GObject and calloc() etc are initializing memory to 0, so using 0 as the unknown variant makes it more likely that mistakingly zero-initialized memory does not end up with a wrong DSD format. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4966>
0xffffffff is mapped to 2**32 - 1 but GLib enums are signed ints so this value is out of range and causes problems with bindings. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4966>
Related to: https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/issues/972 Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3901>