Conoscere con le funzioni esterne di ALSA i dispositivi audio presenti nel sistema

Alcune funzioni esterne del API di ALSA consentono di conoscere quali sono i dispositivi audio delle schede audio presenti nel proprio sistema.

Mostriamo due esempi, nei quali sul Form dell'applicativo porremo una ListBox.

Di seguito il primo possibile codice:

Private Const SND_PCM_STREAM_PLAYBACK As Byte = 0   ' Playback stream
Private Const ENOENT As Byte = 2
 

Library "libasound:2"

' int snd_card_next(int *card)
' Try to determine the next card.
Private Extern snd_card_next(cardI As Pointer) As Integer

' const char* snd_pcm_stream_name(snd_pcm_stream_t stream)
' Get name of PCM stream type
Private Extern snd_pcm_stream_name(streamI As Byte) As String

' int snd_ctl_open(snd_ctl_t **ctl, const char *name, int mode)
' Opens a CTL.
Private Extern snd_ctl_open(ctlP As Pointer, name As String, mode As Integer) As Integer

' snd_ctl_card_info_malloc(ptr)
' Allocate an invalid snd_ctl_card_info_t using standard malloc
Private Extern snd_ctl_card_info_malloc(ptr As Pointer)

' int snd_ctl_card_info(snd_ctl_t *ctl, snd_ctl_card_info_t *info)
' Get card related information.
Private Extern snd_ctl_card_info(ctlP As Pointer, infoP As Pointer) As Integer

' void snd_ctl_close(snd_ctl_t *ctl)
' Closes a ctl.
Private Extern snd_ctl_close(ctlP As Pointer)

' int snd_ctl_pcm_next_device(snd_ctl_t *ctl, int *device)
' Get Next PCM device number.
Private Extern snd_ctl_pcm_next_device(ctlP As Pointer, device As Pointer) As Integer

' int snd_pcm_info_malloc(snd_pcm_info_t ** ptr)
' Allocate an invalid snd_pcm_info_t using standard malloc.
Private Extern snd_pcm_info_malloc(ptr As Pointer) As Integer

' void snd_pcm_info_set_device (snd_pcm_info_t *obj, unsigned int val)
' Set wanted device inside a PCM info container.
Private Extern snd_pcm_info_set_device(pcminfoP As Pointer, ValI As Integer)

' void snd_pcm_info_set_subdevice(snd_pcm_info_t *obj, unsigned int val)
' Set wanted subdevice inside a PCM info container.
Private Extern snd_pcm_info_set_subdevice(pcminfoP As Pointer, ValI As Integer)

' void snd_pcm_info_set_stream(snd_pcm_info_t *obj, snd_pcm_stream_t val)
' Set wanted stream inside a PCM info container.
Private Extern snd_pcm_info_set_stream(pcminfoP As Pointer, valInt As Integer)

' int snd_ctl_pcm_info (snd_ctl_t *ctl, snd_pcm_info_t *info)
' Get info about a PCM device.
Private Extern snd_ctl_pcm_info(ctlP As Pointer, pcminfoP As Pointer) As Integer

' const char * snd_ctl_card_info_get_id (const snd_ctl_card_info_t *obj)
' Get card identifier From a CTL card info.
Private Extern snd_ctl_card_info_get_id(infoP As Pointer) As String

' const char * snd_ctl_card_info_get_name (const snd_ctl_card_info_t *obj)
' Get card name From a CTL card info.
Private Extern snd_ctl_card_info_get_name(infoP As Pointer) As String

' const char* snd_pcm_info_get_id(const snd_pcm_info_t * obj)
' Get id from a PCM info container.
Private Extern snd_pcm_info_get_id(pcminfoP As Pointer) As String

' const char* snd_pcm_info_get_name (const snd_pcm_info_t * obj)
' Get name From a PCM info container.
Private Extern snd_pcm_info_get_name(pcminfoP As Pointer) As String

' unsigned int  snd_pcm_info_get_subdevices_count (const snd_pcm_info_t *obj)
' Get subdevices count From a PCM info container.
Private Extern snd_pcm_info_get_subdevices_count(pcminfoP As Pointer) As Integer

