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pwg: more updates for 1.0

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This commit is contained in:
Wim Taymans 2012-09-27 13:57:46 +02:00
parent 2d0c1572fb
commit b527b0b498
4 changed files with 166 additions and 144 deletions
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54
docs/pwg/building-chainfn.xml
View file

@ -14,20 +14,39 @@
#include "init.func"
#include "caps.func"
static gboolean
gst_my_filter_event (GstPad * pad, GstEvent * event)
gst_my_filter_event (GstPad * pad, GstObject * parent, GstEvent * event)
{
return gst_pad_event_default (pad, event);
return gst_pad_event_default (pad, parent, event);
}
--><!-- example-end chain.c a -->
<!-- example-begin chain.c b -->
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-&gt;sinkpad,
gst_my_filter_chain);
[..]
}
static GstFlowReturn
gst_my_filter_chain (GstPad *pad,
GstObject *parent,
GstBuffer *buf)
{
GstMyFilter *filter = GST_MY_FILTER (GST_OBJECT_PARENT (pad));
GstMyFilter *filter = GST_MY_FILTER (parent);
if (!filter->silent)
g_print ("Have data of size %u bytes!\n", GST_BUFFER_SIZE (buf));
g_print ("Have data of size %" G_GSIZE_FORMAT" bytes!\n",
gst_buffer_get_size (buf));
return gst_pad_push (filter->srcpad, buf);
}
@ -44,10 +63,12 @@ gst_my_filter_change_state (GstElement * element, GstStateChange transition)
<para>
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 end-of-stream, newsegment, tags, etc.).
that buffers are not always writeable.
</para>
<para>
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.).
</para>
<programlisting>
static void
@ -55,7 +76,7 @@ gst_my_filter_init (GstMyFilter * filter)
{
[..]
gst_pad_set_event_function (filter-&gt;sinkpad,
gst_my_filter_event);
gst_my_filter_sink_event);
[..]
}
<!-- example-begin chain2.c a --><!--
@ -77,12 +98,16 @@ gst_my_filter_process_data (GstMyFilter * filter, const GstBuffer * buf)
--><!-- example-end chain.func a -->
<!-- example-begin chain.func b -->
static gboolean
gst_my_filter_event (GstPad *pad,
GstEvent *event)
gst_my_filter_sink_event (GstPad *pad,
GstObject *parent,
GstEvent *event)
{
GstMyFilter *filter = GST_MY_FILTER (GST_OBJECT_PARENT (pad));
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);
@ -91,14 +116,15 @@ gst_my_filter_event (GstPad *pad,
break;
}
return gst_pad_event_default (pad, event);
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 (gst_pad_get_parent (pad));
GstMyFilter *filter = GST_MY_FILTER (parent);
GstBuffer *outbuf;
outbuf = gst_my_filter_process_data (filter, buf);

78
docs/pwg/building-eventfn.xml Normal file
View file

@ -0,0 +1,78 @@
<!-- ############ chapter ############# -->
<chapter id="chapter-building-eventfn">
<title>The event function</title>
<para>
The event function notifies you of special events that happen in
the datastream (such as caps, end-of-stream, newsegment, tags, etc.).
Events can travel both upstream and downstream, so you can receive them
on sink pads as well as source pads.
</para>
<para>
Below follows a very simple event function that we install on the sink
pad of our element.
</para>
<programlisting><!-- example-begin event.c a --><!--
#include "init.func"
#include "caps.func"
static gboolean
gst_my_filter_event (GstPad * pad, GstObject * parent, GstEvent * event)
{
return gst_pad_event_default (pad, parent, event);
}
--><!-- example-end event.c a -->
static gboolean gst_my_filter_sink_event (GstPad *pad,
GstObject *parent,
GstBuffer *buf);
[..]
static void
gst_my_filter_init (GstMyFilter * filter)
{
[..]
/* configure event function on the pad before adding
* the pad to the element */
gst_pad_set_event_function (filter-&gt;sinkpad,
gst_my_filter_sink_event);
[..]
}
static gboolean
gst_my_filter_sink_event (GstPad *pad,
GstObject *parent,
GstEvent *event)
{
gboolean ret;
GstMyFilter *filter = GST_MY_FILTER (parent);
switch (GST_EVENT_TYPE (event)) {
case GST_EVENT_CAPS:
/* we should handle the format here */
/* push the event downstream */
ret = gst_pad_push_event (filter->srcpad, event);
break;
case GST_EVENT_EOS:
/* end-of-stream, we should close down all stream leftovers here */
gst_my_filter_stop_processing (filter);
ret = gst_pad_event_default (pad, parent, event);
break;
default:
/* just call the default handler */
ret = gst_pad_event_default (pad, parent, event);
break;
}
return ret;
}
</programlisting>
<para>
It is a good idea to call the default event handler
<function>gst_pad_event_default ()</function> for unknown events.
Depending on the event type, the default handler will forward
the event or simply unref it. The CAPS event is by default not
forwarded so we need to do this in the event handler ourselves.
</para>
</chapter>

