gstreamer/docs/manual/links.xml

107 lines
3 KiB
XML
Raw Normal View History

<chapter id="cha-links">
<title>Linking elements</title>
<para>
You can link the different pads of elements together so that the elements
form a chain.
</para>
<figure float="1" id="sec-link">
<title>Visualisation of three linked elements</title>
<mediaobject>
<imageobject>
<imagedata fileref="images/linked-elements.&image;" format="&IMAGE;" />
</imageobject>
</mediaobject>
</figure>
<para>
By linking these three elements, we have created a very simple
chain. The effect of this will be that the output of the source element
(element1) will be used as input for the filter element (element2). The
filter element will do something with the data and send the result to
the final sink element (element3).
</para>
<para>
Imagine the above graph as a simple MPEG audio decoder. The source
element is a disk source, the filter element is the MPEG decoder and
the sink element is your audiocard. We will use this simple graph to
construct an MPEG player later in this manual.
</para>
<sect1 id="sec-link-basic">
<title>Making simple links</title>
<para>
You can link two pads with:
</para>
<programlisting>
GstPad *srcpad, *sinkpad;
srcpad = gst_element_get_pad (element1, "src");
sinpad = gst_element_get_pad (element2, "sink");
// link them
gst_pad_link (srcpad, sinkpad);
....
// and unlink them
gst_pad_unlink (srcpad, sinkpad);
</programlisting>
<para>
A convenient shortcut for the above code is done with the gst_element_link_pads ()
function:
</para>
<programlisting>
// link them
gst_element_link_pads (element1, "src", element2, "sink");
....
// and unlink them
gst_element_unlink_pads (element1, "src", element2, "sink");
</programlisting>
<para>
An even more convenient shortcut for single-source, single-sink elements is the
gst_element_link () function:
</para>
<programlisting>
// link them
gst_element_link (element1, element2);
....
// and unlink them
gst_element_unlink (element1, element2);
</programlisting>
<para>
If you have more than one element to link, the gst_element_link_many () function takes
a NULL-terminated list of elements:
</para>
<programlisting>
// link them
gst_element_link_many (element1, element2, element3, element4, NULL);
....
// and unlink them
gst_element_unlink_many (element1, element2, element3, element4, NULL);
</programlisting>
<para>
You can query if a pad is linked with GST_PAD_IS_LINKED (pad).
</para>
<para>
To query for the <classname>GstPad</classname> a pad is linked to, use
gst_pad_get_peer (pad).
</para>
</sect1>
<sect1 id="sec-link-filtered">
<title>Making filtered links</title>
<para>
You can also force a specific media type on the link by using gst_pad_link_filtered ()
and gst_element_link_filtered () with capabilities.
See <xref linkend="sec-caps"/> for
an explanation of capabilities.
</para>
</sect1>
</chapter>