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115 lines
2.9 KiB
Plaintext
115 lines
2.9 KiB
Plaintext
<!-- ##### SECTION Title ##### -->
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Writing typefind functions
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<!-- ##### SECTION Short_Description ##### -->
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Using the type finding subsystem from plugins
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<!-- ##### SECTION Long_Description ##### -->
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<para>
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The typefinding subsystem in GStreamer is used to find the matching #GstCaps
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for an unidentified stream. This works similar to the unix <emphasis>file
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</emphasis> command.
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</para>
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<para>
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There are a number of elements which output unidentified data streams, such as
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a file source. Some other elements such as an autoplugger require a proper
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identification of the data, so they can create the right pipeline. To find the
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right type, they use typefinding elements, the most notable being the typefind
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element. These elements take a list of all registered typefind functions and
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try them on the data to see if any of these functions can identify the data.
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</para>
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<para>
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The functions in this section provide the simple framework for writing these
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typefind functions. The job of a typefind function is to identify the type of
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the data good enough so that plugins using this type can understand them while
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make sure no other type is misidentified.
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<example>
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<title>a typefind function for Ogg data</title>
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<programlisting>
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static void
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ogg_type_find (GstTypeFind *tf, gpointer unused)
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{
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guint8 *data = gst_type_find_peek (tf, 0, 4);
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if (data && memcmp (data, "OggS", 4) == 0) {
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gst_type_find_suggest (tf, GST_TYPE_FIND_MAXIMUM,
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gst_caps_new ("ogg_type_find", "application/ogg", NULL));
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}
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};
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</programlisting>
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</example>
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</para>
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<!-- ##### SECTION See_Also ##### -->
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<para>
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<link linkend="GstTypeFindFactory">GstTypeFactory - querying registered typefind
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functions</link>
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</para>
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<!-- ##### STRUCT GstTypeFind ##### -->
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<para>
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This structure is filled by the caller of the typefind function. Typefind
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functions must treat this as an opaque structure.
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</para>
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@peek: function called to get data. See gst_type_find_peek()
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@suggest: function called to suggest a caps. See gst_type_find_suggest()
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@data: caller defined data, that is passed when calling the functions
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@get_length: function called to query the length of the stream. See
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gst_type_find_get_length(). Providing this function is optional.
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<!-- ##### USER_FUNCTION GstTypeFindFunction ##### -->
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<para>
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This is the prototype for a typefind function.
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</para>
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@find: The #GstTypeFind data
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@data: the user defined data that was provided on
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gst_type_find_factory_register()
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<!-- ##### FUNCTION gst_type_find_peek ##### -->
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<para>
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</para>
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@find:
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@offset:
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@size:
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@Returns:
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<!-- ##### FUNCTION gst_type_find_suggest ##### -->
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<para>
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</para>
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@find:
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@probability:
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@caps:
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<!-- ##### FUNCTION gst_type_find_get_length ##### -->
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<para>
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</para>
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@find:
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@Returns:
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<!-- ##### FUNCTION gst_type_find_factory_register ##### -->
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<para>
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</para>
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@plugin:
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@name:
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@rank:
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@func:
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@extensions:
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@possible_caps:
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@data:
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