176
docs/pwg/building-pads.xml
View file

@ -8,17 +8,18 @@
of your element, and that makes them a very important item in the process
of element creation. In the boilerplate code, we have seen how static pad
templates take care of registering pad templates with the element class.
Here, we will see how to create actual elements, use a <function>_setcaps
()</function>-functions to configure for a particular format and how to
Here, we will see how to create actual elements, use an <function>_event
()</function>-function to configure for a particular format and how to
register functions to let data flow through the element.
</para>
<para>
In the element <function>_init ()</function> function, you create the pad
from the pad template that has been registered with the element class in
the <function>_base_init ()</function> function. After creating the pad,
you have to set a <function>_setcaps ()</function> function pointer and
optionally a <function>_getcaps ()</function> function pointer. Also, you
have to set a <function>_chain ()</function> function pointer.
the <function>_class_init ()</function> function. After creating the pad,
you have to set a <function>_chain ()</function> function pointer that will
receive and process the input data on the sinkpad.
You can optionally also set an <function>_event ()</function> function
pointer and a <function>_query ()</function> function pointer.
Alternatively, pads can also operate in looping mode, which means that they
can pull data themselves. More on this topic later. After that, you have
to register the pad with the element. This happens like this:
@ -30,26 +31,20 @@
static GstStateChangeReturn
gst_my_filter_change_state (GstElement * element, GstStateChange transition);
GST_BOILERPLATE (GstMyFilter, gst_my_filter, GstElement, GST_TYPE_ELEMENT);
G_DEFINE_TYPE (GstMyFilter, gst_my_filter, GST_TYPE_ELEMENT);
static void
gst_my_filter_base_init (gpointer klass)
gst_my_filter_class_init (gpointer klass)
{
GstElementClass *element_class = GST_ELEMENT_CLASS (klass);
static GstElementDetails my_filter_details = {
"An example plugin",
"Example/FirstExample",
"Shows the basic structure of a plugin",
"your name <your.name@your.isp>"
};
static GstStaticPadTemplate sink_factory =
static GstStaticPadTemplate sink_template =
GST_STATIC_PAD_TEMPLATE (
"sink",
GST_PAD_SINK,
GST_PAD_ALWAYS,
GST_STATIC_CAPS ("ANY")
);
static GstStaticPadTemplate src_factory =
static GstStaticPadTemplate src_template =
GST_STATIC_PAD_TEMPLATE (
"src",
GST_PAD_SRC,
@ -57,11 +52,16 @@ gst_my_filter_base_init (gpointer klass)
GST_STATIC_CAPS ("ANY")
);
gst_element_class_set_details (element_class, &my_filter_details);
gst_element_class_set_static_metadata (element_class,
"An example plugin",
"Example/FirstExample",
"Shows the basic structure of a plugin",
"your name <your.name@your.isp>");
gst_element_class_add_pad_template (element_class,
gst_static_pad_template_get (&src_factory));
gst_static_pad_template_get (&src_template));
gst_element_class_add_pad_template (element_class,
gst_static_pad_template_get (&sink_factory));
gst_static_pad_template_get (&sink_template));
}
static void
@ -70,43 +70,45 @@ gst_my_filter_class_init (GstMyFilterClass * klass)
GST_ELEMENT_CLASS (klass)->change_state = gst_my_filter_change_state;
}
--><!-- example-end init.func a -->
<!-- example-begin init.func b -->
static gboolean gst_my_filter_setcaps (GstPad *pad,
GstCaps *caps);
static GstFlowReturn gst_my_filter_chain (GstPad *pad,
GstBuffer *buf);
<!-- example-end init.func b -->
<!-- example-begin init.func c --><!--
static GstCaps * gst_my_filter_getcaps (GstPad *pad);
