/usr/share/doc/gstreamer0.10-doc/pwg/html/section-tagging-read.html

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>17.2. Reading Tags from Streams</A
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>&#13;      The basic object for tags is a <A
HREF="../../gstreamer/html/gstreamer-GstTagList.html"
TARGET="_top"
><CODE
CLASS="classname"
>GstTagList
      </CODE
></A
>. An element that is reading tags from a stream should
      create an empty taglist and fill this with individual tags. Empty tag
      lists can be created with <CODE
CLASS="function"
>gst_tag_list_new ()</CODE
>. Then,
      the element can fill the list using <CODE
CLASS="function"
>gst_tag_list_add ()
      </CODE
> or <CODE
CLASS="function"
>gst_tag_list_add_values ()</CODE
>.
      Note that elements often read metadata as strings, but the
      values in the taglist might not necessarily be strings - they need to be
      of the type the tag was registered as (the API documentation for each
      predefined tag should contain the type). Be sure to use functions like
      <CODE
CLASS="function"
>gst_value_transform ()</CODE
>
      to make sure that your data is of the right type. After data reading, the
      application can be notified of the new taglist by calling
      <CODE
CLASS="function"
>gst_element_found_tags ()</CODE
> or
      <CODE
CLASS="function"
>gst_element_found_tags_for_pad ()</CODE
> (if they only
      refer to a specific sub-stream). These functions will post a tag message
      on the pipeline's GstBus for the application to pick up, but also send
      tag events downstream, either over all source pad or the pad specified.
    </P
><P
>&#13;      We currently require the core to know the GType of tags before they are
      being used, so all tags must be registered first.  You can add new tags
      to the list of known tags using <CODE
CLASS="function"
>gst_tag_register ()</CODE
>.
      If you think the tag will be useful in more cases than just your own
      element, it might be a good idea to add it to <TT
CLASS="filename"
>gsttag.c</TT
>
      instead. That's up to you to decide. If you want to do it in your own
      element, it's easiest to register the tag in one of your class init
      functions, preferably <CODE
CLASS="function"
>_class_init ()</CODE
>.
    </P
><PRE
CLASS="programlisting"
>&#13;
static void
gst_my_filter_class_init (GstMyFilterClass *klass)
{
[..]
  gst_tag_register ("my_tag_name", GST_TAG_FLAG_META,
		    G_TYPE_STRING,
		    _("my own tag"),
		    _("a tag that is specific to my own element"),
		    NULL);
[..]
}

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gstreamer0.10-doc 0.10.36-1.5 / usr / share / doc / gstreamer0.10-doc / pwg / html / section-tagging-read.html
