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.
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.