rtpbin: updating ts_offset often cause audio glitches when using ntp-sync=true

Submitted by Danny

Link to original bug (#794762)

Description

Following the procedure outlined in the pdf below we have encountered audio glitches in our audio receivers. Have tracked it down to that constantly updating the ts_offset in the rtpbin results in glitches when streaming audio using ntp-sync=true. Seems to be related to jittery behaviour in the local/remote clock causing the ts_offset to be updated often with very small changes (<100 microseconds) which in turn causes the alsasink to jump around in its audio buffer.

https://gstreamer.freedesktop.org/data/events/gstreamer-conference/2015/Sebastian%20Dr%C3%B6ge%20-%20Synchronised%20multi-room%20media%20playback%20and%20distributed%20live%20media%20processing%20and%20mixing%20with%20GStreamer.pdf

Version: 1.14.0