what would happen if the time returned by gst_clock_get_time decrease

[chensheng duan]

hi there:
         we came cross a problem that we need to roll back the time returned
by the gst_clock_get_time under some situation. the background list as
below:
         we run gstreamer on our arm board, and our audio hardware decode
and render run as 1x normal speed all the time while video hardware decode
and render can run as much faster as it can(maybe several times than 1x
speed), so the problem is , if sometimes video data delay when recieved by
decode , just drop the delayed buffer in render, and video decode can push
the following buffer asap, but if audio data delay when recieved by audio
decode , no matter drop or not in render , the pts cannot catch up with the
correct render time since if audio data late 2s when in decode , and audio
decode run as 1x speed, then it will late permanently 2s.
         so we decide to use audiosink to provide clock, the clock still is
systime clock, but if we found audio late 2s for ex, we will return
(current_sys_clock_time -2s) to make video delay for 2 seconds to make video
wait for audio.  it will draw back pipeline clock ,  i dont know if it will
cause some problems. and if you guys have some idea , plz give me some
advices, thx in advance!
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