Visualizzare un oscilloscopio di GStreamer mediante la funzione 'gst parse launch()' durante l'esecuzione di un file audio

Da Gambas-it.org - Wikipedia.

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 audio di formato wav, mp3 ed .ogg.


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(): 

Private audio As Pointer


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
 
' gboolean gst_element_query_position(GstElement * element, GstFormat format, gint64 * cur)
' Queries an element For the stream position In nanoseconds.
Private Extern gst_element_query_position(gstelement As Pointer, gstformat As Pointer, cur 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 pos, dur As Long
 Dim po, du As Date
     
  gst_init(0, 0)
  
  audio = gst_parse_launch("filesrc location=/percorso/del/file/audio ! decodebin ! tee name=t " &
                           "! queue ! audioconvert ! wavescope style=3 ! video/x-raw, width=1000 ! videoconvert ! ximagesink t. " &
                           "! queue ! audioconvert ! m. t. ! queue ! autoaudiosink", 0)
             
' Avviamo l'esecuzione del file audio:
  gst_element_set_state(audio, GST_STATE_PLAYING)
  
  While True
    gst_element_query_position(audio, GST_FORMAT_TIME, VarPtr(pos))
    gst_element_query_duration(audio, GST_FORMAT_TIME, VarPtr(dur))
    po = Date(0, 0, 0, 0, 0, 0, pos / 1000000)
    du = Date(0, 0, 0, 0, 0, 0, dur / 1000000)
    If (pos > 0) And (CStr(po) >= CStr(du)) Then Break
    Write #File.Out, "\rDurata: " & du & "      " & "Tempo trascorso: " & po
  Wend
  
  Termina()
        
End


Public Sub Application_Read()
  
 Dim s As String
 
  Input #File.In, s
  
  Select Case s
    Case "p"
' Pone in pausa la riproduzione del file mediale:
      gst_element_set_state(audio, GST_STATE_PAUSED)
    Case "r"
' Riprende la riproduzione del file mediale:
      gst_element_set_state(audio, GST_STATE_PLAYING)
    Case "s"
' Arresta la riproduzione del file mediale:
      gst_element_set_state(audio, GST_STATE_NULL)
      Termina()
  End Select
  
End


Private Procedure Termina()

  gst_object_unref(audio)
  Print "\nEsecuzione terminata."
  Quit
  
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(): 

Private audio As Pointer


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
 
' gboolean gst_element_query_position(GstElement * element, GstFormat format, gint64 * cur)
' Queries an element For the stream position In nanoseconds.
Private Extern gst_element_query_position(gstelement As Pointer, gstformat As Pointer, cur 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 pos, dur As Long
 Dim po, du As Date
     
  gst_init(0, 0)
  
  audio = gst_parse_launch("filesrc location=/percorso/del/file/audio ! decodebin ! tee name=t " &
                           "! queue ! audioconvert ! monoscope ! ximagesink ! queue ! m. t. ! queue ! autoaudiosink", 0)
                
' Avviamo l'esecuzione del file audio:
  gst_element_set_state(audio, GST_STATE_PLAYING)
  
  While True
    gst_element_query_position(audio, GST_FORMAT_TIME, VarPtr(pos))
    gst_element_query_duration(audio, GST_FORMAT_TIME, VarPtr(dur))
    po = Date(0, 0, 0, 0, 0, 0, pos / 1000000)
    du = Date(0, 0, 0, 0, 0, 0, dur / 1000000)
    If (pos > 0) And (CStr(po) >= CStr(du)) Then Break
    Write #File.Out, "\rDurata: " & du & "      " & "Tempo trascorso: " & po
  Wend
  
  Termina()
        
End


Public Sub Application_Read()
  
 Dim s As String
 
  Input #File.In, s
  
  Select Case s
    Case "p"
' Pone in pausa la riproduzione del file mediale:
      gst_element_set_state(audio, GST_STATE_PAUSED)
    Case "r"
' Riprende la riproduzione del file mediale:
      gst_element_set_state(audio, GST_STATE_PLAYING)
    Case "s"
' Arresta la riproduzione del file mediale:
      gst_element_set_state(audio, GST_STATE_NULL)
      Termina()
  End Select
  
End


Private Procedure Termina()

  gst_object_unref(audio)
  Print "\nEsecuzione terminata."
  Quit
  
End



Riferimenti

Estratto da "https://www.gambas-it.org/wiki/index.php?title=Visualizzare_un_oscilloscopio_di_GStreamer_mediante_la_funzione_%27gst_parse_launch()%27_durante_l%27esecuzione_di_un_file_audio&oldid=19922"