A sink’s sync property controls whether buffers are pushed out at real-time pace (following their timestamps) or as fast as possible — it affects running time, not the PTS values themselves. See gstreamer for pipeline basics.
What Affects PTS vs. Running Time
If a sink (or an upstream element) has sync/set-timestamps enabled, samples are released close to real time; otherwise they flow as fast as the pipeline can process them. Either way, PTS values on the buffers are untouched by this setting — it only changes when a buffer carrying a given PTS is released, not the PTS itself.
Per-Element Notes
appsink
sync— affects running time only, doesn’t change PTS.
multiqueue
use-buffering— no effect on PTS.sync-by-running-time— no effect on PTS.use-interleave— no effect on PTS.
tsdemux
ignore-pcr— does affect PTS, by a constant offset.