Convertire i file audio da un formato ad un altro con le funzioni esterne del API di VLC

La libreria libvlc consente di convertire tra loro i seguenti formati audio: FLV, MP3, OGG e WAV.

E' necessario avere installata nel proprio sistema la libreria condivisa: "libvlc.so.5.6.1 ".

Mostriamo un esempio pratico a riga di comando:

Private bo As Boolean


Library "libvlc:5.6.1"

' libvlc_instance_t * libvlc_new (int argc, const char *const *argv)
' Create And initialize a libvlc instance.
Private Extern libvlc_new(argc As Integer, argv As String[]) As Pointer

' libvlc_media_t *libvlc_media_new_location(libvlc_instance_t *p_instance, const char * psz_mrl)
' Create a media with a certain given media resource location, for instance a valid URL.
Private Extern libvlc_media_new_location(p_instance As Pointer, path As String) As Pointer

' void libvlc_media_add_option (libvlc_media_t *p_md, const char *psz_options)
' Add an option to the media.
Private Extern libvlc_media_add_option(p_mi As Pointer, psz_options As String)

' libvlc_media_player_t * libvlc_media_player_new(libvlc_instance_t *p_libvlc_instance)
' Create an empty Media Player object.
Private Extern libvlc_media_player_new(p_libvlc_instance As Pointer) As Pointer

' void libvlc_media_player_set_media(libvlc_media_player_t *p_mi, libvlc_media_t *p_md)
' Set the media that will be used by the media_player.
Private Extern libvlc_media_player_set_media(p_md As Pointer, mp As Pointer)

' int libvlc_media_player_play (libvlc_media_player_t * p_mi)
' Play the video file.
Private Extern libvlc_media_player_play(p_mi As Pointer) As Integer

' void libvlc_media_player_release (libvlc_media_player_t * p_mi)
' Release a media_player after use Decrement the reference count of a media player object.
Private Extern libvlc_media_player_release(p_mi As Pointer)

' void libvlc_media_release (libvlc_media_t *p_md)
' Decrement the reference count of a media descriptor object.
Private Extern libvlc_media_release(p_md As Pointer)

' libvlc_release (libvlc_instance_t * p_instance)
' Decrement the reference count of a libvlc instance, and destroy it if it reaches zero.
Private Extern libvlc_release(p_instance As Pointer)


Public Sub Main()
 
 Dim inst, mp, m As Pointer
 Dim tm As Date
 
' Inizializza la libreria VLC:
 inst = libvlc_new(0, Null)

' Carica il file audio da convertire
 m = libvlc_media_new_path(inst, "/percorso/del/file/audio")

' Imposta i parametri per il formato audio e per creare il nuovo file audio, in questo caso di formato OGG-Vorbis:
 libvlc_media_add_option(m, ":sout=#transcode{acodec=vorb,ab=96,channels=2}:standard{access=file,mux=ogg,dst=/tmp/audio.ogg}")

' Crea il media player:
 mp = libvlc_media_player_new(inst)

 libvlc_media_player_set_media(mp, m)

 libvlc_media_release(m)

' Avvia la registrazione audio da parte del media player:
 libvlc_media_player_play(mp)

 tm = Now

 While bo = False
   Write "\r" & = Str(Time(0, 0, 0, DateDiff(tm, Now, gb.Millisecond))
' Il Wait consente di agire su altri oggetti posti sul Form:
   Wait 0.01
 Wend

' Chiude la libreria VLC ed il programma:
 libvlc_media_player_release(mp)
 libvlc_release(inst)
 Print "\nConversione audio terminata !"
  
End

Convertire in altri formati audio

Convertire in formato MP3

Impostare i parametri audio come appresso:

libvlc_media_add_option(m, ":sout=#transcode{acodec=mp3,ab=192,channels=2}:standard{access=file,mux=mp3,dst=/tmp/audio.mp3}")

Convertire in formato WAV

Impostare i parametri audio come appresso:

libvlc_media_add_option(m, ":sout=#transcode{acodec=s16l,ab=128,channels=2}:standard{access=file,mux=wav,dst=/tmp/audio.wav}")

Convertire in formato FLV

Impostare i parametri audio come appresso:

libvlc_media_add_option(m, ":sout=#transcode{acodec=mp3,ab=128,channels=2}:standard{access=file,mux=flv,dst=/tmp/audio.flv}")