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<a href="#gst-plugins-base-libs-gsttagdemux.description" class="shortcut">Description</a>
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<div class="refentry">
<a name="gst-plugins-base-libs-gsttagdemux"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
<td valign="top">
<h2><span class="refentrytitle"><a name="gst-plugins-base-libs-gsttagdemux.top_of_page"></a>gsttagdemux</span></h2>
<p>gsttagdemux — Base class for demuxing tags that are in chunks
directly at the beginning or at the end of a file</p>
</td>
<td valign="top" align="right"></td>
</tr></table></div>
<div class="refsynopsisdiv">
<a name="gst-plugins-base-libs-gsttagdemux.synopsis"></a><h2>Synopsis</h2>
<pre class="synopsis">
#include <gst/tag/gsttagdemux.h>
struct <a class="link" href="gst-plugins-base-libs-gsttagdemux.html#GstTagDemux" title="struct GstTagDemux">GstTagDemux</a>;
struct <a class="link" href="gst-plugins-base-libs-gsttagdemux.html#GstTagDemuxClass" title="struct GstTagDemuxClass">GstTagDemuxClass</a>;
enum <a class="link" href="gst-plugins-base-libs-gsttagdemux.html#GstTagDemuxResult" title="enum GstTagDemuxResult">GstTagDemuxResult</a>;
</pre>
</div>
<div class="refsect1">
<a name="gst-plugins-base-libs-gsttagdemux.description"></a><h2>Description</h2>
<p>
</p>
<div class="refsect2">
<a name="idp27038880"></a><h3>Deriving from GstTagDemux</h3>
<p>
Provides a base class for demuxing tags at the beginning or end of a
stream and handles things like typefinding, querying, seeking, and
different modes of operation (chain-based, pull_range-based, and providing
downstream elements with random access if upstream supports that). The tag
is stripped from the output, and all offsets are adjusted for the tag
sizes, so that to the downstream element the stream will appear as if
there was no tag at all. Also, once the tag has been parsed, GstTagDemux
will try to determine the media type of the resulting stream and add a
source pad with the appropriate caps in order to facilitate auto-plugging.
</p>
<p>
Subclasses have to do four things:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem"><p>
In their base init function, they must add a pad template for the sink
pad to the element class, describing the media type they can parse in
the caps of the pad template.
</p></li>
<li class="listitem"><p>
In their class init function, they must override
GST_TAG_DEMUX_CLASS(demux_klass)->identify_tag with their own identify
function.
</p></li>
<li class="listitem"><p>
In their class init function, they must override
GST_TAG_DEMUX_CLASS(demux_klass)->parse_tag with their own parse
function.
</p></li>
<li class="listitem"><p>
In their class init function, they must also set
GST_TAG_DEMUX_CLASS(demux_klass)->min_start_size and/or
GST_TAG_DEMUX_CLASS(demux_klass)->min_end_size to the minimum size required
for the identify function to decide whether the stream has a supported tag
or not. A class parsing ID3v1 tags, for example, would set min_end_size to
128 bytes.
</p></li>
</ul></div>
<p>
</p>
</div>
<p>
</p>
</div>
<div class="refsect1">
<a name="gst-plugins-base-libs-gsttagdemux.details"></a><h2>Details</h2>
<div class="refsect2">
<a name="GstTagDemux"></a><h3>struct GstTagDemux</h3>
<pre class="programlisting">struct GstTagDemux {
GstElement element;
};
</pre>
<p>
Opaque <a class="link" href="gst-plugins-base-libs-gsttagdemux.html#GstTagDemux" title="struct GstTagDemux"><span class="type">GstTagDemux</span></a> structure.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td><p><span class="term"><a href="/usr/share/gtk-doc/html/gstreamer-0.10/GstElement.html"><span class="type">GstElement</span></a> <em class="structfield"><code><a name="GstTagDemux.element"></a>element</code></em>;</span></p></td>
<td>parent element</td>
</tr></tbody>
</table></div>
<p class="since">Since 0.10.15</p>
</div>
<hr>
<div class="refsect2">
<a name="GstTagDemuxClass"></a><h3>struct GstTagDemuxClass</h3>
<pre class="programlisting">struct GstTagDemuxClass {
GstElementClass parent_class;
/* minimum size required to identify a tag at the start and determine
* its total size */
guint min_start_size;
/* minimum size required to identify a tag at the end and determine
* its total size */
guint min_end_size;
/* vtable */
/* identify tag and determine the size required to parse the tag */
gboolean (*identify_tag) (GstTagDemux * demux,
GstBuffer * buffer,
gboolean start_tag,
guint * tag_size);
/* parse the tag once it is identified and its size is known */
GstTagDemuxResult (*parse_tag) (GstTagDemux * demux,
GstBuffer * buffer,
gboolean start_tag,
guint * tag_size,
GstTagList ** tags);
/* merge start and end tags (optional) */
GstTagList * (*merge_tags) (GstTagDemux * demux,
const GstTagList * start_tags,
const GstTagList * end_tags);
};
</pre>
<p>
The <a class="link" href="gst-plugins-base-libs-gsttagdemux.html#GstTagDemuxClass" title="struct GstTagDemuxClass"><span class="type">GstTagDemuxClass</span></a> structure. See documentation at beginning of section
for details about what subclasses need to override and do.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><a href="/usr/share/gtk-doc/html/gstreamer-0.10/GstElement.html#GstElementClass"><span class="type">GstElementClass</span></a> <em class="structfield"><code><a name="GstTagDemuxClass.parent-class"></a>parent_class</code></em>;</span></p></td>
<td>the parent class.</td>
</tr>
<tr>
<td><p><span class="term"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#guint"><span class="type">guint</span></a> <em class="structfield"><code><a name="GstTagDemuxClass.min-start-size"></a>min_start_size</code></em>;</span></p></td>
<td>minimum size required to identify a tag at the start and
determine its total size. Set to 0 if not interested in start tags.