' unsigned int snd_pcm_info_get_subdevices_avail (const snd_pcm_info_t *obj)
' Get available subdevices count From a PCM info container.
Private Extern snd_pcm_info_get_subdevices_avail(pcminfoP As Pointer) As Integer

' const char * snd_pcm_info_get_subdevice_name (const snd_pcm_info_t *obj)
' Get subdevice name From a PCM info container.
Private Extern snd_pcm_info_get_subdevice_name(pcminfoP As Pointer) As String

' const char * snd_strerror (int errnum)
' Returns the message For an Error code.
Private Extern snd_strerror(errore As Integer) As String
 

Public Sub Form_Open()

 Me.show
 
 Do
   Wait 0.1
 Loop Until Me.Id <> 0

 Lista_Dispositivi()

End


Private Procedure Lista_Dispositivi()

 Dim handlCtl, info, pcminfo As Pointer
 Dim card, dev, count, avail, idx, err As Integer
 Dim name, card_id, card_name, pcm_id, pcm_name, subdevice_name As String

 
  snd_ctl_card_info_malloc(VarPtr(info))
  snd_pcm_info_malloc(VarPtr(pcminfo))
   
  card = -1

  If (snd_card_next(VarPtr(card)) < 0) Or (card < 0) Then
    Error("Nessuna scheda audio trovata !")
    Return
  Endif

  ListBox1.Add("******* LISTA DEI DISPOSITIVI HARDWARE DI RIPRODUZIONE AUDIO *******")
   
  snd_pcm_stream_name(SND_PCM_STREAM_PLAYBACK)

  While card >= 0

    name = "hw:" & card

    err = snd_ctl_open(VarPtr(handlCtl), name, 0)
    If err < 0 Then
      Error("Apertura del Controllo: " & card & ":" & snd_strerror(err))
      Goto next_card
    Endif
    
    err = snd_ctl_card_info(handlCtl, info)
    If err < 0 Then
      Error("Informazione sull'hardware del controllo: " & card & ":" & snd_strerror(err))
      snd_ctl_close(handlCtl)
      Goto next_card
    Endif
     
    dev = -1
     
    While True

      If snd_ctl_pcm_next_device(handlCtl, VarPtr(dev)) < 0 Then Error("Errore alla funzione 'snd_ctl_pcm_next_device' !")

      If dev < 0 Then Break
      
      snd_pcm_info_set_device(pcminfo, dev)
       
      snd_pcm_info_set_subdevice(pcminfo, 0)
       
      snd_pcm_info_set_stream(pcminfo, SND_PCM_STREAM_PLAYBACK)

      err = snd_ctl_pcm_info(handlCtl, pcminfo)

      If err < 0 Then
        If err <> - ENOENT Then Error.Raise("Informazione sull'audio digitale del controllo: " & card & " " & snd_strerror(err))
        Continue
      Endif
       
      card_id = snd_ctl_card_info_get_id(info)
       
      card_name = snd_ctl_card_info_get_name(info)
       
      pcm_id = snd_pcm_info_get_id(pcminfo)
       
      pcm_name = snd_pcm_info_get_name(pcminfo)
       
      With ListBox1
        .Add("_______________________________________________________________________________________")
        .Add(" ")
        .Add("DISPOSITIVO AUDIO: " & name & "  " & card_id & " [" & card_name & "]    Device: " & dev & "  " & pcm_id & " [" & pcm_name & "]")
        .Add(" ")
      End With

      count = snd_pcm_info_get_subdevices_count(pcminfo)
       
      avail = snd_pcm_info_get_subdevices_avail(pcminfo)
       
      With ListBox1
        .Add("Subdevices: " & avail & "/" & count)
        .Add(" ")
      End With
       
      For idx = 0 To count - 1
        snd_pcm_info_set_subdevice(pcminfo, idx)
        err = snd_ctl_pcm_info(handlCtl, pcminfo)
        If err < 0 Then
          Error("Informazione sulla Riproduzione audio digitale del controllo: " & card & " " & snd_strerror(err))
        Else
          subdevice_name = snd_pcm_info_get_subdevice_name(pcminfo)
          ListBox1.Add("Subdevice: #" & idx & ":  " & subdevice_name)
        Endif
      Next
        
