Versione delle 08:38, 22 lug 2020

E' possibile ottenere un file audio formato WAV da un file Midi mediante una linea di pipeline gestita dalla funzione gst parse launch() del API di GStreamer.

Mostriamo un esempio pratico:

Library "libgstreamer-1.0"

Private Enum GST_STATE_VOID_PENDING = 0, GST_STATE_NULL, GST_STATE_READY, GST_STATE_PAUSED, GST_STATE_PLAYING
Private Const GST_FORMAT_TIME As Integer = 3
Private stato As Integer = GST_STATE_PLAYING

' gst_init (int *argc, char **argv[])
' Initializes the GStreamer library, setting up internal path lists, registering built-in elements, and loading standard plugins.
Private Extern gst_init(argc As Pointer, argv As Pointer)

' GstElement * gst_parse_launch (const gchar *pipeline_description, GError **error)
' Create a new pipeline based on command line syntax.
Private Extern gst_parse_launch(description As String, GError As Pointer) As Pointer

' GstStateChangeReturn gst_element_set_state(GstElement *element, GstState state)
' Sets the state of the element.
Private Extern gst_element_set_state(gstelement As Pointer, state As Integer) As Integer

' gboolean gst_element_query_duration(GstElement *element, GstFormat format, gint64 *duration)
' Queries an element for the total stream duration in nanoseconds.
Private Extern gst_element_query_duration(gselement As Pointer, formatI As Integer, duration As Pointer) As Boolean

' void gst_object_unref(gpointer object)
' Decrements the reference count on object.
Private Extern gst_object_unref(gobject As Pointer)


Public Sub Main()
 
 Dim midi As Pointer
 Dim volume As Float
 Dim durata As Long
 Dim dur, tempus As Date
 Dim dd As Integer
     
 gst_init(0, 0)
  
 midi = gst_parse_launch("filesrc location=/percorso/del/file.mid ! decodebin ! audioconvert ! audioresample ! volume volume=7.0 ! wavenc ! filesink location =/tmp/file.wav", 0)
       
' Avviamo la riproduzione del file Midi per la creazione del file audio WAV:
 gst_element_set_state(midi, GST_STATE_PLAYING)
 
 Repeat
   gst_element_query_duration(midi, GST_FORMAT_TIME, VarPtr(durata))
   dur = Date(0, 0, 0, 0, 0, 0, durata / 1000000)
 Until dur > 0
 
 tempus = Now
 
 Repeat
   dd = DateDiff(tempus, Now, gb.Millisecond)
   Write "\r\e[0mDurata: " & dur & "      Pos. \e[31m" & CStr(Date(0, 0, 0, 0, 0, 0, dd))
   Wait 0.001
 Until dd > (durata / 1000000)
  
 gst_object_unref(midi)
 Print "\nCreazione del file audio WAV terminata."
      
End

Riferimenti

• http://docs.gstreamer.com/display/GstSDK/gst-launch
• http://gstreamer.freedesktop.org/
• http://gstreamer.com/