20xH264 Video Decode Render-less CPU Usage spike up to ~70% with flag sync=false

Submitted by Peng Chen @peng.chen

Link to original bug (#785092)

Description

1. Create a simple bash script with the 20x gstreamer execution command ( gst-launch-1.0 -v filesrc location=/videos/1920x1080_10mbps_30fps.mp4 ! qtdemux ! vaapidecode ! fpsdisplaysink video-sink=fakesink text-overlay=false sync=false)
2. Observed the CPU usage spike up to 70%
   3, Customer is expecting the CPU utilization result should not be so high if sync=false.Need to further to debug to find out the reason and root cause