static gboolean gst_my_filter_event (GstPad *pad,
GstEvent *event);
static GstFlowReturn gst_my_filter_chain (GstPad *pad,
GstObject *parent,
GstBuffer *buf);
static gboolean gst_my_filter_sink_event (GstPad *pad,
GstObject *parent,
GstEvent *event);
static gboolean gst_my_filter_src_query (GstPad *pad,
GstObject *parent,
GstQuery *query);
static gboolean gst_my_filter_sink_query (GstPad *pad,
GstObject *parent,
GstQuery *query);
--><!-- example-end init.func c -->
<!-- example-begin init.func d -->
static void
gst_my_filter_init (GstMyFilter *filter, GstMyFilterClass *filter_klass)
gst_my_filter_init (GstMyFilter *filter)
{
GstElementClass *klass = GST_ELEMENT_CLASS (filter_klass);
/* pad through which data comes in to the element */
filter-&gt;sinkpad = gst_pad_new_from_template (
gst_element_class_get_pad_template (klass, "sink"), "sink");
gst_pad_set_setcaps_function (filter-&gt;sinkpad, gst_my_filter_setcaps);
gst_pad_set_chain_function (filter-&gt;sinkpad, gst_my_filter_chain);
filter-&gt;sinkpad = gst_pad_new_from_static_template (
&amp;sink_template, "sink");
/* pads are configured here with gst_pad_set_*_function () */
<!-- example-end init.func d -->
<!-- example-begin init.func e --><!--
gst_pad_set_getcaps_function (filter-&gt;sinkpad, gst_my_filter_getcaps);
gst_pad_set_event_function (filter-&gt;sinkpad, gst_my_filter_event);
gst_pad_set_chain_function (filter-&gt;sinkpad, gst_my_filter_chain);
gst_pad_set_event_function (filter-&gt;sinkpad, gst_my_filter_sink_event);
gst_pad_set_query_function (filter-&gt;sinkpad, gst_my_filter_sink_query);
--><!-- example-end init.func e -->
<!-- example-begin init.func f -->
gst_element_add_pad (GST_ELEMENT (filter), filter-&gt;sinkpad);
/* pad through which data goes out of the element */
filter-&gt;srcpad = gst_pad_new_from_template (
gst_element_class_get_pad_template (klass, "src"), "src");
filter-&gt;srcpad = gst_pad_new_from_static_template (
&amp;src_template, "src");
/* pads are configured here with gst_pad_set_*_function () */
<!-- example-end init.func f -->
<!-- example-begin init.func g --><!--
gst_pad_set_getcaps_function (filter-&gt;srcpad, gst_my_filter_getcaps);
gst_pad_set_query_function (filter-&gt;srcpad, gst_my_filter_src_query);
--><!-- example-end init.func g -->
<!-- example-begin init.func h -->
gst_element_add_pad (GST_ELEMENT (filter), filter-&gt;srcpad);
@ -116,105 +118,19 @@ gst_my_filter_init (GstMyFilter *filter, GstMyFilterClass *filter_klass)
}
<!-- example-end init.func h --></programlisting>
<sect1 id="section-pads-linkfn" xreflabel="The link function">
<title>The setcaps-function</title>
<para>
The <function>_setcaps ()</function>-function is called during caps
negotiation, which is discussed in great detail in <xref
linkend="chapter-negotiation"/>. This is the process where the linked
pads decide on the streamtype that will transfer between them. A full
list of type-definitions can be found in <xref
linkend="chapter-building-types"/>. A <function>_link ()</function>
receives a pointer to a <ulink type="http"
url="../../gstreamer/html/gstreamer-GstCaps.html"><classname>GstCaps</classname></ulink>
struct that defines the proposed streamtype, and can respond with
either <quote>yes</quote> (<symbol>TRUE</symbol>) or <quote>no</quote>
(<symbol>FALSE</symbol>). If the element responds positively towards
the streamtype, that type will be used on the pad. An example:
</para>
<programlisting><!-- example-begin caps.func a -->
static gboolean
gst_my_filter_setcaps (GstPad *pad,
GstCaps *caps)
{
GstStructure *structure = gst_caps_get_structure (caps, 0);
GstMyFilter *filter = GST_MY_FILTER (GST_OBJECT_PARENT (pad));
