Eseguire un file Midi mediante le funzioni esterne del API di VLC

La libreria LibVLC consente di eseguire anche file MIDI, purché si abbiano installati nel sistema anche:

• vlc-plugin-fluidsynth - le risorse dei plugin di FluidSynth per VLC;
• fluid-soundfont-gm - Fluid (R3) General MIDI SoundFont (GM);
• ovviamente lo stesso FluidSynth.

E' possibile eseguire dati Midi anche direttamente da internet.

Per creare in Gambas un'applicazione con la presente risorsa, si dovranno installare e richiamare le librerie condivise "libvlc.so.5.6.1 " e "libSDL2-2.0.so.0.3000.7 ".

Esempio con applicazione grafica

Mostriamo di seguito un semplice esempio, nel quale si potrà avviare, arrestare, porre in pausa e riprendere l'esecuzione del file Midi:

Private inst As Pointer
Private mp As Pointer
Private m As Pointer


Library "libvlc:5.6.1"

Private Enum libvlc_NothingSpecial = 0,
        libvlc_Opening,
        libvlc_Buffering,
        libvlc_Playing,
        libvlc_Paused,
        libvlc_Stopped,
        libvlc_Ended,
        libvlc_Error

' 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_path (libvlc_instance_t *p_instance, const char *path)
' Create a media for a certain file path.
Private Extern libvlc_media_new_path(p_instance As Pointer, path As String) As Pointer

' libvlc_media_player_t * libvlc_media_player_new_from_media (libvlc_media_t *p_md)
' Create a Media Player object from a Media.
Private Extern libvlc_media_player_new_from_media(p_md As Pointer) As Pointer

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

' void libvlc_media_player_stop (libvlc_media_player_t * p_mi)
' Stop the audio file.
Private Extern libvlc_media_player_stop(p_mi As Pointer)

' libvlc_time_t libvlc_media_player_get_length(libvlc_media_player_t *, libvlc_exception_t *)
' Get the current movie length (in ms).
Private Extern libvlc_media_player_get_length(p_mi As Pointer, l_ex As Pointer) As Integer

' libvlc_time_t libvlc_media_player_get_time(libvlc_media_player_t * p_mi)
' Get the current movie time (in ms).
Private Extern libvlc_media_player_get_time(p_mi As Pointer) As Integer

' libvlc_state_t libvlc_media_player_get_state(libvlc_media_player_t *p_mi)
' Get current movie state.
Private Extern libvlc_media_player_get_state(p_mi As Pointer) As Integer

' void   libvlc_media_player_pause (libvlc_media_player_t *p_mi)
' Toggle pause.
Private Extern libvlc_media_player_pause(p_mi As Pointer)

' int libvlc_audio_set_volume(libvlc_media_player_t *p_mi, int i_volume)
' Set current software audio volume.
Private Extern libvlc_audio_set_volume(p_mi As Pointer, i_volume As Integer) 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)


Library "libSDL2-2.0:0.3000.7"

Private Const SDL_INIT_AUDIO As Integer = 16

' int SDL_Init(Uint32 flags)
' Initialize the SDL library.
Private Extern SDL_Init(flags As Integer) As Integer

' void SDL_Quit(void)
' Clean up all initialized subsystems.
Private Extern SDL_Quit()


Public Sub Form_Open()

 With Slider1
   .MaxValue = 100
   .MinValue = 0
   .Value = 50
 End With

End


Public Sub Button1_Click()
 
 SDL_Init(SDL_INIT_AUDIO)
   
' Inizializza la libreria VLC:
 inst = libvlc_new(0, Null)
   
' Crea un nuovo oggetto multimedia:
 m = libvlc_media_new_path(inst, "/percorso/del/file.mid")
   
' Crea un media play30er:
 mp = libvlc_media_player_new_from_media(m)

' Imposta il valore iniziale del volume dell'audio in base al valore iniziale dello "Slider":
 libvlc_audio_set_volume(mp, Slider1.Value)