    Wend

    snd_ctl_close(handlCtl)
    next_card:
    If snd_card_next(VarPtr(card)) < 0 Then
      Error("Errore in 'next_card' !")
      Break
    Endif
 
  Wend

End

Di seguito invece il secondo possibile codice:

Library "libasound:2"

Private Const SND_PCM_STREAM_PLAYBACK As Integer = 0
Private Const SND_PCM_STREAM_CAPTURE As Integer = 1

' int snd_card_next(int *card)
' Try to determine the next card.
Private Extern snd_card_next(cardI As Pointer) As Integer

' int snd_ctl_open (snd_ctl_t **ctl, const char *name, int mode)
' Opens a CTL.
Private Extern snd_ctl_open(card As Pointer, name As String, mode As Integer) As Integer

' int snd_ctl_pcm_next_device (snd_ctl_t *ctl, int *device)
' Get Next pcm device number.
Private Extern snd_ctl_pcm_next_device(ctl As Pointer, device As Pointer) As Integer

' int snd_ctl_card_info_malloc (snd_ctl_card_info_t **ptr)
' Allocate an invalid snd_ctl_card_info_t using standard malloc.
Private Extern snd_ctl_card_info_malloc(ptr As Pointer) As Integer

' int snd_ctl_card_info (snd_ctl_t *ctl, snd_ctl_card_info_t *info)
' Get card related information.
Private Extern snd_ctl_card_info(ctl As Pointer, snd_ctl_card_info_t As Pointer) As Integer

' const char * snd_ctl_card_info_get_longname (const snd_ctl_card_info_t *obj)
' Get card long name from a CTL card info.
Private Extern snd_ctl_card_info_get_longname(obj As Pointer) As String

' const char * snd_ctl_card_info_get_id (const snd_ctl_card_info_t *obj)
' Get card identifier from a CTL card info.
Private Extern snd_ctl_card_info_get_id(obj As Pointer) As String

' const char * snd_ctl_card_info_get_name (const snd_ctl_card_info_t *obj)
' Get card name from a CTL card info.
Private Extern snd_ctl_card_info_get_name(obj As Pointer) As String

' const char * snd_ctl_card_info_get_driver (const snd_ctl_card_info_t *obj)
' Get card driver name from a CTL card info.
Private Extern snd_ctl_card_info_get_driver(obj As Pointer) As String

' const char * snd_ctl_card_info_get_mixername (const snd_ctl_card_info_t *obj)
' Get card mixer name from a CTL card info.
Private Extern snd_ctl_card_info_get_mixername(obj As Pointer) As String

' const char * snd_ctl_card_info_get_components (const snd_ctl_card_info_t *obj)
' Get card component list from a CTL card info.
Private Extern snd_ctl_card_info_get_components(obj As Pointer) As String

' int snd_pcm_info_malloc (snd_pcm_info_t **ptr)
' Allocate a New Snd_pcm_info_t structure.
Private Extern snd_pcm_info_malloc(ptr As Pointer) As Integer

' size_t snd_pcm_info_sizeof (void)
' Get size Of the 'snd_pcm_info_t' structure in bytes.
Private Extern snd_pcm_info_sizeof() As Integer

' void snd_pcm_info_set_device (snd_pcm_info_t *obj, unsigned int val)
' Set pcm device number.
Private Extern snd_pcm_info_set_device(obj As Pointer, ValInt As Integer)

' void snd_pcm_info_set_stream (snd_pcm_info_t *obj, snd_pcm_stream_t val)
' Set pcm stream identifier.
Private Extern snd_pcm_info_set_stream(obj As Pointer, ValInt As Integer)

' void snd_pcm_info_set_subdevice (snd_pcm_info_t *obj, unsigned int val)
' Set pcm subdevice number.
Private Extern snd_pcm_info_set_subdevice(obj As Pointer, ValInt As Integer)

