[gstreamer-bugs] [Bug 599292] Synchronizing two RTP streams from different devices using RTCP is inaccurate.

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=599292
  GStreamer | gst-plugins-good | git

--- Comment #5 from Wim Taymans <wim.taymans at gmail.com> 2009-10-27 16:30:27 UTC ---
The NTP time that corresponds to an RTP time is taken from the buffer RTP
timestamp and the corresponding running_time on that buffer. We then also have
a mapping between running_time and NTP time. This last mapping is taken by
sampling the current system time when the pipeline goes to PLAYING.

When we need to calculate the NTP time for a buffer RTP time, we take the
running_time of that buffer and bring it back to NTP time. This assumes that
the running_time is aligned to the system time, which might not always be true.

Also another problem is that when you have multiple pipelines, they don't
always take the same system time as a base for NTP time.

Then the running_time can also drift from the system time if the pipeline clock
is not based on anything system time.

We would probably need to sample the system clock and the pipeline clock when
we need to generate an NTP time, then use the last running_time/RTP values of
the last buffer to scale the running_time back to system time.

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