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.