' int snd_ctl_pcm_info (snd_ctl_t *ctl, snd_pcm_info_t *info)
' Get info about a pcm device.
Private Extern snd_ctl_pcm_info(ctl As Pointer, info As Pointer) As Integer

' unsigned int snd_pcm_info_get_subdevices_count (const snd_pcm_info_t *obj)
' Get pcm count of subdevices.
Private Extern snd_pcm_info_get_subdevices_count(obj As Pointer) As Integer

' unsigned int snd_pcm_info_get_subdevices_avail (const snd_pcm_info_t *obj)
' Get pcm available count of subdevices.
Private Extern snd_pcm_info_get_subdevices_avail(obj As Pointer) As Integer

' const char * snd_pcm_info_get_id (const snd_pcm_info_t *obj)
' Get pcm hardware driver identifier.
Private Extern snd_pcm_info_get_id(obj As Pointer) As String

' const char * snd_pcm_info_get_name (const snd_pcm_info_t *obj)
' Get pcm hardware driver name.
Private Extern snd_pcm_info_get_name(obj As Pointer) As String

' const char * snd_pcm_info_get_subdevice_name (const snd_pcm_info_t *obj)
' Get pcm subdevice name.
Private Extern snd_pcm_info_get_subdevice_name(obj As Pointer) As String

' int snd_ctl_close (snd_ctl_t *ctl)
' Closes CTL handle.
Private Extern snd_ctl_close(ctl As Pointer) As Integer

' int snd_config_update_free_global (void)
' Frees the global configuration tree In snd_config.
Private Extern snd_config_update_free_global() As Integer

' const char * snd_strerror (int errnum)
' Returns the message For an Error code.
Private Extern snd_strerror(errore As Integer) As String

' void *memset(void *str, int c, size_t n)
' Copies the character c (an unsigned char) to the first n characters of the string pointed to by the argument str.
Private Extern memset(StrP As Pointer, c As Integer, n As Integer) As Pointer In "libc:6"


Public Sub Form_Open()

 Me.show

 Do
   Wait 0.1
 Loop Until Me.Id <> 0

 Lista_Dispositivi()

End


Public Sub Lista_Dispositivi()

 Dim err, cardNum, devNum, unaVolta As Integer
 Dim audioHandle, cardInfo As Pointer
 Dim $str As String


  ListBox1.Add("---- DISPOSITIVI HARDWARE AUDIO PRESENTI ----")

  cardNum = -1


  While True

    err = snd_card_next(VarPtr(cardNum))
    If err < 0 Then Error.Raise("Impossibile ottenere il numero della scheda audio successiva: " & snd_strerror(err))
 
' Se non vi sono più schede, Alsa imposta "cardNum" a -1:
    If cardNum < 0 Then Exit
   
    $str = "hw:" & CStr(cardNum)

    err = snd_ctl_open(VarPtr(audioHandle), $Str, 0)
    If err < 0 Then Error.Raise("Impossibile aprire la connessione con la scheda audio: " & snd_strerror(err))
     
    unaVolta = 0
     
' Parte con il primo dispositivo audio sulla scheda individuata:
    devNum = -1

    While True

' Ricava il numero del successivo dispositivo Midi sulla scheda attuale:
      err = snd_ctl_pcm_next_device(audioHandle, VarPtr(devNum))
      If err < 0 Then Error.Raise("Impossibile ottenere il numero del successivo dispositivo audio: " & snd_strerror(err))

' Se non ci sono altri dispositivi audio sulla scheda audio, Alsa imposta "devNum" a -1.
' NOTA: E' possibile che la scheda audio (ad esempio una scheda audio digitale) possa non avere dispositivi audio:
      If devNum < 0 Then Exit

      If Not unaVolta Then

' Esegue il codice qui sotto una sola volta:
        unaVolta = 1       
     
        snd_ctl_card_info_malloc(VarPtr(cardInfo))
    
