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<title>GstTagDemux: GStreamer Base Plugins 1.0 Library Reference Manual</title>
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<link rel="home" href="index.html" title="GStreamer Base Plugins 1.0 Library Reference Manual">
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<link rel="up" href="gstreamer-tag.html" title="Tag Support Library">
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<link rel="prev" href="gst-plugins-base-libs-GstTagXmpWriter.html" title="GstTagXmpWriter">
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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Description
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GstTagDemux
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GstTagDemux — Base class for demuxing tags that are in chunks
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directly at the beginning or at the end of a file
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Types and Values
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struct
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GstTagDemux
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struct
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GstTagDemuxClass
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enum
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GstTagDemuxResult
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Includes
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#include <gst/tag/gsttagdemux.h>
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Description
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Provides a base class for demuxing tags at the beginning or end of a
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stream and handles things like typefinding, querying, seeking, and
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different modes of operation (chain-based, pull_range-based, and providing
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downstream elements with random access if upstream supports that). The tag
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is stripped from the output, and all offsets are adjusted for the tag
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sizes, so that to the downstream element the stream will appear as if
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there was no tag at all. Also, once the tag has been parsed, GstTagDemux
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will try to determine the media type of the resulting stream and add a
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source pad with the appropriate caps in order to facilitate auto-plugging.
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Deriving from GstTagDemux
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Subclasses have to do four things:
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In their base init function, they must add a pad template for the sink
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pad to the element class, describing the media type they can parse in
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the caps of the pad template.
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In their class init function, they must override
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GST_TAG_DEMUX_CLASS(demux_klass)->identify_tag with their own identify
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function.
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In their class init function, they must override
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GST_TAG_DEMUX_CLASS(demux_klass)->parse_tag with their own parse
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function.
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In their class init function, they must also set
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GST_TAG_DEMUX_CLASS(demux_klass)->min_start_size and/or
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GST_TAG_DEMUX_CLASS(demux_klass)->min_end_size to the minimum size required
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for the identify function to decide whether the stream has a supported tag
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or not. A class parsing ID3v1 tags, for example, would set min_end_size to
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128 bytes.
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Functions
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Types and Values
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struct GstTagDemux
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struct GstTagDemux {
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GstElement element;
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};
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Opaque GstTagDemux structure.
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Members
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GstElement element;
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parent element
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struct GstTagDemuxClass
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struct GstTagDemuxClass {
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GstElementClass parent_class;
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/* minimum size required to identify a tag at the start and determine
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* its total size */
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guint min_start_size;
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/* minimum size required to identify a tag at the end and determine
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* its total size */
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guint min_end_size;
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/* vtable */
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/* identify tag and determine the size required to parse the tag */
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gboolean (*identify_tag) (GstTagDemux * demux,
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GstBuffer * buffer,
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gboolean start_tag,
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guint * tag_size);
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/* parse the tag once it is identified and its size is known */
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GstTagDemuxResult (*parse_tag) (GstTagDemux * demux,
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GstBuffer * buffer,
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gboolean start_tag,
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guint * tag_size,
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GstTagList ** tags);
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/* merge start and end tags (optional) */
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GstTagList * (*merge_tags) (GstTagDemux * demux,
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const GstTagList * start_tags,
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const GstTagList * end_tags);
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};
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The GstTagDemuxClass structure. See documentation at beginning of section
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for details about what subclasses need to override and do.
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Members
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guint min_start_size;
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minimum size required to identify a tag at the start and
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determine its total size. Set to 0 if not interested in start tags.
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Subclasses should set this in their class_init function.
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guint min_end_size;
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minimum size required to identify a tag at the end and
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determine its total size. Set to 0 if not interested in end tags.
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Subclasses should set this in their class_init function.
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identify_tag ()
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identify tag and determine the size required to parse the
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tag. Buffer may be larger than the specified minimum size.
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Subclassed MUST override this vfunc in their class_init function.
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parse_tag ()
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parse the tag. Buffer will be exactly of the size determined by
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the identify_tag vfunc before. The parse_tag vfunc may change the size
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stored in *tag_size and return GST_TAG_DEMUX_RESULT_AGAIN to request a
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larger or smaller buffer. It is also permitted to adjust the tag_size to a
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smaller value and then return GST_TAG_DEMUX_RESULT_OK in one go.
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Subclassed MUST override the parse_tag vfunc in their class_init function.
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merge_tags ()
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merge start and end tags. Subclasses may want to override this
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vfunc to allow prioritising of start or end tag according to user
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preference. Note that both start_tags and end_tags may be NULL. By default
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start tags are prefered over end tags.
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enum GstTagDemuxResult
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Result values from the parse_tag virtual function.
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Members
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GST_TAG_DEMUX_RESULT_BROKEN_TAG
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cannot parse tag, just skip it
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GST_TAG_DEMUX_RESULT_AGAIN
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call again with less or more data
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GST_TAG_DEMUX_RESULT_OK
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parsed tag successfully
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See Also
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GstApeDemux, GstID3Demux
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Generated by GTK-Doc V1.27
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