The old API would only assert or return an invalid timecode, the new API
returns a boolean or NULL. We can't change the existing API
unfortunately but can at least deprecate it.
We need different export decorators for the different libs.
For now no actual change though, just rename before the release,
and add prelude headers to define the new decorator to GST_EXPORT.
Sometimes there is a human-oriented timecode that represents an
interval between two other timecodes. It corresponds to the human
perception of "add X hours" or "add X seconds" to a specific timecode,
taking drop-frame oddities into account. This interval-representing
timecode is now a GstVideoTimeCodeInterval. Also added function to add it to
a GstVideoTimeCode.
https://bugzilla.gnome.org/show_bug.cgi?id=776447