' Dice ad ALSA di riempire 'snd_ctl_card_info_t' con informazioni sulla corrente scheda:
        err = snd_ctl_card_info(audioHandle, cardInfo)
        If err < 0 Then
          Error.Raise("Impossibile ottenere informazioni sulla scheda audio: " & snd_strerror(err))
        Else
          With ListBox1
            .Add(" ")
            .Add(" ")
            .Add("=================================================================================")
            .Add(snd_ctl_card_info_get_longname(cardInfo))
            .Add("=================================================================================")
            .Add("id = " & snd_ctl_card_info_get_id(cardInfo))
            .Add("nome = " & snd_ctl_card_info_get_name(cardInfo))
            .Add("driver = " & snd_ctl_card_info_get_driver(cardInfo))
            .Add("mixername = " & snd_ctl_card_info_get_mixername(cardInfo))
            .Add("componenti = " & snd_ctl_card_info_get_components(cardInfo))
          End With
        Endif
    
      Endif
    
' Mostra le informazioni relative ai subdispositivi audio Output del corrente dispositivo audio:
      lista_subdevice(audioHandle, cardNum, devNum, SND_PCM_STREAM_PLAYBACK)
  
' Mostra le informazioni relative ai subdispositivi audio Input del corrente dispositivo audio:
      lista_subdevice(audioHandle, cardNum, devNum, SND_PCM_STREAM_CAPTURE)

    Wend

    snd_ctl_close(audioHandle)
 
  Wend

' Va in chiusura liberando la memoria precedentemente allocata:
  snd_config_update_free_global()

End


Private Procedure lista_subdevice(audioH As Pointer, cardN As Integer, devN As Integer, tipo As Integer)
 
 Dim pcmInfo As Pointer
 Dim subDevCount, i, err As Integer
 Dim stringa As String


  If tipo = SND_PCM_STREAM_PLAYBACK Then
    stringa = "Output"
  Else
    stringa = "Input"
  Endif
  
  snd_pcm_info_malloc(VarPtr(pcmInfo))
  memset(pcmInfo, 0, snd_pcm_info_sizeof())

' Dice ad ALSA di quale dispositivo Audio si richiedono le informazioni:
  snd_pcm_info_set_device(pcmInfo, devN)
   
' Si ottengono informazioni sull'uscita Audio o in sezione del corrente dispositivo:
  snd_pcm_info_set_stream(pcmInfo, tipo)
    
  i = -1
  subDevCount = 1
  
  Inc i
  While i < subDevCount

' Dice ad ALSA di riempire 'snd_pcm_info_t' con le informazioni sul corrente subdispositivo:
    snd_pcm_info_set_subdevice(pcmInfo, i)

    err = snd_ctl_pcm_info(audioH, pcmInfo)
    If err < 0 Then
      ListBox1.Add("Impossibile ottenere informazioni sul subdevice " & stringa & " Audio 'hw:" & CStr(cardN) & "," & CStr(devN) & "," & CStr(i) & " : " & snd_strerror(err))
      Exit
    Endif
  
' Scrive quanti subdispositivi audio sono presenti:
    If Not i Then
      subDevCount = snd_pcm_info_get_subdevices_count(pcmInfo)
      With ListBox1
        .Add(" ")
        .Add("------ " & subDevCount & " " & stringa & " subdevice (" & snd_pcm_info_get_subdevices_avail(pcmInfo) & " disponibili)")
        .Add("id = " & snd_pcm_info_get_id(pcmInfo))
        .Add("nome = " & snd_pcm_info_get_name(pcmInfo))
      End With
    Endif
  
' NOTA: Se è presente un solo subdispositivo, allora il numero del subdispositivo è immateriale, e può essere omesso:
    If subDevCount > 1 Then
      ListBox1.Add(" ")
      ListBox1.Add("   AUDIO " & stringa & " 'hw:" & cardN & "," & devN & "," & i & "'")
    Else
      ListBox1.Add(" ")
      ListBox1.Add("   AUDIO " & stringa & " 'hw:" & cardN & "," & devN & "'")
    Endif

    ListBox1.Add("   subnome = '" & snd_pcm_info_get_subdevice_name(pcmInfo) & "'")
  
    Inc i

  Wend

End