' Avvia l'esecuzione del file Midi da parte del media player:
 libvlc_media_player_play(mp)

 Repeat 
   Wait 0.01
 Until libvlc_media_player_get_length(mp, 0) > 0.0

 Repeat
   TextLabel1.Text = "Durata: " & Str(Time(0, 0, 0, libvlc_media_player_get_length(mp, 0)))
   TextLabel2.Text = "<FONT Color=red>" & Str(Time(0, 0, 0, libvlc_media_player_get_time(mp)))
   ProgressBar1.Value = libvlc_media_player_get_time(mp) / libvlc_media_player_get_length(mp, 0)
   Wait 0.01
 Until libvlc_media_player_get_state(mp) > libvlc_Paused

 Chiude()

End


Public Sub Button2_Click()

' Arresta l'esecuzione del file Midi:
 libvlc_media_player_stop(mp)

End


Private Procedure Chiude()

' Chiude le librerie VLC e SDL:
 libvlc_media_player_release(mp)
 libvlc_media_release(m)
 libvlc_release(inst)
 SDL_Quit()
 
End


Public Sub ToggleButton1_Click()

' Pone in pausa o riprende (se già in pausa) l'esecuzione del file Midi:
 libvlc_media_player_pause(mp)

End


Public Sub Slider1_Change()

' Modifica il volume audio:
 If mp > 0 Then libvlc_audio_set_volume(mp, Slider1.Value)

End

Spostare l'esecuzione del file Midi nell'ambito della sua durata

Si può avanzare o retrocedere all'interno dell'esecuzione di un file Midi mediante la funzione esterna "libvlc_media_player_set_time()".

Innanzitutto si dichiarerà formalmente la funzione esterna "libvlc_media_player_set_time()" di libvlc:

' void libvlc_media_player_set_time (libvlc_media_player_t *p_mi, libvlc_time_t i_time)
' Set the movie time (in ms).
Private Extern libvlc_media_player_set_time(player As Pointer, i_time As Long)

Volendo usare uno Slider, imposteremo i valori iniziali dello Slider, dedicato allo spostamento dell'esecuzione del file Midi, nella routine:

Public Sub Form_Open()

 ......

 With Slider2
   .MaxValue = 1000
   .MinValue = 0
   .Value = 0
 End With

End

Inoltre imposteremo una specifica routine per lo Slider dedicato allo spostamento dell'esecuzione del file Midi:

Public Sub Slider2_Change()

' Sposta l'esecuzione del file Midi nell'ambito della sua durata:
 libvlc_media_player_set_time(mp, (Slider2.Value * libvlc_media_player_get_length(mp, 0)) / 1000)

End

Far variare la posizione del cursore dello Slider in base all'esecuzione

Se si preferisce far variare la posizione del cursore dello Slider in base al punto, all'evolversi dell'esecuzione del file Midi, e poter arbitrariamente far avanzare e retrocedere il punto dell'esecuzione muovendo il cursore dello Slider, allora potrà adottarsi un codice come il seguente:

Private inst As Pointer
Private mp As Pointer
Private m As Pointer
Private bo As Boolean


Library "libvlc:5.6.1"

Private Enum libvlc_NothingSpecial = 0, libvlc_Opening, libvlc_Buffering, libvlc_Playing,
             libvlc_Paused, libvlc_Stopped, libvlc_Ended, libvlc_Error

' 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_path (libvlc_instance_t *p_instance, const char *path)
' Create a media for a certain file path.
Private Extern libvlc_media_new_path(p_instance As Pointer, path As String) As Pointer

' libvlc_media_player_t * libvlc_media_player_new_from_media (libvlc_media_t *p_md)
' Create a Media Player object from a Media.
Private Extern libvlc_media_player_new_from_media(p_md As Pointer) 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_stop (libvlc_media_player_t * p_mi)
' Stop the video file.
Private Extern libvlc_media_player_stop(p_mi As Pointer)

