Registrare in tempo reale in un file l'audio di una radio WEB con le funzioni esterne del API di VLC

Con le riorse di VLC è possibile ascoltare e contemporaneamente registrare in un file audio in tempo reale i dati audio trasmessi da una radio WEB.

Mostriamo il seguente esempio partico in ambiente grafico:

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 ToggleButton1_Click()

 Dim inst, mp, m As Pointer
 Dim tm As Date

 If ToggleButton1.Value Then

' Inizializza la libreria VLC:
   inst = libvlc_new(0, Null)

' Crea un nuovo oggetto multimedia.
' Nel secondo argomento della funzione va specificato l'indirizzo del flusso di dati audio trasmessi dalla radio web:
   m = libvlc_media_new_location(inst, "https://stream.rockantenne.de/70er-rock/stream/mp3?aw_0_1st.playerid=radio.de")

' Imposta i parametri per il formato audio e per creare il file audio:
   libvlc_media_add_option(m, ":sout=#transcode{acodec=mp3,ab=128,samplerate=44100,channels=2}:duplicate{dst=display,dst=std{access=file,mux=mp3,dst=/tmp/audio.mp3}}") ' ...o anche "mux=raw".

' 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
     Me.Title = 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)
   Me.Close
 Else
' Causa l'arresto della registrazione, la chiusura della libreria VLC e del programma:
   bo = True
 Endif

End