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><H1
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><A
NAME="section-boiler-padtemplates"
>3.5. GstStaticPadTemplate</A
></H1
><P
> A GstStaticPadTemplate is a description of a pad that the element will
(or might) create and use. It contains:
</P
><P
></P
><UL
><LI
><P
>A short name for the pad.</P
></LI
><LI
><P
>Pad direction.</P
></LI
><LI
><P
> Existence property. This indicates whether the pad exists always (an
<SPAN
CLASS="QUOTE"
>"always"</SPAN
> pad), only in some cases (a
<SPAN
CLASS="QUOTE"
>"sometimes"</SPAN
> pad) or only if the application requested
such a pad (a <SPAN
CLASS="QUOTE"
>"request"</SPAN
> pad).
</P
></LI
><LI
><P
>Supported types by this element (capabilities).</P
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><P
> For example:
</P
><PRE
CLASS="programlisting"
> static GstStaticPadTemplate sink_factory =
GST_STATIC_PAD_TEMPLATE (
"sink",
GST_PAD_SINK,
GST_PAD_ALWAYS,
GST_STATIC_CAPS ("ANY")
);
</PRE
><P
> Those pad templates are registered during the
<CODE
CLASS="function"
>_base_init ()</CODE
> function. Pads are created from these
templates in the element's <CODE
CLASS="function"
>_init ()</CODE
> function using
<CODE
CLASS="function"
>gst_pad_new_from_template ()</CODE
>. The template can be
retrieved from the element class using
<CODE
CLASS="function"
>gst_element_class_get_pad_template ()</CODE
>. See below
for more details on this.
</P
><PRE
CLASS="programlisting"
> static void
gst_my_filter_base_init (GstMyFilterClass *klass)
{
static GstStaticPadTemplate sink_factory =
[..]
, src_factory =
[..]
GstElementClass *element_class = GST_ELEMENT_CLASS (klass);
gst_element_class_add_pad_template (element_class,
gst_static_pad_template_get (&src_factory));
gst_element_class_add_pad_template (element_class,
gst_static_pad_template_get (&sink_factory));
[..]
}
</PRE
><P
> The last argument in a template is its type
or list of supported types. In this example, we use 'ANY', which means
that this element will accept all input. In real-life situations, you
would set a mimetype and optionally a set of properties to make sure
that only supported input will come in. This representation should be
a string that starts with a mimetype, then a set of comma-separates
properties with their supported values. In case of an audio filter that
supports raw integer 16-bit audio, mono or stereo at any samplerate, the
correct template would look like this:
</P
><PRE
CLASS="programlisting"
> static GstStaticPadTemplate sink_factory =
GST_STATIC_PAD_TEMPLATE (
"sink",
GST_PAD_SINK,
GST_PAD_ALWAYS,
GST_STATIC_CAPS (
"audio/x-raw-int, "
"width = (int) 16, "
"depth = (int) 16, "
"endianness = (int) BYTE_ORDER, "
"channels = (int) { 1, 2 }, "
"rate = (int) [ 8000, 96000 ]"
)
);
</PRE
><P
> Values surrounded by {} are lists, values surrounded by [] are ranges.
Multiple sets of types are supported too, and should be separated by
a semicolon (<SPAN
CLASS="QUOTE"
>";"</SPAN
>). Later, in the chapter on pads, we will
see how to use types to know the exact format of a stream:
<A
HREF="chapter-building-pads.html"
>Chapter 4</A
>.
</P
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