' libvlc_time_t libvlc_media_player_get_length(libvlc_media_player_t *, libvlc_exception_t *)
' Get the current movie length (in ms).
Private Extern libvlc_media_player_get_length(p_mi As Pointer, l_ex As Pointer) As Integer

' libvlc_time_t libvlc_media_player_get_time(libvlc_media_player_t * p_mi)
' Get the current movie time (in ms).
Private Extern libvlc_media_player_get_time(p_mi As Pointer) As Integer

' libvlc_state_t libvlc_media_player_get_state(libvlc_media_player_t *p_mi)
' Get current movie state.
Private Extern libvlc_media_player_get_state(p_mi As Pointer) As Integer

' void libvlc_media_player_pause (libvlc_media_player_t *p_mi)
' Toggle pause.
Private Extern libvlc_media_player_pause(p_mi As Pointer)

' void libvlc_media_player_set_time (libvlc_media_player_t *p_mi, libvlc_time_t i_time)
' Set the movie time (in ms).
Private Extern libvlc_media_player_set_time(player As Pointer, i_time As Long)

' 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)

' void 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 Form_Open()

 With Slider1
   .MaxValue = 100
   .MinValue = 0
   .Value = 0
 End With

End


Public Sub Button1_Click()

 Slider1.Value = 0

 inst = libvlc_new(0, Null)

 m = libvlc_media_new_path(inst, "/percorso/del/file.mid")

 mp = libvlc_media_player_new_from_media(m)

 libvlc_media_player_play(mp)

 Repeat
   Wait 0.01
 Until libvlc_media_player_get_length(mp, 0) > 0.0

 Repeat
   Me.Title = "Durata: " & Str(Time(0, 0, 0, libvlc_media_player_get_length(mp, 0))) &
              " - " & Str(Time(0, 0, 0, libvlc_media_player_get_time(mp)))
   ProgressBar1.Value = libvlc_media_player_get_time(mp) / libvlc_media_player_get_length(mp, 0)
   If Not bo Then Slider1.Value = ProgressBar1.Value * 100
   Wait 0.01
 Until libvlc_media_player_get_state(mp) > libvlc_Paused

 Chiude()

End


Public Sub Button2_Click()

 libvlc_media_player_stop(mp)

 DrawingArea1.Clear

End


Private Procedure Chiude()

 libvlc_media_player_release(mp)
 libvlc_media_release(m)
 libvlc_release(inst)

End


Public Sub ToggleButton1_Click()

 libvlc_media_player_pause(mp)

End


Public Sub Slider1_MouseDown()

 bo = True

End


Public Sub Slider1_MouseUp()

 bo = False

 libvlc_media_player_set_time(mp, (Slider1.Value * libvlc_media_player_get_length(mp, 0)) / 100)

End

Esempio con effetto video

In quest'altro esempio mostreremo un effetto video (Spectrum analyzer) di VLC, che rappresenta un "Analizzatore di spettro", all'interno di una DrawingArea

Private inst As Pointer
Private mp As Pointer
 

Library "libvlc:5.6.1"

Private Enum libvlc_NothingSpecial = 0,
        libvlc_Opening,
        libvlc_Buffering,
        libvlc_Playing,
        libvlc_Paused,
        libvlc_Stopped,
        libvlc_Ended,
        libvlc_Error

' 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_path (libvlc_instance_t *p_instance, const char *path)
' Create a media for a certain file path.
Private Extern libvlc_media_new_path(p_instance As Pointer, path As String) As Pointer

' libvlc_media_player_t * libvlc_media_player_new_from_media (libvlc_media_t *p_md)
' Create a Media Player object from a Media.
Private Extern libvlc_media_player_new_from_media(p_md As Pointer) As Pointer

' void libvlc_media_player_set_xwindow (libvlc_media_player_t *p_mi, uint32_t drawable)
' Set an X Window System drawable where the media player should render its video output.
Private Extern libvlc_media_player_set_xwindow(p_mi As Pointer, drawable As Integer)

