Eseguire una traccia di un CD audio mediante la funzione 'gst parse launch()' di GStreamer
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.
Sarà necessario avere installata nel sistema e richiamare nell'applicazione Gambas la libreria dinamica condivisa: "libgstreamer-1.0"
Mostriamo un esempio pratico per eseguire una traccia di un CD audio:
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("playbin uri=cdda://numero_della_traccia", 0)
' Avviamo la riproduzione 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 della traccia audio:
gst_element_set_state(audio, GST_STATE_PAUSED)
Case "r"
' Riprende la riproduzione della traccia audio:
gst_element_set_state(audio, GST_STATE_PLAYING)
Case "s"
' Arresta la riproduzione della traccia audio:
gst_element_set_state(audio, GST_STATE_NULL)
Termina()
End Select
End
Private Procedure Termina()
gst_object_unref(audio)
Print "\nEsecuzione terminata."
Quit
End
