How to seek pipeline with appsrc?

[Halley Zhao]

Hi expert:
I have special pipeline: appsrc-->h264parse-->h264dec-->videosink
and use a customized clock to control the pipeline.

when I want to do some seek operation, it doesn't work well. I tried to dig
into gstbasesink, but  still not a workable solution yet.

after play 3 seconds, I try to seek to 0 (file start)

approach 1: I also reset my clock time to restart from 0.
but, I found, the first buffer (pts=0) and other buffer before 3 second
timestamp are dropped. and after no video update for 3 seconds, video
playback continues with 3s+ frames.
I added some debug log to gstbasesink, and found that video frames before
3s are treated as 'too late' and are dropped.
I tried to compare it with seek of a normal pipeline
(filesrc-->qtdemux-->h264parse-->h264dec-->videosink), and found that the
base_time of gstbasesink is updated to the previous played time.
so I try to gst_element_set_base_time() for the elements of my appsrc
pipeline.
then the first video frame isn't dropped, but gst_base_sink_wait_clock()
from gst_base_sink_do_sync() is blocked for 3 seconds. then the first video
frame is rendered.

approach 2: I tried to create a new clock for the pipeline
after seek, I tried to use a new clock start from zero. it doesn't work
well either, because element base_time keeps big number,
gst_base_sink_wait_clock() is blocked for 3 seconds as well

to be honest, I don't know what's the correct way to seek a pipeline.
could anyone educate me on it?
maybe some segment event is required for seek, where is some reference code?
my test code see attachment.
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