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

' void libvlc_media_player_stop (libvlc_media_player_t * p_mi)
' Stop the audio file.
Private Extern libvlc_media_player_stop(p_mi As Pointer)

' libvlc_time_t libvlc_media_player_get_length(libvlc_media_player_t *, libvlc_exception_t *)
' Get the current movie length (in ms).
Private Extern libvlc_media_player_get_length(p_mi As Pointer, l_ex As Pointer) As Integer

' libvlc_time_t libvlc_media_player_get_time(libvlc_media_player_t * p_mi)
' Get the current movie time (in ms).
Private Extern libvlc_media_player_get_time(p_mi As Pointer) As Integer

' libvlc_state_t libvlc_media_player_get_state(libvlc_media_player_t *p_mi)
' Get current movie state.
Private Extern libvlc_media_player_get_state(p_mi As Pointer) As Integer

' void   libvlc_media_player_pause (libvlc_media_player_t *p_mi)
' Toggle pause.
Private Extern libvlc_media_player_pause(p_mi As Pointer)

' 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_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)


Library "libSDL2-2.0:0.3000.7"

Private Const SDL_INIT_AUDIO As Integer = 16

' int SDL_Init(Uint32 flags)
' Initialize the SDL library.
Private Extern SDL_Init(flags As Integer) As Integer

' void SDL_Quit(void)
' Clean up all initialized subsystems.
Private Extern SDL_Quit()


Public Sub Button1_Click()

 Dim ss As String[]
 Dim m As Pointer
 Dim id As Integer
 
 SDL_Init(SDL_INIT_AUDIO)
  
 ss = ["--audio-visual=visual", "--effect-list=spectrum"]
  
' Inizializza la libreria VLC:
 inst = libvlc_new(ss.Count, ss)
   
' Crea un nuovo oggetto multimedia:
 m = libvlc_media_new_path(inst, "/percorso/del/file.mid")
   
' Crea un media player:
 mp = libvlc_media_player_new_from_media(m)
  
' Per far mostrare l'effetto video "Analizzatore di spettro" nella "DrawingArea", ricaviamo il suo identificativo:
 id = DrawingArea1.Id
  
' Passiamo l'identificativo della finestra, nella quale dovrà essere mostrato l'effetto "Spectrum analyzer":
 libvlc_media_player_set_xwindow(mp, id)
   
 ' Avvia l'esecuzione del file Midi da parte del media player:
 libvlc_media_player_play(mp)
 
 Repeat
   TextLabel1.Text = "Durata: " & Str(Time(0, 0, 0, libvlc_media_player_get_length(mp, 0)))
   TextLabel2.Text = "<FONT Color=red>" & Str(Time(0, 0, 0, libvlc_media_player_get_time(mp)))
   Wait 0.01
 Until libvlc_media_player_get_state(mp) > libvlc_Paused
 
 Chiude()

End


Public Sub Button2_Click()

' Arresta l'esecuzione del file Midi:
 libvlc_media_player_stop(mp)

End


Private Procedure Chiude()
   
' Chiude le librerie VLC e SDL:
 libvlc_media_player_release(mp)
 libvlc_media_release(m)
 libvlc_release(inst)
 SDL_Quit()
   
End


Public Sub ToggleButton1_Click()

' Pone in pausa o riprende (se già in pausa) l'esecuzione del file Midi:
 libvlc_media_player_pause(mp)

End

Esempio con applicazione a riga di comando

Library "libvlc:5.6.1"

Enum libvlc_NothingSpecial = 0,
     libvlc_Opening,
     libvlc_Buffering,
     libvlc_Playing,
     libvlc_Paused,
     libvlc_Stopped,
     libvlc_Ended,
     libvlc_Error

' 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_path (libvlc_instance_t *p_instance, const char *path)
' Create a media for a certain Midi file path.
Private Extern libvlc_media_new_path(p_instance As Pointer, path As String) As Pointer

