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79 lines
2.3 KiB
XML
79 lines
2.3 KiB
XML
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<!-- ############ chapter ############# -->
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<chapter id="chapter-building-eventfn">
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<title>The event function</title>
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<para>
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The event function notifies you of special events that happen in
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the datastream (such as caps, end-of-stream, newsegment, tags, etc.).
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Events can travel both upstream and downstream, so you can receive them
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on sink pads as well as source pads.
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</para>
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<para>
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Below follows a very simple event function that we install on the sink
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pad of our element.
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</para>
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<programlisting><!-- example-begin event.c a --><!--
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#include "init.func"
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#include "caps.func"
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static gboolean
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gst_my_filter_event (GstPad * pad, GstObject * parent, GstEvent * event)
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{
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return gst_pad_event_default (pad, parent, event);
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}
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--><!-- example-end event.c a -->
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static gboolean gst_my_filter_sink_event (GstPad *pad,
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GstObject *parent,
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GstBuffer *buf);
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[..]
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static void
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gst_my_filter_init (GstMyFilter * filter)
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{
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[..]
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/* configure event function on the pad before adding
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* the pad to the element */
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gst_pad_set_event_function (filter->sinkpad,
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gst_my_filter_sink_event);
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[..]
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}
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static gboolean
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gst_my_filter_sink_event (GstPad *pad,
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GstObject *parent,
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GstEvent *event)
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{
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gboolean ret;
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GstMyFilter *filter = GST_MY_FILTER (parent);
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switch (GST_EVENT_TYPE (event)) {
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case GST_EVENT_CAPS:
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/* we should handle the format here */
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/* push the event downstream */
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ret = gst_pad_push_event (filter->srcpad, event);
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break;
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case GST_EVENT_EOS:
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/* end-of-stream, we should close down all stream leftovers here */
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gst_my_filter_stop_processing (filter);
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ret = gst_pad_event_default (pad, parent, event);
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break;
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default:
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/* just call the default handler */
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ret = gst_pad_event_default (pad, parent, event);
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break;
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}
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return ret;
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}
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</programlisting>
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<para>
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It is a good idea to call the default event handler
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<function>gst_pad_event_default ()</function> for unknown events.
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Depending on the event type, the default handler will forward
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the event or simply unref it. The CAPS event is by default not
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forwarded so we need to do this in the event handler ourselves.
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</para>
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</chapter>
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