Impostare il volume dei singoli due canali del mixer di ALSA
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Versione del 26 apr 2016 alle 04:48 di Vuott (Discussione | contributi) (Creata pagina con "Utilizzando alcune risorse dell'interfaccia ''Mixer'' di ALSA, è possibile - fra l'altro - impostare e modificare il volume audio di ciascuno dei due canali del mixer. Sarà...")
Utilizzando alcune risorse dell'interfaccia Mixer di ALSA, è possibile - fra l'altro - impostare e modificare il volume audio di ciascuno dei due canali del mixer.
Sarà ovviamente necessario richiamare in Gambas la libreria dinamica condivisa di ALSA: "libasound.so.2.0.0"
Mostriamo un semplice esempio, nel quale bisognerà scrivere nell'apposito spazio al di sotto della console (oppure nel Terminale) del progetto Gambas un valore compreso tra 0 e 100 per impostare il volume audio di ciascun canale del mixer di ALSA per volta.
Library "libasound:2.0.0"
Private Enum SND_MIXER_SCHN_MONO = 0, SND_MIXER_SCHN_FRONT_LEFT = 0, SND_MIXER_SCHN_FRONT_RIGHT
' int snd_mixer_open (snd_mixer_t **mixer, int mode)
' Opens an empty mixer.
Private Extern snd_mixer_open(mixer As Pointer, mode As Integer) As Integer
' int snd_mixer_attach (snd_mixer_t *mixer, const char *name)
' Attach an HCTL specified with the CTL device name to an opened mixer.
Private Extern snd_mixer_attach(mixer As Pointer, name As String) As Integer
' int snd_mixer_selem_register (snd_mixer_t *mixer, struct snd_mixer_selem_regopt *options, snd_mixer_class_t **classp)
' Register mixer simple element class.
Private Extern snd_mixer_selem_register(mixer As Pointer, options As Pointer, classp As Pointer) As Integer
' int snd_mixer_load (snd_mixer_t *mixer)
' Load a mixer elements.
Private Extern snd_mixer_load(mixer As Pointer) As Integer
' int snd_mixer_selem_id_malloc (snd_mixer_selem_id_t **ptr)
' Allocate an invalid snd_mixer_selem_id_t using standard malloc.
Private Extern snd_mixer_selem_id_malloc(ptr As Pointer) As Integer
' void snd_mixer_selem_id_set_index (snd_mixer_selem_id_t *obj, unsigned int val)
' Set index part of a mixer simple element identifier.
Private Extern snd_mixer_selem_id_set_index(obj As Pointer, ival As Integer)
' void snd_mixer_selem_id_set_name (snd_mixer_selem_id_t *obj, const char *val)
' Set name part of a mixer simple element identifier.
Private Extern snd_mixer_selem_id_set_name(obj As Pointer, sval As String)
' snd_mixer_elem_t * snd_mixer_find_selem (snd_mixer_t *mixer, const snd_mixer_selem_id_t *id)
' Find a mixer simple element.
Private Extern snd_mixer_find_selem(mixer As Pointer, id As Pointer) As Pointer
' int snd_mixer_selem_set_playback_volume (snd_mixer_elem_t *elem, snd_mixer_selem_channel_id_t channel, long value)
' Set value of playback volume control of a mixer simple element.
Private Extern snd_mixer_selem_set_playback_volume(elem As Pointer, channel As Integer, value As Integer) As Integer
' int snd_mixer_close (snd_mixer_t *mixer)
' Close a mixer and free all related resources.
Private Extern snd_mixer_close(mixer As Pointer) As Integer
Public Sub Main()
Dim handle, sid, el As Pointer
Dim err, i As Integer
Dim can, vol As String
Dim volume As Long
err = snd_mixer_open(VarPtr(handle), 0)
If err < 0 Then Error.Raise("Impossibile inizializzare il sub-sistema 'Mixer' di ALSA !")
snd_mixer_attach(handle, "default")
snd_mixer_selem_register(handle, 0, 0)
snd_mixer_load(handle)
snd_mixer_selem_id_malloc(VarPtr(sid))
snd_mixer_selem_id_set_index(sid, 0)
snd_mixer_selem_id_set_name(sid, "Master")
el = snd_mixer_find_selem(handle, sid)
can = "sinistro."
For i = 0 to SND_MIXER_SCHN_FRONT_RIGHT
if i = SND_MIXER_SCHN_FRONT_RIGHT Then can = "destro."
Print "Immettere un valore (0 - 100) per impostare il volume del canale "; can
Input vol
volume = CLong(Val(vol))
snd_mixer_selem_set_playback_volume(el, i, volume * 65536 / 100)
Next
' Va in chiusura:
snd_mixer_close(handle)
End
