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>Chapter 20. Events: Seeking, Navigation and More</H1
><P
> There are many different event types but only 2 ways they can travel accross
the pipeline: downstream or upstream. It is very important to understand
how both of those methods work because if one element in the pipeline is not
handling them correctly the whole event system of the pipeline is broken.
We will try to explain here how these methods work and how elements are
supposed to implement them.
</P
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NAME="section-events-downstream"
>20.1. Downstream events</A
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><P
> Downstream events are received through the sink pad's dataflow. Depending
if your element is loop or chain based you will receive events in your
loop/chain function as a GstData with <CODE
CLASS="function"
>gst_pad_pull</CODE
>
or directly in the function call arguments. So when receiving dataflow
from the sink pad you have to check first if this data chunk is an event.
If that's the case you check what kind of event it is to react on relevant
ones and then forward others dowstream using
<CODE
CLASS="function"
>gst_pad_event_default</CODE
>. Here is an example for both
loop and chain based elements.
</P
><PRE
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> /* Chain based element */
static void
gst_my_filter_chain (GstPad *pad,
GstData *data)
{
GstMyFilter *filter = GST_MY_FILTER (gst_pad_get_parent (pad));
...
if (GST_IS_EVENT (data)) {
GstEvent *event = GST_EVENT (data);
switch (GST_EVENT_TYPE (event)) {
case GST_EVENT_EOS:
/* end-of-stream, we should close down all stream leftovers here */
gst_my_filter_stop_processing (filter);
/* fall-through to default event handling */
default:
gst_pad_event_default (pad, event);
break;
}
return;
}
...
}
/* Loop based element */
static void
gst_my_filter_loop (GstElement *element)
{
GstMyFilter *filter = GST_MY_FILTER (element);
GstData *data = NULL;
data = gst_pad_pull (filter->sinkpad);
if (GST_IS_EVENT (data)) {
GstEvent *event = GST_EVENT (data);
switch (GST_EVENT_TYPE (event)) {
case GST_EVENT_EOS:
/* end-of-stream, we should close down all stream leftovers here */
gst_my_filter_stop_processing (filter);
/* fall-through to default event handling */
default:
gst_pad_event_default (filter->sinkpad, event);
break;
}
return;
}
...
}
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