mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-12-27 02:30:35 +00:00
112 lines
3.2 KiB
Markdown
112 lines
3.2 KiB
Markdown
---
|
|
title: The chain function
|
|
...
|
|
|
|
# The chain function
|
|
|
|
The chain function is the function in which all data processing takes
|
|
place. In the case of a simple filter, `_chain ()` functions are mostly
|
|
linear functions - so for each incoming buffer, one buffer will go out,
|
|
too. Below is a very simple implementation of a chain function:
|
|
|
|
``` c
|
|
|
|
static GstFlowReturn gst_my_filter_chain (GstPad *pad,
|
|
GstObject *parent,
|
|
GstBuffer *buf);
|
|
|
|
[..]
|
|
|
|
static void
|
|
gst_my_filter_init (GstMyFilter * filter)
|
|
{
|
|
[..]
|
|
/* configure chain function on the pad before adding
|
|
* the pad to the element */
|
|
gst_pad_set_chain_function (filter->sinkpad,
|
|
gst_my_filter_chain);
|
|
[..]
|
|
}
|
|
|
|
static GstFlowReturn
|
|
gst_my_filter_chain (GstPad *pad,
|
|
GstObject *parent,
|
|
GstBuffer *buf)
|
|
{
|
|
GstMyFilter *filter = GST_MY_FILTER (parent);
|
|
|
|
if (!filter->silent)
|
|
g_print ("Have data of size %" G_GSIZE_FORMAT" bytes!\n",
|
|
gst_buffer_get_size (buf));
|
|
|
|
return gst_pad_push (filter->srcpad, buf);
|
|
}
|
|
```
|
|
|
|
Obviously, the above doesn't do much useful. Instead of printing that
|
|
the data is in, you would normally process the data there. Remember,
|
|
however, that buffers are not always writeable.
|
|
|
|
In more advanced elements (the ones that do event processing), you may
|
|
want to additionally specify an event handling function, which will be
|
|
called when stream-events are sent (such as caps, end-of-stream,
|
|
newsegment, tags, etc.).
|
|
|
|
static void
|
|
gst_my_filter_init (GstMyFilter * filter)
|
|
{
|
|
[..]
|
|
gst_pad_set_event_function (filter->sinkpad,
|
|
gst_my_filter_sink_event);
|
|
[..]
|
|
}
|
|
|
|
|
|
|
|
static gboolean
|
|
gst_my_filter_sink_event (GstPad *pad,
|
|
GstObject *parent,
|
|
GstEvent *event)
|
|
{
|
|
GstMyFilter *filter = GST_MY_FILTER (parent);
|
|
|
|
switch (GST_EVENT_TYPE (event)) {
|
|
case GST_EVENT_CAPS:
|
|
/* we should handle the format here */
|
|
break;
|
|
case GST_EVENT_EOS:
|
|
/* end-of-stream, we should close down all stream leftovers here */
|
|
gst_my_filter_stop_processing (filter);
|
|
break;
|
|
default:
|
|
break;
|
|
}
|
|
|
|
return gst_pad_event_default (pad, parent, event);
|
|
}
|
|
|
|
static GstFlowReturn
|
|
gst_my_filter_chain (GstPad *pad,
|
|
GstObject *parent,
|
|
GstBuffer *buf)
|
|
{
|
|
GstMyFilter *filter = GST_MY_FILTER (parent);
|
|
GstBuffer *outbuf;
|
|
|
|
outbuf = gst_my_filter_process_data (filter, buf);
|
|
gst_buffer_unref (buf);
|
|
if (!outbuf) {
|
|
/* something went wrong - signal an error */
|
|
GST_ELEMENT_ERROR (GST_ELEMENT (filter), STREAM, FAILED, (NULL), (NULL));
|
|
return GST_FLOW_ERROR;
|
|
}
|
|
|
|
return gst_pad_push (filter->srcpad, outbuf);
|
|
}
|
|
|
|
In some cases, it might be useful for an element to have control over
|
|
the input data rate, too. In that case, you probably want to write a
|
|
so-called *loop-based* element. Source elements (with only source pads)
|
|
can also be *get-based* elements. These concepts will be explained in
|
|
the advanced section of this guide, and in the section that specifically
|
|
discusses source pads.
|