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