Visualizza wikitesto di Analizzare il valore RMS, il picco e il decay dei dati audio mediante il plugin 'level'usando una linea di pipeline con la funzione 'gst parse launch()'

Il plug-in ''Level'' fornito dalla libreria ''GStreamer'' analizza i buffer audio in arrivo e, se la proprietà "message" è vera, esso genera un messaggio denominato "''Element''", dal quale è possibile estrarre alcuni valori attinente ai dati audio medesimi, come ad esempio il valore ''RMS'', il valore di ''picco'' e il valore di ''decay''.

E' necessario avere installata nel proprio sistema e richiamare nel progetto Gambas la libreria dinamica condivisa: "''libgstreamer-1.0.so''"

Mostriamo di seguito un semplice esempio, nel quale verranno analizzati i dati audio di un file WAV:
 Library "libgstreamer-1.0"
 
 Public Struct GValueArray
   n_values As Integer
   values As Pointer
 End Struct
 
 Private Enum GST_STATE_VOID_PENDING = 0, GST_STATE_NULL, GST_STATE_READY, GST_STATE_PAUSED, GST_STATE_PLAYING
 Private Const GST_MESSAGE_ERROR As Integer = 2
 Private Const GST_MESSAGE_ELEMENT As Integer = 32768
 
 <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>' ''GMainLoop * g_main_loop_new (GMainContext *context, gboolean is_running)''
 ' ''Creates a new GMainLoop structure.''</font>
 Private Extern g_main_loop_new(context As Pointer, is_running As Boolean) 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>' ''GstBus * gst_pipeline_get_bus (GstPipeline *pipeline)''
 ' ''Gets the GstBus of pipeline.''</font>
 Private Extern gst_pipeline_get_bus(pipeline As Pointer) As Pointer
 
 <FONT Color=gray>' ''guint gst_bus_add_watch (GstBus *bus, GstBusFunc func, gpointer user_data)''
 ' ''Adds a bus watch to the default main context with the default priority.''</font>
 Private Extern gst_bus_add_watch(bus As Pointer, func As Pointer, user_data As Pointer) As Integer
 
 <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(element As Pointer, state As Integer) As Integer
 
 <FONT Color=gray>' ''void g_main_loop_run (GMainLoop *loop)''
 ' ''Runs a main loop until g_main_loop_quit() is called on the loop.''</font>
 Private Extern g_main_loop_run(gloop As Pointer)
 
 <FONT Color=gray>' ''const gchar * gst_structure_get_name (const GstStructure *structure)''
 ' ''Get the name of structure as a string.''</font>
 Private Extern gst_structure_get_name(gstructure As Pointer) As String
 
 <FONT Color=gray>' ''const GstStructure * gst_message_get_structure (GstMessage *message)''
 ' ''Access the structure of the message.''</font>
 Private Extern gst_message_get_structure(message As Pointer) As Pointer
 
 <FONT Color=gray>' ''gpointer g_value_get_boxed (const GValue *value)''
 ' ''Get the contents of a G_TYPE_BOXED derived GValue.''</font>
 Private Extern g_value_get_boxed(value As Pointer) As Pointer
 
 <FONT Color=gray>' ''const GValue * gst_structure_get_value (const GstStructure *structure, const gchar *fieldname)''
 ' ''Get the value of the field with name fieldname.''</font>
 Private Extern gst_structure_get_value(gstructure As Pointer, fieldname As String) As Pointer
 
 <FONT Color=gray>' ''GValue * g_value_array_get_nth (GValueArray *value_array, guint index_)''
 ' ''Return a pointer to the value at index_ containd in value_array.''</font>
 Private Extern g_value_array_get_nth(value_array As GValueArray, index As Integer) As Pointer
 
 <FONT Color=gray>' ''gdouble g_value_get_double (const GValue *value)''
 ' ''Get the contents of a G_TYPE_DOUBLE GValue.''</font>
 Private Extern g_value_get_double(value As Pointer) As Float
 