const gchar *media;
/* Since we're an audio filter, we want to handle raw audio
* and from that audio type, we need to get the samplerate and
* number of channels. */
media = gst_structure_get_name (structure);
if (strcmp (media, "audio/x-raw") != 0) {
GST_WARNING ("Wrong media type %s provided, we only support %s",
media, "audio/x-raw");
return FALSE;
}
/* we're a filter and don't touch the properties of the data.
* That means we can set the given caps unmodified on the next
* element, and use that negotiation return value as ours. */
if (!gst_pad_set_caps (filter-&gt;srcpad, caps))
return FALSE;
/* Capsnego succeeded, get the stream properties for internal
* usage and return success. */
gst_structure_get_int (structure, "rate", &amp;filter-&gt;samplerate);
gst_structure_get_int (structure, "channels", &amp;filter-&gt;channels);
g_print ("Caps negotiation succeeded with %d Hz @ %d channels\n",
filter-&gt;samplerate, filter-&gt;channels);
return TRUE;
}
<!-- example-end caps.func a -->
<!-- example-begin caps.func b --><!--
static GstCaps *
gst_my_filter_getcaps (GstPad * pad)
{
GstMyFilter *filter = GST_MY_FILTER (GST_OBJECT_PARENT (pad));
GstPad *otherpad = (pad == filter-&gt;srcpad) ? filter-&gt;sinkpad :
filter-&gt;srcpad;
GstCaps *othercaps = gst_pad_get_allowed_caps (otherpad);
return othercaps;
}
--><!-- example-end caps.func b --></programlisting>
<para>
In here, we check the media type of the provided caps. Normally, you don't
need to do that in your own plugin/element, because the core does that
for you. We simply use it to show how to retrieve the media type from a
provided set of caps. Types are stored in <ulink type="http"
url="../../gstreamer/html/gstreamer-GstStructure.html"><classname>GstStructure
</classname></ulink> internally. A <ulink
type="http" url="../../gstreamer/html/gstreamer-GstCaps.html"><classname>GstCaps
</classname></ulink> is nothing more than a small
wrapper for 0 or more structures/types. From the structure, you can also
retrieve properties, as is shown above with the function
<function>gst_structure_get_int ()</function>.
</para>
<para>
If your <function>_link ()</function> function does not need to perform
any specific operation (i.e. it will only forward caps), you can set it
to <function>gst_pad_proxy_link ()</function>. This is a link forwarding
function implementation provided by the core. It is useful for elements
such as <classname>identity</classname>.
</para>
</sect1>
<!-- example-begin pads.c --><!--
#include "init.func"
#include "caps.func"
static gboolean
gst_my_filter_event (GstPad * pad, GstEvent * event)
gst_my_filter_event (GstPad * pad, GstObject * parent, GstEvent * event)
{
return gst_pad_event_default (pad, event);
return gst_pad_event_default (pad, parent, event);
}
static GstFlowReturn
gst_my_filter_chain (GstPad * pad, GstBuffer * buf)
gst_my_filter_chain (GstPad * pad, GstObject * parent, GstBuffer * buf)
{
return gst_pad_push (GST_MY_FILTER (GST_OBJECT_PARENT (pad))->srcpad, buf);
return gst_pad_push (GST_MY_FILTER (parent)->srcpad, buf);
}
static GstStateChangeReturn

2
docs/pwg/pwg.xml
View file

@ -17,6 +17,7 @@
<!ENTITY BUILDING_DEBUG SYSTEM "building-debug.xml">
<!ENTITY BUILDING_PADS SYSTEM "building-pads.xml">
<!ENTITY BUILDING_CHAINFN SYSTEM "building-chainfn.xml">
<!ENTITY BUILDING_EVENTFN SYSTEM "building-eventfn.xml">
<!ENTITY BUILDING_STATE SYSTEM "building-state.xml">
<!ENTITY BUILDING_PROPS SYSTEM "building-props.xml">
<!ENTITY BUILDING_SIGNALS SYSTEM "building-signals.xml">
@ -116,6 +117,7 @@
&BUILDING_BOILER;
&BUILDING_PADS;
&BUILDING_CHAINFN;
&BUILDING_EVENTFN;
&BUILDING_STATE;
&BUILDING_PROPS;
&BUILDING_SIGNALS;