Versione delle 16:47, 12 giu 2021

La funzione esterna gst_parse_launch() della libreria GStreamer consente di costruire e gestire in modo semplice una pipeline GStreamer. La riga della pipeline gestita dalla funzione esterna gst_parse_launch() è un insieme di elementi separati da punti esclamativi (!). Le proprietà possono essere aggiunte agli elementi, sotto forma di: proprietà = valore.

Sarà necessario avere installata nel sistema e richiamare nell'applicazione Gambas la libreria dinamica condivisa: "libgstreamer-1.0"

Usando i plugin "wavescope" o "monoscope" unitamente a "autoaudiosink" all'interno della riga della pipeline della funzione gst_parse_launch(), è possibile scegliere la visualizzazione di due tipi diversi di oscilloscopio attivo durante l'esecuzione di un file Midi.

Uso del plugin wavescope

Mostriamo un esempio pratico usando i plugin "wavescope" e "autoaudiosink" all'interno della riga della pipeline della funzione gst_parse_launch():

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
 
' 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 ! midiparse ! fluiddec ! tee name=t " &
                         "! queue ! audioconvert ! wavescope style=3 ! video/x-raw, width=1000 ! videoconvert ! ximagesink t. " &
                         "! queue ! audioconvert ! m. t. ! queue ! volume volume=7.0 ! autoaudiosink", 0)
             
' Avviamo l'esecuzione del file midi:
 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(Time(0, 0, 0, dd))
   Wait 0.001
 Until dd > (durata / 1000000)
  
 gst_object_unref(midi)
 Print "\nEsecuzione terminata."
 
End

Uso del plugin monoscope

Mostriamo un esempio pratico usando i plugin "monoscope" e "autoaudiosink" all'interno della riga della pipeline della funzione gst_parse_launch():

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
 
' 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 ! midiparse ! fluiddec ! " &
                         "tee name=t ! queue ! audioconvert ! monoscope ! ximagesink ! queue ! m. t. ! " &
                         "queue ! volume volume=7.0 ! autoaudiosink", 0)
                
' Avviamo l'esecuzione del file Midi:
 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(Time(0, 0, 0, dd))
   Wait 0.001
 Until dd > (durata / 1000000)
 
 gst_object_unref(midi)
 Print "\nEsecuzione terminata."
  
End

Riferimenti

• http://docs.gstreamer.com/display/GstSDK/gst-launch
• https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-bad-plugins/html/gst-plugins-bad-plugins-wavescope.html
• https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-good-plugins/html/gst-plugins-good-plugins-monoscope.html
• http://gstreamer.freedesktop.org/
• http://gstreamer.com/