The driver frame counters (processed, dropped, buffer level) are not
always correct apparently, and don't allow reliably assigning a frame
number to captured frames.
Instead of relying on them, count the number of frames directly here and
detect dropped frames based on the capture times of the frames: if more
than 1.75 frame durations are between two frames, then there must've
been a dropped frame.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7163>
3eec4703c6