how to sync audio and video in playbin3

[cfd new]

the problem is solved by setting sync of sink to true. But its default value is true. Weird.
   On Monday, August 21, 2023, 06:35:41 p.m. EDT, cfd new via gstreamer-devel <gstreamer-devel at lists.freedesktop.org> wrote:  
 
 I use playbin3 to display rtsp streaming and noticed audio is slightly behind video in the display. How to sync audio and video? Thanks for your kind help.
   Joe
  
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