 <FONT Color=gray>' ''gboolean gst_structure_get_clock_time (const GstStructure *structure, const gchar *fieldname, GstClockTime *value)''
 ' ''Sets the clock time pointed to by value corresponding to the clock time of the given field.''</font>
 Private Extern gst_structure_get_clock_time(gstructure As Pointer, fieldname As String, value 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 lp, lev, bs As Pointer
  Dim fileaudio As String
  
   fileaudio = <FONT Color=gray>''/percorso/del/file.wav''</font>
    
   gst_init(0, 0)
   
   lp = g_main_loop_new(0, False)
   
 <FONT Color=gray>' ''Imposta gli elementi necessari per l'analisi del file audio:''</font>
   lev = gst_parse_launch("filesrc location=" & fileaudio & " ! wavparse ! audioconvert ! <FONT Color=#B22222>level</font> ! audio/x-raw,channels=2 ! fakesink", 0)
   
 <FONT Color=gray>' ''Poiché l'elemento "level" inserisce i propri risultati nel puntatore "GstBus", è necessario estrapolarlo dalla pipeline:''</font>
   bs = gst_pipeline_get_bus(lev)
   
 <FONT Color=gray>' ''Resta in osservazione se è pronto un messaggio nel bus, nel qual caso invoca la funzione "Gestione_messaggio_bus()":''</font>
  Print gst_bus_add_watch(bs, Gestione_messaggio_bus, lp)
   
 <FONT Color=gray>' ''Avvia l'analisi del file audio:''</font>
   gst_element_set_state(lev, GST_STATE_PLAYING)
   
 <FONT Color=gray>' ''Avvia un loop infinito:''</font>
   g_main_loop_run(lp)
   
 '''End'''
 
 
 '''Public''' Function Gestione_messaggio_bus(bus As Pointer, msg As Pointer, data As Pointer) As Boolean
  
  Dim gst, GValue As Pointer
  Dim rms, rms_dB, peak_dB, decay_dB As Float
  Dim rms_arr, peak_arr, decay_arr As GValueArray
  Dim channels, i As Integer
  Dim endtime As Long
   
   Select Case Int@(msg + 64)        <FONT Color=gray>' ''GstMessage->type''</font>
     Case GST_MESSAGE_ELEMENT
       gst = gst_message_get_structure(msg)
       If gst_structure_get_name(gst) = "level" Then
       rms_arr = g_value_get_boxed(gst_structure_get_value(gst, "rms"))
       peak_arr = g_value_get_boxed(gst_structure_get_value(gst, "peak"))
       decay_arr = g_value_get_boxed(gst_structure_get_value(gst, "decay"))
       channels = rms_arr.n_values
       
       Print "Numero canali audio: "; channels
       
       For i = 0 To channels - 1
         Print "Canale: "; i
         GValue = g_value_array_get_nth(rms_arr, i)
         rms_dB = g_value_get_double(GValue)
          
         GValue = g_value_array_get_nth(peak_arr, i)
         peak_dB = g_value_get_double(GValue)
         
         GValue = g_value_array_get_nth(decay_arr, i)
         decay_dB = g_value_get_double(GValue)
         Print "    RMS: "; rms_dB; " dB, picco: "; peak_dB; " dB, decay: "; decay_dB; " dB"
         
 <FONT Color=gray>' ''Converte da dB a normale dando un valore compreso tra 0,0 e 1,0:''</font>
         rms = (10 ^ (rms_dB / 20))
         Print "    Valore rms normalizzato: "; rms
         
         If gst_structure_get_clock_time(gst, "endtime", VarPtr(endtime)) = False Then
           Print "Attenzione: impossibile analizzare 'endtime' !"
         Else
           Print "endtime: "; CStr(Date(0, 0, 0, 0, 0, 0, CInt(endtime / 1000000)))
         Endif
         Wait 0.001
         Print
       Next
       Endif
     Case GST_MESSAGE_ERROR
       Print "Errore durante l'analisi del file audio !"
   End Select
   
   Return True
   
 '''End'''




=Riferimenti=
* https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-good/html/gst-plugins-good-plugins-level.html