' libvlc_media_player_t * libvlc_media_player_new_from_media (libvlc_media_t *p_md)
' Create a Media Player object from a Media.
Private Extern libvlc_media_player_new_from_media(p_md As Pointer) As Pointer

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

' libvlc_time_t libvlc_media_get_duration(libvlc_media_t *p_md)
' Get duration (in ms) of media descriptor object item.
Private Extern libvlc_media_get_duration(p_md As Pointer) As Long

' libvlc_time_t libvlc_media_player_get_time(libvlc_media_player_t * p_mi)
' Get the current movie time (in ms).
Private Extern libvlc_media_player_get_time(p_mi As Pointer) As Integer

' libvlc_state_t libvlc_media_player_get_state(libvlc_media_player_t *p_mi)
' Get current movie state.
Private Extern libvlc_media_player_get_state(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)


Library "libSDL2-2.0:0.3000.7"

Private Const SDL_INIT_AUDIO As Integer = 16

' int SDL_Init(Uint32 flags)
' Initialize the SDL library.
Private Extern SDL_Init(flags As Integer) As Integer

' void SDL_Quit(void)
' Clean up all initialized subsystems.
Private Extern SDL_Quit()


Public Sub Main()

 Dim m, inst, mp As Pointer
 Dim l As Long
 
 SDL_Init(SDL_INIT_AUDIO)
      
' Inizializza la libreria VLC:
 inst = libvlc_new(0, Null)
   
' Crea un nuovo oggetto multimedia:
 m = libvlc_media_new_path(inst, "/percorso/del/file.mid")
   
' Crea un media player:
 mp = libvlc_media_player_new_from_media(m)
   
 ' Avvia l'esecuzione del file Midi da parte del media player:
 libvlc_media_player_play(mp)
 
 Repeat 
   l = libvlc_media_get_duration(m)
 Until l > 0
 Print "Durata: "; Time(0, 0, 0, l)
 
 While libvlc_media_player_get_state(mp) <> libvlc_Ended
   Write "\r   \e[31m" & Str(Time(0, 0, 0, libvlc_media_player_get_time(mp)))
   Wait 0.01
 Wend
  
' Chiude la libreria VLC e il programma:
 libvlc_media_player_release(mp)
 libvlc_media_release(m)
 libvlc_release(inst)
 SDL_Quit()
  
End

Se si vuole consentire l'arresto arbitrario dell'esecuzione del file Midi, allora si dovrà rendere "Globale" la variabile Puntatore, chiamata "mp", e la parte finale del codice dovrà essere così modificata e integrata:

 ......

 While (libvlc_media_player_get_state(mp) <> libvlc_Stopped) And (libvlc_media_player_get_state(mp) <> libvlc_Ended)
   Write "\r   \e[31m" & Str(Time(0, 0, 0, libvlc_media_player_get_time(mp)))
   Wait 0.01
 Wend

' Chiude il media player, la libreria VLC e il programma:
 libvlc_media_player_release(mp)
 libvlc_release(inst)
 SDL_Quit()
' Avendo usato l'Evento "Application_Read()", è necessario usare l'istruzione "Quit" per chiudere il programma:
 Quit 

End

Public Sub Application_Read()

' Arresta l'esecuzione del file Midi:
 libvlc_media_player_stop(mp)

End

Esecuzione on-line di un file Midi da una pagina web

Per eseguire on-line un file Midi dal collegamento presente in una pagina web, bisognerà:
1) assicurarsi che l'indirizzo web, ove è ospitato il file Midi da eseguire, inizi con l'acronimo del protocollo "http" e non con "https";
2) utilizzare la funzione "libvlc_media_new_location( )" al posto della funzione "libvlc_media_new_path( )".

Esempio:

media = libvlc_media_new_location(instance, "http://www.indirizzo/web/del/file.mid")

Riferimenti

• http://www.videolan.org/developers/vlc/doc/doxygen/html/index.html
• https://wiki.videolan.org/Midi Videolan