav", SFM_READ, sfinfo) | + | infile = sf_open("<FONT color=gray>''/percorso/del/file.wav''</font>", SFM_READ, sfinfo) |
<FONT color=gray>' ''Ricava la frequenza di campionamento ed il numero di canali del file wav:''</font> | <FONT color=gray>' ''Ricava la frequenza di campionamento ed il numero di canali del file wav:''</font> | ||
Riga 76: | Riga 82: | ||
' ''Qui inizia la parte relativa alle funzioni di Alsa:''</font> | ' ''Qui inizia la parte relativa alle funzioni di Alsa:''</font> | ||
− | err = snd_pcm_open(VarPtr(handle), | + | err = snd_pcm_open(VarPtr(handle), "default", SND_PCM_STREAM_PLAYBACK, 0) |
If err < 0 Then Error.Raise("Playback open error: " & snd_strerror(err)) | If err < 0 Then Error.Raise("Playback open error: " & snd_strerror(err)) | ||
Riga 93: | Riga 99: | ||
' ''al valore del 3° argomento della precedente funzione "sf_read_short" diviso il numero di canali del file audio:''</font> | ' ''al valore del 3° argomento della precedente funzione "sf_read_short" diviso il numero di canali del file audio:''</font> | ||
frames = snd_pcm_writei(handle, <FONT color=darkorange><B>buffer</b></font>, BUFFER_LEN / sfinfo.channels) | frames = snd_pcm_writei(handle, <FONT color=darkorange><B>buffer</b></font>, BUFFER_LEN / sfinfo.channels) | ||
− | + | If (frames < 0) Then Error.Raise("Errore alla funzione 'snd_pcm_writei': " & snd_strerror(err)) | |
− | + | ||
− | + | somma += conto | |
− | + | Write "\r" & CStr(Date(0, 0, 0, 0, 0, 0, (somma / frequenza) * 1000)) | |
− | + | ||
Loop While conto <> 0 | Loop While conto <> 0 | ||
+ | |||
+ | <FONT color=gray>' ''Impedisce che al termine l'esecuzione venga troncata inaspettatamente:''</font> | ||
+ | snd_pcm_drain(handle) | ||
<FONT color=gray>' ''Va in chiusura:''</font> | <FONT color=gray>' ''Va in chiusura:''</font> | ||
snd_pcm_close(handle) | snd_pcm_close(handle) | ||
sf_close(infile) | sf_close(infile) | ||
+ | Free(buffer) | ||
'''End''' | '''End''' |
Versione delle 03:37, 27 ott 2015
SndFile è una libreria, scritta in C, per leggere e scrivere file che contengono suono campionato (come il formato WAV ed il formato AIFF) attraverso una libreria interfaccia standard.
Pertanto, coniugheremo le librerie di SndFile e di Alsa, assegnando a SndFile il compito di leggere ed estrarre i dati del file audio, ed ad Alsa quello di eseguire tali dati audio.