Subclasses should set this in their class_init function.</td>
</tr>
<tr>
<td><p><span class="term"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#guint"><span class="type">guint</span></a> <em class="structfield"><code><a name="GstTagDemuxClass.min-end-size"></a>min_end_size</code></em>;</span></p></td>
<td>minimum size required to identify a tag at the end and
determine its total size. Set to 0 if not interested in end tags.
Subclasses should set this in their class_init function.</td>
</tr>
<tr>
<td><p><span class="term"><em class="structfield"><code><a name="GstTagDemuxClass.identify-tag"></a>identify_tag</code></em> ()</span></p></td>
<td>identify tag and determine the size required to parse the
tag. Buffer may be larger than the specified minimum size.
Subclassed MUST override this vfunc in their class_init function.</td>
</tr>
<tr>
<td><p><span class="term"><em class="structfield"><code><a name="GstTagDemuxClass.parse-tag"></a>parse_tag</code></em> ()</span></p></td>
<td>parse the tag. Buffer will be exactly of the size determined by
the identify_tag vfunc before. The parse_tag vfunc may change the size
stored in *tag_size and return GST_TAG_DEMUX_RESULT_AGAIN to request a
larger or smaller buffer. It is also permitted to adjust the tag_size to a
smaller value and then return GST_TAG_DEMUX_RESULT_OK in one go.
Subclassed MUST override the parse_tag vfunc in their class_init function.</td>
</tr>
<tr>
<td><p><span class="term"><em class="structfield"><code><a name="GstTagDemuxClass.merge-tags"></a>merge_tags</code></em> ()</span></p></td>
<td>merge start and end tags. Subclasses may want to override this
vfunc to allow prioritising of start or end tag according to user
preference. Note that both start_tags and end_tags may be NULL. By default
start tags are prefered over end tags.</td>
</tr>
</tbody>
</table></div>
<p class="since">Since 0.10.15</p>
</div>
<hr>
<div class="refsect2">
<a name="GstTagDemuxResult"></a><h3>enum GstTagDemuxResult</h3>
<pre class="programlisting">typedef enum {
GST_TAG_DEMUX_RESULT_BROKEN_TAG,
GST_TAG_DEMUX_RESULT_AGAIN,
GST_TAG_DEMUX_RESULT_OK
} GstTagDemuxResult;
</pre>
<p>
Result values from the parse_tag virtual function.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><a name="GST-TAG-DEMUX-RESULT-BROKEN-TAG:CAPS"></a><span class="term"><code class="literal">GST_TAG_DEMUX_RESULT_BROKEN_TAG</code></span></p></td>
<td>cannot parse tag, just skip it
</td>
</tr>
<tr>
<td><p><a name="GST-TAG-DEMUX-RESULT-AGAIN:CAPS"></a><span class="term"><code class="literal">GST_TAG_DEMUX_RESULT_AGAIN</code></span></p></td>
<td>call again with less or more data
</td>
</tr>
<tr>
<td><p><a name="GST-TAG-DEMUX-RESULT-OK:CAPS"></a><span class="term"><code class="literal">GST_TAG_DEMUX_RESULT_OK</code></span></p></td>
<td>parsed tag successfully
</td>
</tr>
</tbody>
</table></div>
<p class="since">Since 0.10.15</p>
</div>
</div>
<div class="refsect1">
<a name="gst-plugins-base-libs-gsttagdemux.see-also"></a><h2>See Also</h2>
GstApeDemux, GstID3Demux
</div>
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