The 'new-pref' property sets the preference to use the new (next)
instead of the old (previous) buffer. The default is set to 0.5 to get
a similar behaviour as before the change.
Value 0.0 makes sure that only frames are shown where it's known that
the frame content is visible at that time, always show the old frame
until the new frame timestamp is reached.
Then, if the next buffer replaces the previous buffer the new buffer
is pushed as often as possible until PTS is reached. Before the new
buffer was only pushed once the new next buffer arrived.
Use GstClockTimeDiff because it's known that the current buffer time
is inside the time interval of previous buffer and next buffer the
calculation can be done with building absolute values. Special macros
are not needed here.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8579>
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