Mostreremo di seguito un semplice codice per l'esecuzione di un file wav:
Public Struct SF_INFO frames As Long samplerate As Integer channels As Integer formatI As Integer sections As Integer seekable As Integer End Struct Library "libsndfile:1.0.25" ' SNDFILE * sf_open (const char *path, int mode, SF_INFO *sfinfo) --> Apre un file per la lettura Private Extern sf_open(path As String, mode As Integer, SFinf As SF_INFO) As Pointer ' sf_count_t sf_read_short(SNDFILE *sndfile, float *ptr, sf_count_t items) --> Legge i dati del file wav Private Extern sf_read_short(sndfile As Pointer, ptr As Pointer, items As Integer) As Integer ' int sf_close (SNDFILE *sndfile) --> Chiude il file precedentemente aperto Private Extern sf_close(sndfile As Pointer) As Integer Private Const BUFFER_LEN As Short = 1024 Private Const SFM_READ As Byte = 16 Library "libasound:2" Private Const SND_PCM_STREAM_PLAYBACK As Byte = 0 Private Const SND_PCM_ACCESS_RW_INTERLEAVED As Byte = 3 Private Const SND_PCM_FORMAT_U8 As Byte = 1 ' int snd_pcm_open(snd_pcm_t **pcm, const char *name, snd_pcm_stream_t stream, int mode) ' Opens a PCM. Private Extern snd_pcm_open(pcmP As Pointer, nome As String, stream As Integer, mode As Integer) As Integer ' const char * snd_strerror (int errnum) ' Returns the message For an Error code. Private Extern snd_strerror(errnum As Integer) As String ' int snd_pcm_set_params (snd_pcm_t *pcm, snd_pcm_format_t format, snd_pcm_access_t access, unsigned int channels, unsigned int rate, int soft_resample, unsigned int latency) ' Set the hardware And software parameters In aPrivate Const MPG123_ADD_FLAGS As Byte = 2 simple way. Private Extern snd_pcm_set_params(pcmP As Pointer, formatB As Byte, accessB As Byte, channels As Integer, rate As Integer, soft_resample As Integer, latency As Integer) As Integer ' snd_pcm_sframes_t snd_pcm_writei(snd_pcm_t *pcm, const void *buffer, snd_pcm_uframes_t size) ' Write interleaved frames to a PCM. Private Extern snd_pcm_writei(pcmP As Pointer, buffP As Pointer, uframes As Long) As Integer ' int snd_pcm_drain (snd_pcm_t *pcm) ' Stop a PCM preserving pending frames. Private Extern snd_pcm_drain(pcmP As Pointer) As Integer ' int snd_pcm_close(snd_pcm_t **pcm) ' Close PCM handle. Private Extern snd_pcm_close(pcmP As Pointer) Public Sub Main() Dim infile, buffer, handle As Pointer Dim sfinfo As New SF_INFO Dim err, frequenza, conto, frames, canali, somma As Integer buffer = Alloc(BUFFER_LEN * 4) ' Apre il file wav: infile = sf_open("/percorso/del/file.wav", SFM_READ, sfinfo) ' Ricava la frequenza di campionamento ed il numero di canali del file wav: With sfinfo frequenza = .samplerate canali = .channels End With '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ' Qui inizia la parte relativa alle funzioni di Alsa: err = snd_pcm_open(VarPtr(handle), "default", SND_PCM_STREAM_PLAYBACK, 0) If err < 0 Then Error.Raise("Playback open error: " & snd_strerror(err)) err = snd_pcm_set_params(handle, 2, SND_PCM_ACCESS_RW_INTERLEAVED, canali, frequenza, 1, 500000) If err < 0 Then Error.Raise("Playback open error: " & snd_strerror(err)) ' Inizia il ciclo per la scrittura dei dati e per l'esecuzione del file wav: Do ' Legge i dati del file wav e li carica nel buffer: conto = sf_read_short(infile, buffer, BUFFER_LEN) ' I dati audio vengono inviati al sub-sistema "PCM" di Alsa, attraverso la lettura della variabile ' qui denominata "buffer". La quantità unitaria di dati scritti nell'handle del sub-sistema PCM deve essere uguale ' al valore del 3° argomento della precedente funzione "sf_read_short" diviso il numero di canali del file audio: frames = snd_pcm_writei(handle, buffer, BUFFER_LEN / sfinfo.channels) If (frames < 0) Then Error.Raise("Errore alla funzione 'snd_pcm_writei': " & snd_strerror(err)) somma += conto Write "\r" & CStr(Date(0, 0, 0, 0, 0, 0, (somma / frequenza) * 1000)) Loop While conto <> 0 ' Impedisce che al termine l'esecuzione venga troncata inaspettatamente: snd_pcm_drain(handle) ' Va in chiusura: snd_pcm_close(handle) sf_close(infile) Free(buffer) End
Riferimenti
- Il sito del API di SndFile.