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Add probe example.
Original commit message from CVS: * docs/manual/advanced-dataaccess.xml: * examples/manual/Makefile.am: Add probe example. * gst/gstpad.c: (_gst_do_pass_data_accumulator): Make work (??).
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Ronald S. Bultje
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5 changed files with 109 additions and 15 deletions
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@ -1,3 +1,11 @@
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2005-06-29 Ronald S. Bultje <rbultje@ronald.bitfreak.net>
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* docs/manual/advanced-dataaccess.xml:
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* examples/manual/Makefile.am:
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Add probe example.
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* gst/gstpad.c: (_gst_do_pass_data_accumulator):
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Make work (??).
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2005-06-29 Tim-Philipp Müller <tim at centricular dot net>
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* gst/elements/gstfilesink.c: (gst_filesink_render):
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@ -14,16 +14,100 @@
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</para>
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<sect1 id="section-data-probe">
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<title>Data probes</title>
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<title>Data probing</title>
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<para>
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Probes are best envisioned as pad listeners. They are attached to a
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pad in a pipeline, and you can add callback functions to this probe.
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Those callback functions will be called whenever data is being sent
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over this pad. The callback can then decide whether the data should
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be discarded or it can replace the piece of data with another piece
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of data. In this callback, it can also trigger actions in the
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application itself. For pipeline manipulation, probes are rather
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limited, but for pipeline tracking, they can be very useful.
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Probing is best envisioned as a pad listener. Technically, a probe is
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nothing more than a signal callback that can be attached to a pad.
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Those signals are by default not fired at all (since that may have a
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negative impact on performance), but can be enabled by attaching a
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probe using <function>gst_pad_add_data_probe ()</function> or one of
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the similar functions. Those functions attach the signal handler and
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enable the actual signal emission. Similarly, one can use the
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<function>gst_pad_remove_data_probe ()</function> or related functions
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to remove the signal handlers again. It is also possible to only listen
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to events or only to buffers (and ignore the other).
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</para>
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<para>
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Probes run in pipeline threading context, so callbacks should try to
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not block and generally not do any weird stuff, since this could
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have a negative impact on pipeline performance or, in case of bugs,
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cause deadlocks or crashes. However, most common buffer operations
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that elements can do in <function>_chain ()</function> functions, can
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be done in probe callbacks as well. The example below gives a short
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impression on how to use them.
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</para>
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<programlisting><!-- example-begin probe.c -->
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#include <gst/gst.h>
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static gboolean
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cb_have_data (GstPad *pad,
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GstBuffer *buffer,
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gpointer u_data)
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{
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gint x, y;
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guint16 *data = (guint16 *) GST_BUFFER_DATA (buffer), t;
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/* invert data */
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for (y = 0; y < 288; y++) {
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for (x = 0; x < 384 / 2; x++) {
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t = data[384 - 1 - x];
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data[384 - 1 - x] = data[x];
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data[x] = t;
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}
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data += 384;
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}
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return TRUE;
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}
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gint
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main (gint argc,
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gchar *argv[])
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{
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GMainLoop *loop;
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GstElement *pipeline, *src, *sink, *filter, *csp;
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GstPad *pad;
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/* init GStreamer */
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gst_init (&argc, &argv);
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loop = g_main_loop_new (NULL, FALSE);
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/* build */
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pipeline = gst_pipeline_new ("my-pipeline");
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src = gst_element_factory_make ("videotestsrc", "src");
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filter = gst_element_factory_make ("capsfilter", "filter");
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csp = gst_element_factory_make ("ffmpegcolorspace", "csp");
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sink = gst_element_factory_make ("xvimagesink", "sink");
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gst_element_link_many (src, filter, csp, sink, NULL);
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gst_bin_add_many (GST_BIN (pipeline), src, filter, csp, sink, NULL);
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g_object_set (G_OBJECT (filter), "filter-caps",
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gst_caps_new_simple ("video/x-raw-rgb",
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"width", G_TYPE_INT, 384,
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"height", G_TYPE_INT, 288,
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"framerate", G_TYPE_DOUBLE, (gdouble) 25.0,
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"bpp", G_TYPE_INT, 16,
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"depth", G_TYPE_INT, 16,
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"endianness", G_TYPE_INT, G_BYTE_ORDER,
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NULL), NULL);
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pad = gst_element_get_pad (src, "src");
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gst_pad_add_buffer_probe (pad, G_CALLBACK (cb_have_data), NULL);
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gst_object_unref (pad);
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/* run */
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gst_element_set_state (pipeline, GST_STATE_PLAYING);
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g_main_loop_run (loop);
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/* exit */
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gst_element_set_state (pipeline, GST_STATE_NULL);
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gst_object_unref (pipeline);
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return 0;
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}
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<!-- example-end probe.c --></programlisting>
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<para>
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Compare that output with the output of <quote>gst-launch-0.9
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videotestsrc ! xvimagesink</quote>, just so you know what you're
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looking for.
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</para>
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</sect1>
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@ -36,6 +36,7 @@ EXAMPLES = \
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popt \
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query \
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typefind \
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probe \
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fakesrc \
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playbin \
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decodebin \
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@ -77,7 +78,7 @@ typefind.c dynamic.c: $(top_srcdir)/docs/manual/advanced-autoplugging.xml
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$(PERL_PATH) $(srcdir)/extract.pl $@ \
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$(top_srcdir)/docs/manual/advanced-autoplugging.xml
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fakesrc.c: $(top_srcdir)/docs/manual/advanced-dataaccess.xml
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probe.c fakesrc.c: $(top_srcdir)/docs/manual/advanced-dataaccess.xml
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$(PERL_PATH) $(srcdir)/extract.pl $@ \
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$(top_srcdir)/docs/manual/advanced-dataaccess.xml
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@ -125,11 +125,11 @@ static gboolean
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_gst_do_pass_data_accumulator (GSignalInvocationHint * ihint,
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GValue * return_accu, const GValue * handler_return, gpointer dummy)
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{
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if (!g_value_get_boolean (handler_return)) {
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g_value_set_boolean (return_accu, FALSE);
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if (ihint->run_type == G_SIGNAL_RUN_FIRST) {
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gboolean ret = g_value_get_boolean (handler_return);
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/* stop emission here */
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return FALSE;
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g_value_set_boolean (return_accu, ret);
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return ret;
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}
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return TRUE;
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@ -36,6 +36,7 @@ EXAMPLES = \
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popt \
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query \
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typefind \
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probe \
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fakesrc \
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playbin \
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decodebin \
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@ -77,7 +78,7 @@ typefind.c dynamic.c: $(top_srcdir)/docs/manual/advanced-autoplugging.xml
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$(PERL_PATH) $(srcdir)/extract.pl $@ \
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$(top_srcdir)/docs/manual/advanced-autoplugging.xml
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fakesrc.c: $(top_srcdir)/docs/manual/advanced-dataaccess.xml
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probe.c fakesrc.c: $(top_srcdir)/docs/manual/advanced-dataaccess.xml
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$(PERL_PATH) $(srcdir)/extract.pl $@ \
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$(top_srcdir)/docs/manual/advanced-dataaccess.xml
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