GstTagDemux

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.

Deriving from GstTagDemux

Subclasses have to do four things:

  • 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.
  • In their class init function, they must override GST_TAG_DEMUX_CLASS(demux_klass)->identify_tag with their own identify function.
  • In their class init function, they must override GST_TAG_DEMUX_CLASS(demux_klass)->parse_tag with their own parse function.
  • 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.

GstTagDemux 

GObject
    ╰──GInitiallyUnowned
        ╰──GstObject
            ╰──GstElement
                ╰──GstTagDemux

Opaque GstTagDemux structure.

Members

element (GstElement) –

parent element

Class structure

GstTagDemuxClass

The GstTagDemuxClass structure. See documentation at beginning of section for details about what subclasses need to override and do.

Fields
parent_class (GstElementClass) –

the parent class.

min_start_size (guint) –

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.

min_end_size (guint) –

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.

GstTag.TagDemuxClass

The GstTag.TagDemuxClass structure. See documentation at beginning of section for details about what subclasses need to override and do.

Attributes
parent_class (Gst.ElementClass) –

the parent class.

min_start_size (Number) –

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.

min_end_size (Number) –

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.

GstTag.TagDemuxClass

The GstTag.TagDemuxClass structure. See documentation at beginning of section for details about what subclasses need to override and do.

Attributes
parent_class (Gst.ElementClass) –

the parent class.

min_start_size (int) –

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.

min_end_size (int) –

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.

GstTag.TagDemux 

GObject.Object
    ╰──GObject.InitiallyUnowned
        ╰──Gst.Object
            ╰──Gst.Element
                ╰──GstTag.TagDemux

Opaque GstTag.TagDemux structure.

Members

element (Gst.Element) –

parent element

GstTag.TagDemux 

GObject.Object
    ╰──GObject.InitiallyUnowned
        ╰──Gst.Object
            ╰──Gst.Element
                ╰──GstTag.TagDemux

Opaque GstTag.TagDemux structure.

Members

element (Gst.Element) –

parent element

Virtual Methods

identify_tag 

gboolean
identify_tag (GstTagDemux * demux,
              GstBuffer * buffer,
              gboolean start_tag,
              guint * tag_size)

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.

Parameters:

demux –
No description available
buffer –
No description available
start_tag –
No description available
tag_size –
No description available
Returns –
No description available

vfunc_identify_tag 

function vfunc_identify_tag(demux: GstTag.TagDemux, buffer: Gst.Buffer, start_tag: Number, tag_size: Number): {
    // javascript implementation of the 'identify_tag' virtual method
}

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.

Parameters:

demux (GstTag.TagDemux) –
No description available
buffer (Gst.Buffer) –
No description available
start_tag (Number) –
No description available
tag_size (Number) –
No description available
Returns (Number) –
No description available

do_identify_tag 

def do_identify_tag (demux, buffer, start_tag, tag_size):
    #python implementation of the 'identify_tag' virtual method

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.

Parameters:

demux (GstTag.TagDemux) –
No description available
buffer (Gst.Buffer) –
No description available
start_tag (bool) –
No description available
tag_size (int) –
No description available
Returns (bool) –
No description available

merge_tags 

GstTagList *
merge_tags (GstTagDemux * demux,
            const GstTagList * start_tags,
            const GstTagList * end_tags)

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 preferred over end tags.

Parameters:

demux –
No description available
start_tags –
No description available
end_tags –
No description available
Returns –
No description available

vfunc_merge_tags 

function vfunc_merge_tags(demux: GstTag.TagDemux, start_tags: Gst.TagList, end_tags: Gst.TagList): {
    // javascript implementation of the 'merge_tags' virtual method
}

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 preferred over end tags.

Parameters:

demux (GstTag.TagDemux) –
No description available
start_tags (Gst.TagList) –
No description available
end_tags (Gst.TagList) –
No description available
Returns (Gst.TagList) –
No description available

do_merge_tags 

def do_merge_tags (demux, start_tags, end_tags):
    #python implementation of the 'merge_tags' virtual method

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 preferred over end tags.

Parameters:

demux (GstTag.TagDemux) –
No description available
start_tags (Gst.TagList) –
No description available
end_tags (Gst.TagList) –
No description available
Returns (Gst.TagList) –
No description available

parse_tag 

GstTagDemuxResult
parse_tag (GstTagDemux * demux,
           GstBuffer * buffer,
           gboolean start_tag,
           guint * tag_size,
           GstTagList ** tags)

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.

Parameters:

demux –
No description available
buffer –
No description available
start_tag –
No description available
tag_size –
No description available
tags –
No description available
Returns –
No description available

vfunc_parse_tag 

function vfunc_parse_tag(demux: GstTag.TagDemux, buffer: Gst.Buffer, start_tag: Number, tag_size: Number, tags: Gst.TagList): {
    // javascript implementation of the 'parse_tag' virtual method
}

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.

Parameters:

demux (GstTag.TagDemux) –
No description available
buffer (Gst.Buffer) –
No description available
start_tag (Number) –
No description available
tag_size (Number) –
No description available
tags (Gst.TagList) –
No description available
Returns (GstTag.TagDemuxResult) –
No description available

do_parse_tag 

def do_parse_tag (demux, buffer, start_tag, tag_size, tags):
    #python implementation of the 'parse_tag' virtual method

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.

Parameters:

demux (GstTag.TagDemux) –
No description available
buffer (Gst.Buffer) –
No description available
start_tag (bool) –
No description available
tag_size (int) –
No description available
tags (Gst.TagList) –
No description available
Returns (GstTag.TagDemuxResult) –
No description available

Enumerations

GstTagDemuxResult

Result values from the parse_tag virtual function.

Members
GST_TAG_DEMUX_RESULT_BROKEN_TAG (0) –

cannot parse tag, just skip it

GST_TAG_DEMUX_RESULT_AGAIN (1) –

call again with less or more data

GST_TAG_DEMUX_RESULT_OK (2) –

parsed tag successfully

GstTag.TagDemuxResult

Result values from the parse_tag virtual function.

Members
GstTag.TagDemuxResult.BROKEN_TAG (0) –

cannot parse tag, just skip it

GstTag.TagDemuxResult.AGAIN (1) –

call again with less or more data

GstTag.TagDemuxResult.OK (2) –

parsed tag successfully

GstTag.TagDemuxResult

Result values from the parse_tag virtual function.

Members
GstTag.TagDemuxResult.BROKEN_TAG (0) –

cannot parse tag, just skip it

GstTag.TagDemuxResult.AGAIN (1) –

call again with less or more data

GstTag.TagDemuxResult.OK (2) –

parsed tag successfully

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