Differenze tra le versioni di "Riproduzione dell'audio di radio WEB con le funzioni esterne del API di GStreamer"

Versione delle 16:29, 16 feb 2017

Le stazioni radio via WEB possono essere ascoltate utilizzando le risorse del API di GStreamer.

Uso del plug-in playbin

Private play As Pointer

Library "libgstreamer-1.0"

Private Const GST_STATE_NULL As Integer = 1
Private Const GST_STATE_PLAYING As Integer = 4

' gst_init (&argc, &argv)
' Initializes the GStreamer library, setting up internal path lists, registering built-in elements, and loading standard plugins.
Private Extern gst_init(argc As Integer, argv As Pointer)

' GstElement * gst_element_factory_make(const gchar *factoryname, Const gchar * name)
' Create a new element of the type defined by the given element factory.
Private Extern gst_element_factory_make(factoryname As String, name As String) As Pointer

' void g_object_set(gpointer object, const gchar *first_property_name, ...)
' Sets properties on an object.
Private Extern g_object_set(gobject As Pointer, key As String, value As String, nl As String)

' GstStateChangeReturn gst_element_set_state(GstElement *element, GstState state)
' Sets the state of the element.
Private Extern gst_element_set_state(gstobject As Pointer, state As Integer) As Integer

' void gst_object_unref(gpointer object)
' Decrements the reference count on object .
Private Extern gst_object_unref(gobject As Pointer)


Public Sub Form_Open()

Dim retI As Integer

 gst_init(0, 0)

 play = gst_element_factory_make("playbin", "play")

' Nel terzo argomento della seguente funzione va inserito
' l'indirizzo web del flusso di dati audio in tempo reale:
 g_object_set(play, "uri", "http://indirizzo/web/del/flusso/dati/della/radio4-web", Null)

' Avviamo la riproduzione audio della radio-web:
 retI = gst_element_set_state(play, GST_STATE_PLAYING)
 Print "Stato di cambiamento = "; retI

End


Public Sub Button1_Click()

Dim retI As Integer

' Arrestiamo la riproduzione audio:
 retI = gst_element_set_state(play, GST_STATE_NULL)
 Print "Stato di cambiamento = "; retI
  
 gst_object_unref(play)

End

Uso della funzione gst_parse_launch( ) e del plugin jackaudiosink

Per l'esecuzione del seguente codice è necessario avviare preliminarmente il programma Jack.

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_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 audio As Pointer
 Dim pos As Long
 Dim po As Date
    
  gst_init(0, 0)
  
  audio = gst_parse_launch("uridecodebin uri=http://indirizzo/della/radio/web/live ! audioconvert ! audioresample ! jackaudiosink", 0)
      
' Avviamo l'esecuzione audio della radio web:
  gst_element_set_state(audio, GST_STATE_PLAYING)
  
  While True
    gst_element_query_position(audio, GST_FORMAT_TIME, VarPtr(pos))
    po = Date(0, 0, 0, 0, 0, 0, pos / 1000000)
    Write #File.Out, "\rTempo trascorso: " & po
  Wend
  
  gst_object_unref(audio)
     
End