Visualizza wikitesto di Estrarre tutte le tracce di un CD audio convertendole in un unico file MP3 con la funzione 'gst parse launch()' di GStreamer

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.so.0.2407.0'' ".


Mostriamo un esempio pratico, nel quale verranno estratte e convertite in un unico file MP3 tutte le tracce di un CD audio:
 Library "libgstreamer-1.0:0.2407.0"
 
 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 pos, dur As Long
   Dim po, du As Date
  
   gst_init(0, 0)
   
   audio = gst_parse_launch("cdparanoiasrc <FONT Color=red>mode=continuous</font> ! audioconvert ! lamemp3enc target=bitrate cbr=true bitrate=192 ! filesink location=<FONT Color=darkgreen>''/percorso/del/file.mp3''</font>", 0)
        
 <FONT Color=gray>' ''Avviamo l'estrazione e la conversione dell'intero CD audio:''</font>
   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 "\rDurata: " & du & "      " & "Tempo trascorso: " & po
     Wait 0.01
   Wend
   
    
   gst_object_unref(audio)
   Print "\nEstrazione e conversione terminata."
   Quit
    
 End