Visualizza wikitesto di Visualizzare uno spettroscopio di GStreamer mediante la funzione 'gst parse launch()' durante l'esecuzione di un file audio

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 condivisa: "''libgstreamer-1.0'' ".

Usando i plugin "''spectrascope''" e "''autoaudiosink''" all'interno della riga della ''pipeline'' della funzione "gst_parse_launch()", è possibile visualizzare uno spettroscopio attivo durante l'esecuzione di un file audio di formato WAV, MP3 e OGG.

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
  
 <FONT Color=gray>' ''gst_init (int *argc, char **argv[])''
 ' ''Initializes the GStreamer library, setting up internal path lists, registering built-in elements, and loading standard plugins.''</font>
 Private Extern gst_init(argc As Pointer, argv As Pointer)
 
 <FONT Color=gray>' ''GstElement * gst_parse_launch (const gchar *pipeline_description, GError **error)''
 ' ''Create a new pipeline based on command line syntax.''</font>
 Private Extern gst_parse_launch(description As String, GError As Pointer) As Pointer
 
 <FONT Color=gray>' ''GstStateChangeReturn gst_element_set_state(GstElement *element, GstState state)''
 ' ''Sets the state of the element.''</font>
 Private Extern gst_element_set_state(gstelement As Pointer, state As Integer) As Integer
 
 <FONT Color=gray>' ''gboolean gst_element_query_duration(GstElement * element, GstFormat format, gint64 * duration)''
 ' ''Queries an element For the total stream duration In nanoseconds.''</font>
 Private Extern gst_element_query_duration(gselement As Pointer, formatI As Integer, duration As Pointer) As Boolean
  
 <FONT Color=gray>' ''gboolean gst_element_query_position(GstElement * element, GstFormat format, gint64 * cur)''
 ' ''Queries an element For the stream position In nanoseconds.''</font>
 Private Extern gst_element_query_position(gstelement As Pointer, gstformat As Pointer, cur As Pointer) As Boolean
  
 <FONT Color=gray>' ''void gst_object_unref(gpointer object)''
 ' ''Decrements the reference count on object.''</font>
 Private Extern gst_object_unref(gobject As Pointer)
 
 
 Public Sub Main()
  
  Dim audio As Pointer
  Dim durata, pos, As Long
 
  gst_init(0, 0)
   
  audio = gst_parse_launch("filesrc location=<FONT Color=darkgreen>''/percorso/del/file/audio''</font> ! decodebin ! tee name=t " &
                           "! queue ! audioconvert ! spectrascope ! video/x-raw, width=1000, height=500! videoconvert " &
                           "! autovideosink ! queue ! audioconvert! m. t. ! queue ! autoaudiosink", 0)
              
 <FONT Color=gray>' ''Avviamo l'esecuzione del file audio:''</font>
  gst_element_set_state(audio, GST_STATE_PLAYING)
 
  Repeat
    gst_element_query_duration(elem, GST_FORMAT_TIME, VarPtr(durata))
    Wait 0.01
  Until durata > -1
 
  Repeat
    gst_element_query_position(elem, GST_FORMAT_TIME, VarPtr(pos))
    Write "\r\e[0mDurata: " & Time(0, 0, 0, durata / 1000000) & "      Pos. \e[31m" & Time(0, 0, 0, pos / 1000000)
    Wait 0.001
  Until pos >= durata
 
  gst_object_unref(audio)
  Print "\nEsecuzione terminata."
  Quit
  
 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-spectrascope.html
* http://gstreamer.freedesktop.org/
* http://gstreamer.com/