How to seek pipeline with appsrc?

[Mathieu Duponchelle]

As far as I remember, appsrc is not really well suited for seeking, you
may want to consider writing a GstBaseSrc subclass.

On 6/14/19 1:09 PM, Halley Zhao wrote:
> 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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